diff --git a/src/App.tsx b/src/App.tsx
index e503545..ed466b2 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -19,9 +19,11 @@ import type { RenderingEvent } from './core/audio-interface/KGOfflineRenderer';
 import { KGCore } from './core/KGCore';
 import { ConfigManager } from './core/config/ConfigManager';
 import { validateFunctionalChordsJSON } from './util/scaleUtil';
+import { buildChordGuideDataFromDefaultsAndConfig } from './util/chordGuideConfigUtil';
 import { showAlert } from './util/dialogUtil';
 import { KGProjectStorage } from './core/io/KGProjectStorage';
 import { RESERVED_PROJECT_NAME } from './util/projectNameUtil';
+import type { ChordGuideCustomConfig } from './core/ChordGuideTypes';
 
 function App() {
   // Enable global keyboard handler for copy/paste and undo/redo
@@ -60,7 +62,8 @@ function App() {
       loadProject(null);
 
       // Initialize ConfigManager first to load config.json and user settings
-      await ConfigManager.instance().initialize();
+      const configManager = ConfigManager.instance();
+      await configManager.initialize();
 
       // Check for kgone-server.json (managed deployment override)
       try {
@@ -99,11 +102,11 @@ function App() {
         // Store original functional chords data
         KGCore.ORIGINAL_FUNCTIONAL_CHORDS_DATA = functionalChordsData;
         console.log(`Loaded original functional chords for ${Object.keys(functionalChordsData).length} modes`);
-        KGCore.CHORD_GUIDE_DATA = chordGuideData;
+        const customChordGuideItems = configManager.get('chord_guide.custom_items') as ChordGuideCustomConfig | null | undefined;
+        KGCore.CHORD_GUIDE_DATA = buildChordGuideDataFromDefaultsAndConfig(chordGuideData, customChordGuideItems);
         console.log(`Loaded chord guide data for ${Object.keys(chordGuideData).length} modes`);
 
         // Check if custom chord definition exists and is valid
-        const configManager = ConfigManager.instance();
         const customDefinition = configManager.get('chord_guide.chord_definition') as string;
 
         if (customDefinition && customDefinition.trim()) {
diff --git a/src/components/StatusBar.test.tsx b/src/components/StatusBar.test.tsx
new file mode 100644
index 0000000..e153e03
--- /dev/null
+++ b/src/components/StatusBar.test.tsx
@@ -0,0 +1,83 @@
+import React from 'react';
+import { act, render, screen } from '@testing-library/react';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import StatusBar from './StatusBar';
+import { KGPianoRollState } from '../core/state/KGPianoRollState';
+import { KGCore } from '../core/KGCore';
+import type { ChordGuideData } from '../core/ChordGuideTypes';
+import { resolveChordGuideItems } from '../util/chordGuideDataUtil';
+import type { ResolvedChordGuideItem } from '../core/ChordGuideTypes';
+import chordGuideDataJson from '../../public/resources/modes/chord_guide.json';
+
+const chordGuideData = chordGuideDataJson as ChordGuideData;
+
+const storeState = {
+  currentStatus: 'Ready',
+};
+
+type StoreState = typeof storeState;
+type StoreSelector = (state: StoreState) => unknown;
+
+vi.mock('../stores/projectStore', () => ({
+  useProjectStore: Object.assign(
+    (selector?: StoreSelector) => (selector ? selector(storeState) : storeState),
+    { getState: () => storeState }
+  ),
+}));
+
+describe('StatusBar', () => {
+  beforeEach(() => {
+    vi.stubGlobal('__APP_VERSION__', 'test-version');
+    storeState.currentStatus = 'Ready';
+    KGCore.CHORD_GUIDE_DATA = structuredClone(chordGuideData);
+    KGPianoRollState.instance().setCurrentHoveredChordGuideCandidate(null);
+  });
+
+  it('shows the normal status when no chord-guide candidate is hovered', () => {
+    render(<StatusBar />);
+
+    expect(screen.getByText('Ready')).toBeTruthy();
+  });
+
+  it('shows hovered chord-guide candidate text and restores the prior status when cleared', () => {
+    render(<StatusBar />);
+
+    const hoveredCandidate: ResolvedChordGuideItem = {
+      name: 'Dm7',
+      roman: 'ii7',
+      notes: ['D', 'F', 'A', 'C'],
+      source: 'Diatonic',
+      note: 'Core ii-V-I predominant sonority.',
+      resolvedNotes: ['D', 'F', 'A', 'C'],
+      pitchClasses: [2, 5, 9, 12],
+    };
+
+    act(() => {
+      KGPianoRollState.instance().setCurrentHoveredChordGuideCandidate(hoveredCandidate);
+    });
+
+    expect(
+      screen.getByText('Chord Guide Candidate: Dm7 — D F A C — Core ii-V-I predominant sonority.')
+    ).toBeTruthy();
+
+    act(() => {
+      KGPianoRollState.instance().setCurrentHoveredChordGuideCandidate(null);
+    });
+
+    expect(screen.getByText('Ready')).toBeTruthy();
+  });
+
+  it('uses resolved notes from the current key signature in the status text', () => {
+    const transposedCandidate = resolveChordGuideItems('D major', 'ionian', 'T')[0];
+
+    render(<StatusBar />);
+
+    act(() => {
+      KGPianoRollState.instance().setCurrentHoveredChordGuideCandidate(transposedCandidate);
+    });
+
+    expect(
+      screen.getByText('Chord Guide Candidate: C — D F# A — Most stable tonic triad.')
+    ).toBeTruthy();
+  });
+});
diff --git a/src/components/StatusBar.tsx b/src/components/StatusBar.tsx
index 17f23a5..9018eb4 100644
--- a/src/components/StatusBar.tsx
+++ b/src/components/StatusBar.tsx
@@ -1,14 +1,28 @@
-import React from 'react';
+import React, { useSyncExternalStore } from 'react';
 import './StatusBar.css';
 import { useProjectStore } from '../stores/projectStore';
+import { KGPianoRollState } from '../core/state/KGPianoRollState';
+import type { ResolvedChordGuideItem } from '../core/ChordGuideTypes';
+
+function formatChordGuideCandidateStatus(candidate: ResolvedChordGuideItem): string {
+  return `Chord Guide Candidate: ${candidate.name} — ${candidate.resolvedNotes.join(' ')} — ${candidate.note}`;
+}
 
 const StatusBar: React.FC = () => {
   const { currentStatus } = useProjectStore();
+  const hoveredChordGuideCandidate = useSyncExternalStore(
+    (listener) => KGPianoRollState.instance().subscribe(listener),
+    () => KGPianoRollState.instance().getCurrentHoveredChordGuideCandidate(),
+    () => null,
+  );
+  const statusText = hoveredChordGuideCandidate
+    ? formatChordGuideCandidateStatus(hoveredChordGuideCandidate)
+    : currentStatus;
 
   return (
     <div className="status-bar">
-      <div className="status-left">
-        {currentStatus}
+      <div className="status-left" title={statusText}>
+        {statusText}
       </div>
       <div className="status-right">
         <span>K.G.Studio (v{__APP_VERSION__})</span>
@@ -17,4 +31,5 @@ const StatusBar: React.FC = () => {
   );
 };
 
-export default StatusBar; 
\ No newline at end of file
+export default StatusBar; 
+export { formatChordGuideCandidateStatus };
diff --git a/src/components/piano-roll/PianoGrid.tsx b/src/components/piano-roll/PianoGrid.tsx
index bcb137f..978a623 100644
--- a/src/components/piano-roll/PianoGrid.tsx
+++ b/src/components/piano-roll/PianoGrid.tsx
@@ -11,7 +11,7 @@ import AudioWaveformCanvas from './AudioWaveformCanvas';
 import type { KGAudioRegion } from '../../core/region/KGAudioRegion';
 import type { SpectrogramHeightResolution } from '../../util/spectrogramUtil';
 import { getNextChordCandidateIndex } from './chordGuideUtil';
-import { getMatchingChordGuideChordsForPitch } from '../../util/chordGuideDataUtil';
+import { getMatchingChordGuideCandidatesForPitch } from '../../util/chordGuideDataUtil';
 
 interface PianoGridProps {
   gridRef: MutableRefObject<HTMLDivElement | null>;
@@ -160,24 +160,28 @@ const PianoGrid: React.FC<PianoGridProps> = ({
   };
 
