diff --git a/README.md b/README.md
index a1063b971..6135fe781 100644
--- a/README.md
+++ b/README.md
@@ -256,6 +256,33 @@ PLUGIN_DEV_DIR=../my-plugins          # load plugins from disk instead of ZIPs
 
 `EXTENSION_DIRECTORY_URL` enables the admin marketplace for browsing and installing plugins and themes. `PLUGIN_DEV_DIR` is for plugin authors: each immediate subfolder is one plugin with a `manifest.json`, and an entrypoint under `src/` is bundled on demand with esbuild, so editing sources needs only a browser refresh.
 
+Sandboxed plugins that integrate provider-side labels can use the native
+`api.keywords` facade exposed by `@plugin-host`:
+
+```js
+const api = require('@plugin-host');
+
+const known = await api.keywords.list();                 // settings:read
+const scan = await api.keywords.discover();              // email:read
+const id = Object.keys(scan.keywords)
+  .find((keyword) => keyword.startsWith('$label:'))
+  ?.slice('$label:'.length);
+if (id) {
+  await api.keywords.add([{                              // settings:write
+    id,
+    label: 'Provider label',
+    // color is optional; Bulwark picks a palette colour when omitted
+    visibility: 'show',
+  }]);
+}
+const counts = await api.keywords.refreshCounts();        // email:read
+```
+
+`keywords.add()` is append-only and case-insensitive by id: it returns added
+and skipped definitions without overwriting the user's existing label name,
+colour, visibility, or order. `keywords.discover()` scans the active account's
+JMAP message keywords and reports whether its bounded scan was complete.
+
 </details>
 
 <details>
diff --git a/lib/__tests__/plugin-api-gates.test.ts b/lib/__tests__/plugin-api-gates.test.ts
index abf0f8232..7bb0a7925 100644
--- a/lib/__tests__/plugin-api-gates.test.ts
+++ b/lib/__tests__/plugin-api-gates.test.ts
@@ -1,5 +1,7 @@
-import { describe, it, expect, vi } from 'vitest';
+import { afterEach, describe, it, expect, vi } from 'vitest';
 import type { InstalledPlugin } from '../plugin-types';
+import { useEmailStore } from '@/stores/email-store';
+import { DEFAULT_KEYWORDS, useSettingsStore } from '@/stores/settings-store';
 
 vi.mock('@/stores/toast-store', () => ({
   toast: { success: vi.fn(), error: vi.fn(), info: vi.fn(), warning: vi.fn() },
@@ -93,3 +95,69 @@ describe('method-name typos', () => {
     expect(await gateError