   // Get all matching chords for the current hover position
-  const matchingChords = useMemo(() => {
+  const matchingCandidates = useMemo(() => {
     if (!cursorPosition) return [];
 
     // If chord guide is disabled, return empty array
     if (chordGuide === 'N') return [];
 
-    // Use the utility function to get matching chords
+    // Use the utility function to get matching chords in the same order used by candidate cycling.
     const functionType = chordGuide as 'T' | 'S' | 'D';
-    return getMatchingChordGuideChordsForPitch(cursorPosition.pitch, chordGuideKeySignature, chordGuideMode, functionType);
+    return getMatchingChordGuideCandidatesForPitch(cursorPosition.pitch, chordGuideKeySignature, chordGuideMode, functionType);
   }, [cursorPosition, chordGuide, chordGuideKeySignature, chordGuideMode]);
 
+  const matchingChords = useMemo(() => (
+    matchingCandidates.map((candidate) => candidate.displayPitchClasses)
+  ), [matchingCandidates]);
+
   // Calculate chord highlights based on selected chord index
   const chordHighlights = useMemo(() => {
-    if (matchingChords.length === 0) return [];
+    if (matchingCandidates.length === 0) return [];
 
     // Use the selected chord index (wrap around if needed)
-    const chordIndex = selectedChordIndex % matchingChords.length;
-    const matchedChordPitches = matchingChords[chordIndex];
+    const chordIndex = selectedChordIndex % matchingCandidates.length;
+    const matchedChordPitches = matchingCandidates[chordIndex].displayPitchClasses;
 
     // Convert pitch classes to actual pitches in the same octave as cursor
     const highlights: Array<{ pitch: number; beat: number }> = [];
@@ -195,15 +199,22 @@ const PianoGrid: React.FC<PianoGridProps> = ({
     }
 
     return highlights;
-  }, [cursorPosition, matchingChords, selectedChordIndex]);
+  }, [cursorPosition, matchingCandidates, selectedChordIndex]);
 
   const cursorPitch = cursorPosition?.pitch ?? null;
+  const selectedHoverCandidate = useMemo(() => {
+    if (matchingCandidates.length === 0) {
+      return null;
+    }
+    return matchingCandidates[selectedChordIndex % matchingCandidates.length].item;
+  }, [matchingCandidates, selectedChordIndex]);
 
   useEffect(() => {
     const pianoRollState = KGPianoRollState.instance();
     pianoRollState.setCurrentMatchingChords(matchingChords);
     pianoRollState.setCurrentChordCursorPitch(cursorPitch);
-  }, [matchingChords, cursorPitch]);
+    pianoRollState.setCurrentHoveredChordGuideCandidate(selectedHoverCandidate);
+  }, [matchingChords, cursorPitch, selectedHoverCandidate]);
 
   useEffect(() => {
     KGPianoRollState.instance().setCurrentSelectedChordIndex(selectedChordIndex);
@@ -219,8 +230,8 @@ const PianoGrid: React.FC<PianoGridProps> = ({
   // Expose switchChord function via window for hotkey handler
   useEffect(() => {
     const switchChord = (direction: 1 | -1 = 1) => {
-      if (matchingChords.length > 1) {
-        setSelectedChordIndex(prev => getNextChordCandidateIndex(prev, matchingChords.length, direction));
+      if (matchingCandidates.length > 1) {
+        setSelectedChordIndex(prev => getNextChordCandidateIndex(prev, matchingCandidates.length, direction));
       }
     };
 
@@ -232,7 +243,7 @@ const PianoGrid: React.FC<PianoGridProps> = ({
       // eslint-disable-next-line @typescript-eslint/no-explicit-any
       delete (window as any).__pianoGridSwitchChord;
     };
-  }, [matchingChords.length]);
+  }, [matchingCandidates.length]);
 
   return (
     <div className="piano-grid-container">
diff --git a/src/components/piano-roll/PianoGridCandidateStatus.test.tsx b/src/components/piano-roll/PianoGridCandidateStatus.test.tsx
new file mode 100644
index 0000000..ea9747b
--- /dev/null
+++ b/src/components/piano-roll/PianoGridCandidateStatus.test.tsx
@@ -0,0 +1,96 @@
+import React from 'react';
+import { fireEvent, render, waitFor } from '@testing-library/react';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { KGCore } from '../../core/KGCore';
+import type { ChordGuideData } from '../../core/ChordGuideTypes';
+import { KGPianoRollState } from '../../core/state/KGPianoRollState';
+import { getMatchingChordGuideCandidatesForPitch } from '../../util/chordGuideDataUtil';
+import chordGuideDataJson from '../../../public/resources/modes/chord_guide.json';
+
+const chordGuideData = chordGuideDataJson as ChordGuideData;
+
+vi.mock('../common', () => ({
+  Playhead: () => null,
+}));
+
+import PianoGrid from './PianoGrid';
+
+describe('PianoGrid chord-guide hover candidate state', () => {
+  beforeEach(() => {
+    document.documentElement.style.setProperty('--region-grid-beat-width', '40');
+    document.documentElement.style.setProperty('--region-piano-key-height', '20');
+    KGCore.CHORD_GUIDE_DATA = structuredClone(chordGuideData);
+    KGCore.FUNCTIONAL_CHORDS_DATA = {
+      ionian: { steps: [2, 2, 1, 2, 2, 2, 1] },
+      aeolian: { steps: [2, 1, 2, 2, 1, 2, 2] },
+    } as unknown as typeof KGCore.FUNCTIONAL_CHORDS_DATA;
+    KGPianoRollState.instance().setCurrentHoveredChordGuideCandidate(null);
+    KGPianoRollState.instance().setCurrentMatchingChords([]);
+    KGPianoRollState.instance().setCurrentSelectedChordIndex(0);
+    KGPianoRollState.instance().setCurrentChordCursorPitch(null);
+  });
+
+  it('tracks the hovered candidate, updates on candidate cycling, and clears on mouse leave', async () => {
+    const gridRef = { current: null as HTMLDivElement | null };
+    const { container } = render(
+      <PianoGrid
+        gridRef={gridRef}
+        onDoubleClick={() => {}}
+        onClick={() => {}}
+        onMouseDown={() => {}}
+        isBoxSelecting={false}
+        selectionBox={{ startX: 0, startY: 0, endX: 0, endY: 0 }}
+        selectedMode="ionian"
+        keySignature="C major"
+        chordGuide="T"
+        chordGuideKeySignature="C major"
+        chordGuideMode="ionian"
+      >
+        {null}
+      </PianoGrid>
+    );
+
+    const pianoGrid = container.querySelector('.piano-grid') as HTMLDivElement;
+    pianoGrid.getBoundingClientRect = () => ({
+      left: 0,
+      top: 0,
+      width: 800,
+      height: 1200,
+      right: 800,
+      bottom: 1200,
+      x: 0,
+      y: 0,
+      toJSON: () => ({}),
+    });
+
+    fireEvent.mouseMove(pianoGrid, { clientX: 10, clientY: 941 });
+
+    const expectedCandidates = getMatchingChordGuideCandidatesForPitch(60, 'C major', 'ionian', 'T');
+    expect(expectedCandidates.length).toBeGreaterThan(1);
+
+    await waitFor(() => {
+      expect(KGPianoRollState.instance().getCurrentHoveredChordGuideCandidate()).toMatchObject({
+        name: expectedCandidates[0].item.name,
+        resolvedNotes: expectedCandidates[0].item.resolvedNotes,
+        note: expectedCandidates[0].item.note,
+      });
+    });
+
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    (window as any).__pianoGridSwitchChord(1);
+
+    await waitFor(() => {
+      expect(KGPianoRollState.instance().getCurrentHoveredChordGuideCandidate()).toMatchObject({
+        name: expectedCandidates[1].item.name,
+        resolvedNotes: expectedCandidates[1].item.resolvedNotes,
+        note: expectedCandidates[1].item.note,
+      });
+    });
+
+    fireEvent.mouseLeave(pianoGrid);
+
+    await waitFor(() => {
+      expect(KGPianoRollState.instance().getCurrentHoveredChordGuideCandidate()).toBeNull();
+    });
+  });
+});
diff --git a/src/components/piano-roll/PianoRoll.tsx b/src/components/piano-roll/PianoRoll.tsx
index 0ed991f..a8cf32e 100644
--- a/src/components/piano-roll/PianoRoll.tsx
+++ b/src/components/piano-roll/PianoRoll.tsx
@@ -741,6 +741,7 @@ const PianoRoll: React.FC<PianoRollProps> = ({
       // Disabled - clear chord data
       pianoRollState.setCurrentSuitableChords([]);
       pianoRollState.setCurrentSuitableChordsPitchClasses({});
+      pianoRollState.setCurrentHoveredChordGuideCandidate(null);
 
       if (DEBUG_MODE.PIANO_ROLL) {
         console.log(`Chord guide disabled - cleared suitable chords`);
@@ -756,6 +757,7 @@ const PianoRoll: React.FC<PianoRollProps> = ({
       // Update piano roll state
       pianoRollState.setCurrentSuitableChords(suitableChords);
       pianoRollState.setCurrentSuitableChordsPitchClasses(chordsPitchClasses);
+      pianoRollState.setCurrentHoveredChordGuideCandidate(null);
 
       if (DEBUG_MODE.PIANO_ROLL) {
         console.log(`Chord guide updated: ${chordGuide} (${functionType})`);
diff --git a/src/components/settings/Settings.css b/src/components/settings/Settings.css
index 03c66ce..797e730 100644
--- a/src/components/settings/Settings.css
+++ b/src/components/settings/Settings.css
@@ -319,6 +319,28 @@
   margin-bottom: 8px;
 }
 
+.settings-chord-guide-reset-row {
+  justify-content: flex-end;
+}
+
+.settings-chord-guide-toolbar {
+  margin-top: 10px;
+  margin-bottom: 12px;
+}
+
+.settings-chord-guide-toolbar .event-list-toolbar-group:first-child {
+  gap: 8px;
+}
+
+.settings-chord-guide-toolbar .settings-chord-guide-add-button {
+  border: 1px solid #444;
+  border-radius: 3px;
+}
+
+.settings-chord-guide-toolbar .settings-chord-guide-add-button:hover {
+  border: 1px solid #5a5a5a;
+}
+
 button.settings-help {
   color: #5a9fd4;
   text-decoration: underline;
diff --git a/src/components/settings/sections/ChordGuideSettings.test.tsx b/src/components/settings/sections/ChordGuideSettings.test.tsx
index 154b455..d53b92b 100644
--- a/src/components/settings/sections/ChordGuideSettings.test.tsx
+++ b/src/components/settings/sections/ChordGuideSettings.test.tsx
@@ -1,10 +1,15 @@
 import React from 'react';
-import { render, screen } from '@testing-library/react';
+import { fireEvent, render, screen, waitFor, within } from '@testing-library/react';
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 import ChordGuideSettings from './ChordGuideSettings';
+import chordGuideDataJson from '../../../../public/resources/modes/chord_guide.json';
+import type { ChordGuideData } from '../../../core/ChordGuideTypes';
 
+const chordGuideData = chordGuideDataJson as ChordGuideData;
+
+const showAlertMock = vi.fn();
 const configState = new Map<string, unknown>([
-  ['chord_guide.chord_definition', ''],
+  ['chord_guide.custom_items', null],
 ]);
 
 const configManagerMock = {
@@ -22,38 +27,178 @@ vi.mock('../../../core/config/ConfigManager', () => ({
   },
 }));
 
-vi.mock('../../../util/scaleUtil', async () => {
-  const actual = await vi.importActual<typeof import('../../../util/scaleUtil')>('../../../util/scaleUtil');
-  return {
-    ...actual,
-    validateFunctionalChordsJSON: vi.fn(() => ({ valid: true, errors: [] })),
-  };
-});
-
 vi.mock('../../../util/dialogUtil', () => ({
-  showAlert: vi.fn(),
+  showAlert: (...args: unknown[]) => showAlertMock(...args),
 }));
 
 vi.mock('../../../core/KGCore', () => ({
   KGCore: {
-    ORIGINAL_FUNCTIONAL_CHORDS_DATA: {},
-    FUNCTIONAL_CHORDS_DATA: {},
+    CHORD_GUIDE_DATA: {
+      ionian: { T: [], S: [], D: [] },
+      aeolian: { T: [], S: [], D: [] },
+    },
   },
 }));
 
 describe('ChordGuideSettings', () => {
+  const getGroup = (heading: 'Major Candidate Chords' | 'Minor Candidate Chords') => (
+    screen.getByText(heading).closest('.settings-group') as HTMLElement
+  );
+
   beforeEach(() => {
-    configState.set('chord_guide.chord_definition', '');
+    configState.set('chord_guide.custom_items', null);
     configManagerMock.get.mockClear();
     configManagerMock.set.mockClear();
+    showAlertMock.mockClear();
+
+    vi.stubGlobal('fetch', vi.fn(async (input: string | URL | Request) => {
+      const url = String(input);
+      if (url.includes('resources/modes/chord_guide.json')) {
+        return {
+          ok: true,
+          status: 200,
+          json: async () => structuredClone(chordGuideData),
+        };
+      }
+      throw new Error(`Unexpected fetch: ${url}`);
+    }));
   });
 
-  it('renders the legacy notice for chord guide definitions', async () => {
+  it('renders major and minor groups with base-key guidance', async () => {
     render(<ChordGuideSettings />);
 
-    expect(await screen.findByText('Legacy Chord Definition')).toBeTruthy();
-    expect(
-      screen.getByText(/no longer affects chord-guide suggestions in the piano roll/i)
-    ).toBeTruthy();
+    expect(await screen.findByText('Major Candidate Chords')).toBeTruthy();
+    expect(screen.getByText('Minor Candidate Chords')).toBeTruthy();
+    expect(screen.getByText(/relative to C major/i)).toBeTruthy();
+    expect(screen.getByText(/relative to A minor/i)).toBeTruthy();
+  });
+
+  it('switches T/S/D tabs as a mutex control', async () => {
+    render(<ChordGuideSettings />);
+
+    await screen.findByText('Major Candidate Chords');
+    const majorGroup = getGroup('Major Candidate Chords');
+
+    expect(within(majorGroup).getByTitle('C')).toBeTruthy();
+    fireEvent.click(within(majorGroup).getByRole('button', { name: 'S' }));
+
+    expect(within(majorGroup).getByTitle('Fmaj7')).toBeTruthy();
+    expect(within(majorGroup).queryByTitle('Cmaj7')).toBeNull();
+  });
+
+  it('adds and deletes rows in the active table', async () => {
+    render(<ChordGuideSettings />);
+
+    await screen.findByText('Major Candidate Chords');
+    const addButtons = screen.getAllByTitle(/Add .* chord/);
+    fireEvent.click(addButtons[0]);
+
+    await waitFor(() => {
+      expect(configManagerMock.set).toHaveBeenCalledWith(
+        'chord_guide.custom_items',
+        expect.objectContaining({
+          major: expect.objectContaining({
+            T: expect.arrayContaining([expect.objectContaining({ name: 'C' })]),
+          }),
+        })
+      );
+    });
+
+    const rows = screen.getAllByRole('row');
+    fireEvent.click(rows[1]);
+    const deleteButtons = screen.getAllByTitle('Delete selected rows');
+    fireEvent.click(deleteButtons[0]);
+
+    await waitFor(() => {
+      expect(configManagerMock.set).toHaveBeenCalledTimes(2);
+    });
+  });
+
+  it('updates notes and source after a valid chord edit', async () => {
+    render(<ChordGuideSettings />);
+
+    await screen.findByText('Major Candidate Chords');
+    const majorGroup = getGroup('Major Candidate Chords');
+    fireEvent.click(within(majorGroup).getByRole('button', { name: 'S' }));
+
+    const chordCell = within(majorGroup).getByTitle('F');
+    fireEvent.doubleClick(chordCell);
+    const input = screen.getByDisplayValue('F');
+    fireEvent.change(input, { target: { value: 'D7' } });
+    fireEvent.keyDown(input, { key: 'Enter' });
+
+    await waitFor(() => {
+      const saved = configManagerMock.set.mock.calls.at(-1)?.[1] as {
+        major: { S: Array<{ name: string; notes: string[]; source: string }> };
+      };
+      expect(saved.major.S[0]).toMatchObject({
+        name: 'D7',
+        notes: ['D', 'F#', 'A', 'C'],
+        source: 'Non-Diatonic',
+      });
+    });
+  });
+
+  it('rejects invalid chord edits', async () => {
+    render(<ChordGuideSettings />);
+
+    await screen.findByText('Major Candidate Chords');
+    const chordCell = screen.getAllByTitle('C')[0];
+    fireEvent.doubleClick(chordCell);
+    const input = screen.getByDisplayValue('C');
+    fireEvent.change(input, { target: { value: 'invalid' } });
+    fireEvent.keyDown(input, { key: 'Enter' });
+
+    await waitFor(() => {
+      expect(showAlertMock).toHaveBeenCalledWith(expect.stringContaining('valid chord symbol'));
+    });
+  });
+
+  it('enforces the 128-character note limit', async () => {
+    render(<ChordGuideSettings />);
+
+    await screen.findByText('Major Candidate Chords');
+    const noteCell = screen.getAllByRole('cell').find((cell) => cell.textContent === chordGuideData.ionian.T[0].note) as HTMLElement;
+    fireEvent.doubleClick(noteCell);
+    const input = screen.getByDisplayValue(chordGuideData.ionian.T[0].note);
+    fireEvent.change(input, { target: { value: 'x'.repeat(200) } });
+    fireEvent.keyDown(input, { key: 'Enter' });
+
+    await waitFor(() => {
+      const saved = configManagerMock.set.mock.calls.at(-1)?.[1] as { major: { T: Array<{ note: string }> } };
+      expect(saved.major.T[0].note).toHaveLength(128);
+    });
+  });
+
+  it('resets back to bundled defaults', async () => {
+    const customItems = structuredClone(chordGuideData);
+    customItems.ionian.T = [{
+      name: 'G',
+      notes: ['G', 'B', 'D'],
+      source: 'Diatonic',
+      note: 'custom',
+    }];
+    configState.set('chord_guide.custom_items', {
+      major: {
+        T: customItems.ionian.T,
+        S: customItems.ionian.S,
+        D: customItems.ionian.D,
+      },
+      minor: {
+        T: customItems.aeolian.T,
+        S: customItems.aeolian.S,
+        D: customItems.aeolian.D,
+      },
+    });
+
+    render(<ChordGuideSettings />);
+
+    expect((await screen.findAllByTitle('G')).length).toBeGreaterThan(0);
+    fireEvent.click(screen.getByText('Reset to Default'));
+
+    await waitFor(() => {
+      expect(configManagerMock.set).toHaveBeenCalledWith('chord_guide.custom_items', null);
+      expect(screen.getAllByTitle('C')[0]).toBeTruthy();
+    });
   });
 });
diff --git a/src/components/settings/sections/ChordGuideSettings.tsx b/src/components/settings/sections/ChordGuideSettings.tsx
index 97761ff..9f7fe38 100644
--- a/src/components/settings/sections/ChordGuideSettings.tsx
+++ b/src/components/settings/sections/ChordGuideSettings.tsx
@@ -1,108 +1,415 @@
-import React, { useState, useEffect, useCallback } from 'react';
+import React from 'react';
+import { FaPlus, FaTrash } from 'react-icons/fa';
+import '../../EventListPanel.css';
 import { ConfigManager } from '../../../core/config/ConfigManager';
-import { validateFunctionalChordsJSON } from '../../../util/scaleUtil';
 import { KGCore } from '../../../core/KGCore';
+import type {
+  ChordGuideCustomConfig,
+  ChordGuideData,
+  ChordGuideGroupKey,
+  ChordGuideItem,
+  ChordGuideModeDefinition,
+} from '../../../core/ChordGuideTypes';
+import {
+  buildChordGuideCustomConfigFromData,
+  buildChordGuideDataFromDefaultsAndConfig,
+  buildDerivedChordGuideItem,
+  createDefaultChordForGroup,
+} from '../../../util/chordGuideConfigUtil';
+import { parseChordSymbol } from '../../../util/chordUtil';
 import { showAlert } from '../../../util/dialogUtil';
+import { isModifierKeyPressed } from '../../../util/osUtil';
+
+type FunctionType = 'T' | 'S' | 'D';
+type EditableColumn = 'name' | 'note';
+
+interface EditingCell {
+  group: ChordGuideGroupKey;
+  rowIndex: number;
+  column: EditableColumn;
+  value: string;
+}
+
+const FUNCTION_BUTTONS: Array<{ value: FunctionType; label: string; title: string }> = [
+  { value: 'T', label: 'T', title: 'Tonic' },
+  { value: 'S', label: 'S', title: 'Subdominant' },
+  { value: 'D', label: 'D', title: 'Dominant' },
+];
+
+const GROUP_LABELS: Record<ChordGuideGroupKey, string> = {
+  major: 'Major Candidate Chords',
+  minor: 'Minor Candidate Chords',
+};
+
+const GROUP_HELP: Record<ChordGuideGroupKey, string> = {
+  major: 'Enter chords relative to C major. The app will transpose them automatically for other major key signatures.',
+  minor: 'Enter chords relative to A minor. The app will transpose them automatically for other minor key signatures.',
+};
+
+const CONFIG_KEY = 'chord_guide.custom_items';
+
+function cloneModeDefinition(definition: ChordGuideModeDefinition): ChordGuideModeDefinition {
+  return {
+    T: definition.T.map((item) => ({ ...item, notes: [...item.notes] })),
+    S: definition.S.map((item) => ({ ...item, notes: [...item.notes] })),
+    D: definition.D.map((item) => ({ ...item, notes: [...item.notes] })),
+  };
+}
+
+function cloneCustomConfig(config: ChordGuideCustomConfig): ChordGuideCustomConfig {
+  return {
+    major: cloneModeDefinition(config.major),
+    minor: cloneModeDefinition(config.minor),
+  };
+}
+
+function getModeDefinition(config: ChordGuideCustomConfig, group: ChordGuideGroupKey): ChordGuideModeDefinition {
+  return group === 'major' ? config.major : config.minor;
+}
+
+function setModeDefinition(
+  config: ChordGuideCustomConfig,
+  group: ChordGuideGroupKey,
+  definition: ChordGuideModeDefinition,
+): ChordGuideCustomConfig {
+  return group === 'major'
+    ? { ...config, major: definition }
+    : { ...config, minor: definition };
+}
+
+async function loadBundledChordGuideData(): Promise<ChordGuideData> {
+  const response = await fetch(`${import.meta.env.BASE_URL}resources/modes/chord_guide.json`);
+  if (!response.ok) {
+    throw new Error(`Failed to fetch chord_guide.json: ${response.status}`);
+  }
+  return response.json() as Promise<ChordGuideData>;
+}
 
 const ChordGuideSettings: React.FC = () => {
-  const [chordDefinition, setChordDefinition] = useState<string>('');
-  const [validationErrors, setValidationErrors] = useState<string[]>([]);
-
   const configManager = ConfigManager.instance();
+  const [defaultsData, setDefaultsData] = React.useState<ChordGuideData | null>(null);
+  const [customConfig, setCustomConfig] = React.useState<ChordGuideCustomConfig | null>(null);
+  const [activeFunctions, setActiveFunctions] = React.useState<Record<ChordGuideGroupKey, FunctionType>>({
+    major: 'T',
+    minor: 'T',
+  });
+  const [selectedRows, setSelectedRows] = React.useState<Record<ChordGuideGroupKey, Set<number>>>({
+    major: new Set(),
+    minor: new Set(),
+  });
+  const [editingCell, setEditingCell] = React.useState<EditingCell | null>(null);
+  const editInputRef = React.useRef<HTMLInputElement | null>(null);
+  const previousEditingCellKeyRef = React.useRef<string | null>(null);
 
-  // Load configuration values on component mount
-  useEffect(() => {
-    const loadConfig = async () => {
+  React.useEffect(() => {
+    const initialize = async () => {
       if (!configManager.getIsInitialized()) {
         await configManager.initialize();
       }
 
-      setChordDefinition((configManager.get('chord_guide.chord_definition') as string) || '');
+      const bundledData = await loadBundledChordGuideData();
+      const persisted = configManager.get(CONFIG_KEY) as ChordGuideCustomConfig | null | undefined;
+      setDefaultsData(bundledData);
+      setCustomConfig(persisted ? cloneCustomConfig(persisted) : buildChordGuideCustomConfigFromData(bundledData));
     };
 
-    loadConfig();
+    void initialize().catch((error) => {
+      console.error('Failed to initialize chord guide settings:', error);
+      void showAlert('Failed to load chord guide settings.');
+    });
   }, [configManager]);
 
-  // Debounced save function for textarea
-  const debouncedSave = useCallback((value: string) => {
-    const timeoutId = setTimeout(async () => {
-      try {
-        await configManager.set('chord_guide.chord_definition', value);
-        console.log('Chord definition saved');
-      } catch (error) {
-        console.error('Failed to save chord definition:', error);
+  React.useEffect(() => {
+    if (!editingCell) {
+      previousEditingCellKeyRef.current = null;
+      return;
+    }
+
+    const editingCellKey = `${editingCell.group}-${editingCell.rowIndex}-${editingCell.column}`;
+    if (previousEditingCellKeyRef.current === editingCellKey) {
+      return;
+    }
+    previousEditingCellKeyRef.current = editingCellKey;
+
+    editInputRef.current?.focus();
+    editInputRef.current?.select();
+  }, [editingCell]);
+
+  const persistCustomConfig = React.useCallback(async (nextConfig: ChordGuideCustomConfig, persistValue: ChordGuideCustomConfig | null = nextConfig) => {
+    if (!defaultsData) {
+      return;
+    }
+    const cloned = cloneCustomConfig(nextConfig);
+    setCustomConfig(cloned);
+    KGCore.CHORD_GUIDE_DATA = buildChordGuideDataFromDefaultsAndConfig(defaultsData, cloned);
+    await configManager.set(CONFIG_KEY, persistValue ? cloneCustomConfig(persistValue) : null);
+  }, [configManager, defaultsData]);
+
+  const updateGroupRows = React.useCallback(async (
+    group: ChordGuideGroupKey,
+    functionType: FunctionType,
+    updater: (rows: ChordGuideItem[]) => ChordGuideItem[],
+  ) => {
+    if (!customConfig) {
+      return;
+    }
+    const nextConfig = cloneCustomConfig(customConfig);
+    const modeDefinition = getModeDefinition(nextConfig, group);
+    const nextDefinition: ChordGuideModeDefinition = {
+      ...modeDefinition,
+      [functionType]: updater(modeDefinition[functionType]),
+    };
+    const updatedConfig = setModeDefinition(nextConfig, group, nextDefinition);
+    await persistCustomConfig(updatedConfig);
+  }, [customConfig, persistCustomConfig]);
+
+  const commitEditingCell = React.useCallback(async () => {
+    if (!editingCell || !customConfig) {
+      return;
+    }
+
+    const { group, rowIndex, column } = editingCell;
+    const functionType = activeFunctions[group];
+    const modeDefinition = getModeDefinition(customConfig, group);
+    const row = modeDefinition[functionType][rowIndex];
+    if (!row) {
+      setEditingCell(null);
+      return;
+    }
+
+    const trimmedValue = editingCell.value.trim();
+    if (column === 'name') {
+      if (!trimmedValue || parseChordSymbol(trimmedValue) === null) {
+        await showAlert('Please enter a valid chord symbol. Example: Bm7b5');
+        return;
       }
-    }, 1000); // 1 second debounce for longer text
+      const derived = buildDerivedChordGuideItem(group, { name: trimmedValue, note: row.note });
+      if (!derived) {
+        await showAlert('Unable to derive notes for this chord. Please use a supported chord symbol.');
+        return;
+      }
+      await updateGroupRows(group, functionType, (rows) => rows.map((candidate, index) => (
+        index === rowIndex
+          ? { ...derived, roman: undefined }
+          : candidate
+      )));
+    } else {
+      await updateGroupRows(group, functionType, (rows) => rows.map((candidate, index) => (
+        index === rowIndex
+          ? { ...candidate, note: trimmedValue.slice(0, 128) }
+          : candidate
+      )));
+    }
 
-    return () => clearTimeout(timeoutId);
-  }, [configManager]);
+    setEditingCell(null);
+  }, [activeFunctions, customConfig, editingCell, updateGroupRows]);
 
-  // Save configuration when value changes
-  const handleChordDefinitionChange = (value: string) => {
-    setChordDefinition(value);
+  const handleEditInputBlur = () => {
+    void commitEditingCell();
+  };
 
-    // Validate the JSON
-    if (value.trim()) {
-      const validationResult = validateFunctionalChordsJSON(value);
-      setValidationErrors(validationResult.valid ? [] : validationResult.errors);
+  const handleEditInputKeyDown = (event: React.KeyboardEvent<HTMLInputElement>) => {
+    event.stopPropagation();
+    if (event.key === 'Enter') {
+      event.preventDefault();
+      void commitEditingCell();
+    }
+    if (event.key === 'Escape') {
+      event.preventDefault();
+      setEditingCell(null);
+    }
+  };
 
-      // Update FUNCTIONAL_CHORDS_DATA if valid and non-empty
-      if (validationResult.valid) {
-        try {
-          KGCore.FUNCTIONAL_CHORDS_DATA = JSON.parse(value);
-          console.log('Applied custom chord definition');
-        } catch (error) {
-          console.error('Failed to parse chord definition:', error);
-          KGCore.FUNCTIONAL_CHORDS_DATA = KGCore.ORIGINAL_FUNCTIONAL_CHORDS_DATA;
-        }
+  const handleRowClick = (
+    group: ChordGuideGroupKey,
+    rowIndex: number,
+    event: React.MouseEvent<HTMLTableRowElement>,
+  ) => {
+    event.stopPropagation();
+    if (editingCell) {
+      return;
+    }
+
+    const nextSelected = new Set(selectedRows[group]);
+    if (isModifierKeyPressed(event)) {
+      if (nextSelected.has(rowIndex)) {
+        nextSelected.delete(rowIndex);
       } else {
-        // Revert to original if invalid
-        KGCore.FUNCTIONAL_CHORDS_DATA = KGCore.ORIGINAL_FUNCTIONAL_CHORDS_DATA;
-        console.log('Invalid chord definition, reverted to original');
+        nextSelected.add(rowIndex);
       }
     } else {
-      setValidationErrors([]);
-      // Revert to original if empty
-      KGCore.FUNCTIONAL_CHORDS_DATA = KGCore.ORIGINAL_FUNCTIONAL_CHORDS_DATA;
-      console.log('Chord definition cleared, reverted to original');
+      nextSelected.clear();
+      nextSelected.add(rowIndex);
     }
 
-    debouncedSave(value);
+    setSelectedRows((previous) => ({ ...previous, [group]: nextSelected }));
   };
 
-  // Load default template from functional_chords.json (preserving original formatting)
-  const handleLoadDefaultTemplate = async () => {
-    try {
-      const response = await fetch(`${import.meta.env.BASE_URL}resources/modes/functional_chords.json`);
-      if (!response.ok) {
-        throw new Error(`Failed to fetch functional_chords.json: ${response.status}`);
-      }
-      // Get the raw text to preserve original formatting
-      const rawText = await response.text();
-      setChordDefinition(rawText);
-      setValidationErrors([]); // Clear errors when loading valid template
-      await configManager.set('chord_guide.chord_definition', rawText);
-
-      // Revert to original if empty
-      KGCore.FUNCTIONAL_CHORDS_DATA = KGCore.ORIGINAL_FUNCTIONAL_CHORDS_DATA;
-
-      console.log('Loaded default chord template');
-    } catch (error) {
-      console.error('Failed to load default template:', error);
-      await showAlert('Failed to load default template. Please check the console for details.');
+  const handleTableBackgroundMouseDown = (group: ChordGuideGroupKey, event: React.MouseEvent<HTMLDivElement>) => {
+    if (event.target !== event.currentTarget) {
+      return;
     }
+    setSelectedRows((previous) => ({ ...previous, [group]: new Set() }));
   };
 
-  // Clear the chord definition
-  const handleClear = async () => {
-    setChordDefinition('');
-    setValidationErrors([]); // Clear errors when clearing
-    await configManager.set('chord_guide.chord_definition', '');
+  const handleAddRow = async (group: ChordGuideGroupKey) => {
+    const functionType = activeFunctions[group];
+    const defaultChord = createDefaultChordForGroup(group);
+    await updateGroupRows(group, functionType, (rows) => [...rows, { ...defaultChord, roman: undefined }]);
+    setSelectedRows((previous) => ({ ...previous, [group]: new Set([getModeDefinition(customConfig!, group)[functionType].length]) }));
+  };
 
-    // Revert to original if empty
-    KGCore.FUNCTIONAL_CHORDS_DATA = KGCore.ORIGINAL_FUNCTIONAL_CHORDS_DATA;
-    
-    console.log('Chord definition cleared');
+  const handleDeleteRows = async (group: ChordGuideGroupKey) => {
+    const selection = selectedRows[group];
+    if (selection.size === 0) {
+      return;
+    }
+    const functionType = activeFunctions[group];
+    await updateGroupRows(group, functionType, (rows) => rows.filter((_, index) => !selection.has(index)));
+    setSelectedRows((previous) => ({ ...previous, [group]: new Set() }));
+  };
+
+  const handleResetToDefault = async () => {
+    if (!defaultsData) {
+      return;
+    }
+    const resetConfig = buildChordGuideCustomConfigFromData(defaultsData);
+    setEditingCell(null);
+    setSelectedRows({ major: new Set(), minor: new Set() });
+    setCustomConfig(resetConfig);
+    KGCore.CHORD_GUIDE_DATA = buildChordGuideDataFromDefaultsAndConfig(defaultsData, resetConfig);
+    await configManager.set(CONFIG_KEY, null);
+  };
+
+  const renderGroup = (group: ChordGuideGroupKey) => {
+    if (!customConfig) {
+      return null;
+    }
+
+    const functionType = activeFunctions[group];
+    const rows = getModeDefinition(customConfig, group)[functionType];
+    const selection = selectedRows[group];
+
+    return (
+      <div className="settings-group" key={group}>
+        <div className="settings-group-header">
+          <h4>{GROUP_LABELS[group]}</h4>
+        </div>
+        <div className="settings-description">{GROUP_HELP[group]}</div>
+
+        <div className="event-list-tabs" role="tablist" aria-label={`${GROUP_LABELS[group]} functions`}>
+          {FUNCTION_BUTTONS.map((button) => (
+            <button
+              key={button.value}
+              className={`event-list-tab${functionType === button.value ? ' active' : ''}`}
+              type="button"
+              title={button.title}
+              onClick={() => {
+                setActiveFunctions((previous) => ({ ...previous, [group]: button.value }));
+                setSelectedRows((previous) => ({ ...previous, [group]: new Set() }));
+                setEditingCell(null);
+              }}
+            >
+              {button.label}
+            </button>
+          ))}
+        </div>
+
+        <div className="event-list-toolbar settings-chord-guide-toolbar">
+          <div className="event-list-toolbar-group">
+            <button
+              className="event-list-add-button settings-chord-guide-add-button"
+              title={`Add ${GROUP_LABELS[group]} chord`}
+              type="button"
+              onClick={() => { void handleAddRow(group); }}
+            >
+              <FaPlus />
+            </button>
+          </div>
+          <div className="event-list-toolbar-group event-list-toolbar-group-right">
+            <button
+              className="event-list-delete-button"
+              title="Delete selected rows"
+              type="button"
+              onClick={() => { void handleDeleteRows(group); }}
+              disabled={selection.size === 0}
+            >
+              <FaTrash />
+            </button>
+          </div>
+        </div>
+
+        <div className="event-list-table-shell" onMouseDown={(event) => handleTableBackgroundMouseDown(group, event)}>
+          <table className="event-list-table">
+            <thead>
+              <tr>
+                <th>Chord</th>
+                <th>Notes</th>
+                <th>Source</th>
+                <th>Note</th>
+              </tr>
+            </thead>
+            <tbody>
+              {rows.map((row, rowIndex) => {
+                const isEditingName = editingCell?.group === group && editingCell.rowIndex === rowIndex && editingCell.column === 'name';
+                const isEditingNote = editingCell?.group === group && editingCell.rowIndex === rowIndex && editingCell.column === 'note';
+                return (
+                  <tr
+                    key={`${group}-${functionType}-${rowIndex}-${row.name}`}
+                    className={selection.has(rowIndex) ? 'selected' : ''}
+                    onClick={(event) => handleRowClick(group, rowIndex, event)}
+                  >
+                    <td
+                      title={row.name}
+                      onDoubleClick={(event) => {
+                        event.stopPropagation();
+                        setEditingCell({ group, rowIndex, column: 'name', value: row.name });
+                      }}
+                    >
+                      {isEditingName ? (
+                        <input
+                          ref={editInputRef}
+                          className="event-list-cell-input"
+                          value={editingCell.value}
+                          onChange={(event) => setEditingCell({ ...editingCell, value: event.target.value })}
+                          onBlur={handleEditInputBlur}
+                          onClick={(event) => event.stopPropagation()}
+                          onDoubleClick={(event) => event.stopPropagation()}
+                          onKeyDown={handleEditInputKeyDown}
+                        />
+                      ) : row.name}
+                    </td>
+                    <td title={row.notes.join(' ')}>{row.notes.join(' ')}</td>
+                    <td title={row.source}>{row.source}</td>
+                    <td
+                      title={row.note}
+                      onDoubleClick={(event) => {
+                        event.stopPropagation();
+                        setEditingCell({ group, rowIndex, column: 'note', value: row.note });
+                      }}
+                    >
+                      {isEditingNote ? (
+                        <input
+                          ref={editInputRef}
+                          className="event-list-cell-input"
+                          maxLength={128}
+                          value={editingCell.value}
+                          onChange={(event) => setEditingCell({ ...editingCell, value: event.target.value.slice(0, 128) })}
+                          onBlur={handleEditInputBlur}
+                          onClick={(event) => event.stopPropagation()}
+                          onDoubleClick={(event) => event.stopPropagation()}
+                          onKeyDown={handleEditInputKeyDown}
+                        />
+                      ) : row.note}
+                    </td>
+                  </tr>
+                );
+              })}
+            </tbody>
+          </table>
+        </div>
+      </div>
+    );
   };
 
   return (
@@ -112,45 +419,13 @@ const ChordGuideSettings: React.FC = () => {
       </div>
 
       <div className="settings-section-content">
-        <div className="settings-group">
-          <h4>Legacy Chord Definition</h4>
-          <div className="settings-help" style={{ fontSize: '12px', color: '#888', marginBottom: '8px' }}>
-            This editor is kept for legacy mode and highlighting behavior. It no longer affects chord-guide suggestions in the piano roll.
-          </div>
-          <div className="settings-help-links">
-            <button
-              className="settings-help"
-              onClick={handleLoadDefaultTemplate}
-            >
-              Load Default Template
-            </button>
-            <button
-              className="settings-help"
-              onClick={handleClear}
-            >
-              Clear
-            </button>
-          </div>
-
-          <div className="settings-item">
-            <textarea
-              className="settings-textarea"
-              placeholder="Please input your legacy chord definitions"
-              rows={8}
-              value={chordDefinition}
-              onChange={(e) => handleChordDefinitionChange(e.target.value)}
-            />
-            {validationErrors.length > 0 && (
-              <div className="settings-validation-errors">
-                {validationErrors.map((error, index) => (
-                  <div key={index} className="settings-validation-error">
-                    {error}
-                  </div>
-                ))}
-              </div>
-            )}
-          </div>
+        <div className="settings-help-links settings-chord-guide-reset-row">
+          <button className="settings-help" type="button" onClick={() => { void handleResetToDefault(); }}>
+            Reset to Default
+          </button>
         </div>
+        {renderGroup('major')}
+        {renderGroup('minor')}
       </div>
     </div>
   );
diff --git a/src/core/ChordGuideTypes.ts b/src/core/ChordGuideTypes.ts
index 19e1a28..a4afe32 100644
--- a/src/core/ChordGuideTypes.ts
+++ b/src/core/ChordGuideTypes.ts
@@ -1,8 +1,10 @@
+export type ChordGuideSource = 'Diatonic' | 'Non-Diatonic';
+
 export interface ChordGuideItem {
   name: string;
-  roman: string;
+  roman?: string;
   notes: string[];
-  source: string;
+  source: ChordGuideSource;
   note: string;
 }
 
@@ -21,3 +23,10 @@ export interface ResolvedChordGuideItem extends ChordGuideItem {
   resolvedNotes: string[];
   pitchClasses: number[];
 }
+
+export type ChordGuideGroupKey = 'major' | 'minor';
+
+export interface ChordGuideCustomConfig {
+  major: ChordGuideModeDefinition;
+  minor: ChordGuideModeDefinition;
+}
diff --git a/src/core/config/ConfigManager.ts b/src/core/config/ConfigManager.ts
index b7c3702..c61f447 100644
--- a/src/core/config/ConfigManager.ts
+++ b/src/core/config/ConfigManager.ts
@@ -1,3 +1,4 @@
+import type { ChordGuideCustomConfig } from '../ChordGuideTypes';
 import { KGConfigStorage } from '../io/KGConfigStorage';
 
 /**
@@ -103,6 +104,7 @@ interface AppConfig {
   };
   chord_guide: {
     chord_definition: string;
+    custom_items: ChordGuideCustomConfig | null;
   };
   [key: string]: unknown;
 }
@@ -300,7 +302,8 @@ export class ConfigManager {
           custom_instructions: ''
         },
         chord_guide: {
-          chord_definition: ''
+          chord_definition: '',
+          custom_items: null,
         }
       };
       console.log('Using fallback hardcoded config due to load error');
diff --git a/src/core/state/KGPianoRollState.ts b/src/core/state/KGPianoRollState.ts
index 50c3969..c2d2753 100644
--- a/src/core/state/KGPianoRollState.ts
+++ b/src/core/state/KGPianoRollState.ts
@@ -28,6 +28,8 @@ export class KGPianoRollState {
   private currentMatchingChords: number[][] = [];
   private currentSelectedChordIndex: number = 0;
   private currentChordCursorPitch: number | null = null;
+  private currentHoveredChordGuideCandidate: ResolvedChordGuideItem | null = null;
+  private listeners = new Set<() => void>();
 
   private constructor() {
     console.log("KGPianoRollState initialized");
@@ -143,6 +145,7 @@ export class KGPianoRollState {
 
   public setCurrentMatchingChords(chords: number[][]): void {
     this.currentMatchingChords = chords;
+    this.emitChange();
   }
 
   public getCurrentSelectedChordIndex(): number {
@@ -151,6 +154,7 @@ export class KGPianoRollState {
 
   public setCurrentSelectedChordIndex(index: number): void {
     this.currentSelectedChordIndex = index;
+    this.emitChange();
   }
 
   public getCurrentChordCursorPitch(): number | null {
@@ -159,5 +163,26 @@ export class KGPianoRollState {
 
   public setCurrentChordCursorPitch(pitch: number | null): void {
     this.currentChordCursorPitch = pitch;
+    this.emitChange();
+  }
+
+  public getCurrentHoveredChordGuideCandidate(): ResolvedChordGuideItem | null {
+    return this.currentHoveredChordGuideCandidate;
+  }
+
+  public setCurrentHoveredChordGuideCandidate(candidate: ResolvedChordGuideItem | null): void {
+    this.currentHoveredChordGuideCandidate = candidate;
+    this.emitChange();
+  }
+
+  public subscribe(listener: () => void): () => void {
+    this.listeners.add(listener);
+    return () => {
+      this.listeners.delete(listener);
+    };
+  }
+
+  private emitChange(): void {
+    this.listeners.forEach((listener) => listener());
   }
 }
diff --git a/src/util/chordGuideConfigUtil.test.ts b/src/util/chordGuideConfigUtil.test.ts
new file mode 100644
index 0000000..918038e
--- /dev/null
+++ b/src/util/chordGuideConfigUtil.test.ts
@@ -0,0 +1,70 @@
+import { describe, expect, it } from 'vitest';
+import chordGuideDataJson from '../../public/resources/modes/chord_guide.json';
+import type { ChordGuideData } from '../core/ChordGuideTypes';
+import {
+  buildChordGuideCustomConfigFromData,
+  buildChordGuideDataFromDefaultsAndConfig,
+  buildDerivedChordGuideItem,
+  createDefaultChordForGroup,
+  deriveChordGuideNotes,
+  deriveChordGuideSource,
+} from './chordGuideConfigUtil';
+
+const chordGuideData = chordGuideDataJson as ChordGuideData;
+
+describe('chordGuideConfigUtil', () => {
+  it('derives canonical note names from a chord symbol', () => {
+    expect(deriveChordGuideNotes('Dm7')).toEqual(['D', 'F', 'A', 'C']);
+    expect(deriveChordGuideNotes('Eaug')).toEqual(['E', 'G#', 'C']);
+  });
+
+  it('classifies major-group diatonic and non-diatonic chords', () => {
+    expect(deriveChordGuideSource('Dm7', 'major')).toBe('Diatonic');
+    expect(deriveChordGuideSource('Bb', 'major')).toBe('Non-Diatonic');
+    expect(deriveChordGuideSource('D7', 'major')).toBe('Non-Diatonic');
+  });
+
+  it('classifies minor-group borrowed chords as non-diatonic', () => {
+    expect(deriveChordGuideSource('Am', 'minor')).toBe('Diatonic');
+    expect(deriveChordGuideSource('E7', 'minor')).toBe('Non-Diatonic');
+  });
+
+  it('builds a derived chord guide item with trimmed note text', () => {
+    const result = buildDerivedChordGuideItem('major', {
+      name: 'Cmaj7',
+      note: '  bright tonic  ',
+      roman: 'Imaj7',
+    });
+
+    expect(result).toEqual({
+      name: 'Cmaj7',
+      roman: 'Imaj7',
+      notes: ['C', 'E', 'G', 'B'],
+      source: 'Diatonic',
+      note: 'bright tonic',
+    });
+  });
+
+  it('creates parser-valid default chords for each group', () => {
+    expect(createDefaultChordForGroup('major').name).toBe('C');
+    expect(createDefaultChordForGroup('minor').name).toBe('Am');
+  });
+
+  it('converts bundled defaults into a persisted custom config shape', () => {
+    const result = buildChordGuideCustomConfigFromData(chordGuideData);
+
+    expect(result.major.T[0].name).toBe(chordGuideData.ionian.T[0].name);
+    expect(result.minor.D[0].name).toBe(chordGuideData.aeolian.D[0].name);
+  });
+
+  it('prefers persisted custom config over bundled defaults for runtime data', () => {
+    const custom = buildChordGuideCustomConfigFromData(chordGuideData);
+    custom.major.T = [createDefaultChordForGroup('major')];
+
+    const result = buildChordGuideDataFromDefaultsAndConfig(chordGuideData, custom);
+
+    expect(result.ionian.T).toHaveLength(1);
+    expect(result.ionian.T[0].name).toBe('C');
+    expect(result.aeolian.T[0].name).toBe(chordGuideData.aeolian.T[0].name);
+  });
+});
diff --git a/src/util/chordGuideConfigUtil.ts b/src/util/chordGuideConfigUtil.ts
new file mode 100644
index 0000000..7224610
--- /dev/null
+++ b/src/util/chordGuideConfigUtil.ts
@@ -0,0 +1,115 @@
+import type {
+  ChordGuideCustomConfig,
+  ChordGuideData,
+  ChordGuideGroupKey,
+  ChordGuideItem,
+  ChordGuideModeDefinition,
+  ChordGuideSource,
+} from '../core/ChordGuideTypes';
+import { getChordMidiPitches, parseChordSymbol } from './chordUtil';
+import { noteNameToPitchClass } from './scaleUtil';
+
+const SHARP_NOTE_NAMES = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'];
+const REFERENCE_SCALE_PITCH_CLASSES: Record<ChordGuideGroupKey, number[]> = {
+  major: [0, 2, 4, 5, 7, 9, 11], // C major
+  minor: [9, 11, 0, 2, 4, 5, 7], // A natural minor
+};
+
+function toCanonicalNoteNames(pitches: number[]): string[] {
+  return pitches.map((pitch) => SHARP_NOTE_NAMES[((pitch % 12) + 12) % 12]);
+}
+
+function getReferenceRootMidi(symbol: string): number | null {
+  const descriptor = parseChordSymbol(symbol);
+  if (!descriptor) {
+    return null;
+  }
+  return noteNameToPitchClass(descriptor.root);
+}
+
+export function deriveChordGuideNotes(symbol: string): string[] | null {
+  const rootMidi = getReferenceRootMidi(symbol);
+  if (rootMidi === null) {
+    return null;
+  }
+  const pitches = getChordMidiPitches(symbol, rootMidi);
+  if (pitches.length === 0) {
+    return null;
+  }
+  return toCanonicalNoteNames(pitches);
+}
+
+export function deriveChordGuideSource(symbol: string, group: ChordGuideGroupKey): ChordGuideSource | null {
+  const rootMidi = getReferenceRootMidi(symbol);
+  if (rootMidi === null) {
+    return null;
+  }
+  const pitches = getChordMidiPitches(symbol, rootMidi);
+  if (pitches.length === 0) {
+    return null;
+  }
+
+  const referenceScale = new Set(REFERENCE_SCALE_PITCH_CLASSES[group]);
+  const isDiatonic = pitches.every((pitch) => referenceScale.has(((pitch % 12) + 12) % 12));
+  return isDiatonic ? 'Diatonic' : 'Non-Diatonic';
+}
+
+export function buildDerivedChordGuideItem(
+  group: ChordGuideGroupKey,
+  item: Pick<ChordGuideItem, 'name' | 'note'> & Partial<Pick<ChordGuideItem, 'roman'>>
+): ChordGuideItem | null {
+  const notes = deriveChordGuideNotes(item.name);
+  const source = deriveChordGuideSource(item.name, group);
+  if (!notes || !source) {
+    return null;
+  }
+
+  return {
+    name: item.name,
+    roman: item.roman,
+    notes,
+    source,
+    note: item.note.trim().slice(0, 128),
+  };
+}
+
+function cloneModeDefinition(definition: ChordGuideModeDefinition): ChordGuideModeDefinition {
+  return {
+    T: definition.T.map((item) => ({ ...item, notes: [...item.notes] })),
+    S: definition.S.map((item) => ({ ...item, notes: [...item.notes] })),
+    D: definition.D.map((item) => ({ ...item, notes: [...item.notes] })),
+  };
+}
+
+export function buildChordGuideCustomConfigFromData(data: ChordGuideData): ChordGuideCustomConfig {
+  return {
+    major: cloneModeDefinition(data.ionian),
+    minor: cloneModeDefinition(data.aeolian),
+  };
+}
+
+export function buildChordGuideDataFromDefaultsAndConfig(
+  defaults: ChordGuideData,
+  customConfig: ChordGuideCustomConfig | null | undefined,
+): ChordGuideData {
+  if (!customConfig) {
+    return {
+      ionian: cloneModeDefinition(defaults.ionian),
+      aeolian: cloneModeDefinition(defaults.aeolian),
+    };
+  }
+
+  return {
+    ionian: cloneModeDefinition(customConfig.major),
+    aeolian: cloneModeDefinition(customConfig.minor),
+  };
+}
+
+export function createDefaultChordForGroup(group: ChordGuideGroupKey): ChordGuideItem {
+  const baseName = group === 'minor' ? 'Am' : 'C';
+  const derived = buildDerivedChordGuideItem(group, { name: baseName, note: '' });
+  if (!derived) {
+    throw new Error(`Unable to create default chord for group ${group}`);
+  }
+  return derived;
+}
diff --git a/src/util/chordGuideDataUtil.test.ts b/src/util/chordGuideDataUtil.test.ts
index ef3e0ce..57b6028 100644
--- a/src/util/chordGuideDataUtil.test.ts
+++ b/src/util/chordGuideDataUtil.test.ts
@@ -1,9 +1,12 @@
 import { beforeEach, describe, expect, it } from 'vitest';
 import { Note } from 'tonal';
 import { KGCore } from '../core/KGCore';
+import type { ChordGuideData } from '../core/ChordGuideTypes';
 import { getMatchingChordGuideChordsForPitch, resolveChordGuideItems } from './chordGuideDataUtil';
 import { getChordPitchClasses, parseChordSymbol } from './chordUtil';
-import chordGuideData from '../../public/resources/modes/chord_guide.json';
+import chordGuideDataJson from '../../public/resources/modes/chord_guide.json';
+
+const chordGuideData = chordGuideDataJson as ChordGuideData;
 
 function getExpectedPitchClassesFromNotes(notes: string[]): number[] {
   return notes.map((note) => {
diff --git a/src/util/chordGuideDataUtil.ts b/src/util/chordGuideDataUtil.ts
index a813979..84b85ff 100644
--- a/src/util/chordGuideDataUtil.ts
+++ b/src/util/chordGuideDataUtil.ts
@@ -9,6 +9,12 @@ const SHARP_NOTE_NAMES = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A',
 export type ChordGuideMode = 'ionian' | 'aeolian';
 export type ChordGuideFunctionType = 'T' | 'S' | 'D';
 
+export interface MatchingChordGuideCandidate {
+  item: ResolvedChordGuideItem;
+  matchedPitchIndex: number;
+  displayPitchClasses: number[];
+}
+
 function getReferenceTonic(mode: ChordGuideMode): string {
   return mode === 'aeolian' ? 'A' : 'C';
 }
@@ -85,13 +91,23 @@ export function getMatchingChordGuideChordsForPitch(
   mode: ChordGuideMode,
   functionType: ChordGuideFunctionType
 ): number[][] {
+  return getMatchingChordGuideCandidatesForPitch(hoverPitch, keySignature, mode, functionType)
+    .map((candidate) => candidate.displayPitchClasses);
+}
+
+export function getMatchingChordGuideCandidatesForPitch(
+  hoverPitch: number,
+  keySignature: KeySignature,
+  mode: ChordGuideMode,
+  functionType: ChordGuideFunctionType
+): MatchingChordGuideCandidate[] {
   const resolvedChords = resolveChordGuideItems(keySignature, mode, functionType);
   if (resolvedChords.length === 0) {
     return [];
   }
 
-  const hoverPitchClass = hoverPitch % 12;
-  const matchesByPosition: number[][][] = [];
+  const hoverPitchClass = ((hoverPitch % 12) + 12) % 12;
+  const matchesByPosition: MatchingChordGuideCandidate[][] = [];
 
   for (const item of resolvedChords) {
     for (let i = 0; i < item.pitchClasses.length; i++) {
@@ -103,10 +119,13 @@ export function getMatchingChordGuideChordsForPitch(
         matchesByPosition[i] = [];
       }
 
-      const chord = item.pitchClasses[i] >= 12
-        ? item.pitchClasses.map((pitch) => pitch - 12)
-        : item.pitchClasses;
-      matchesByPosition[i].push(chord);
+      matchesByPosition[i].push({
+        item,
+        matchedPitchIndex: i,
+        displayPitchClasses: item.pitchClasses[i] >= 12
+          ? item.pitchClasses.map((pitch) => pitch - 12)
+          : item.pitchClasses,
+      });
       break;
     }
   }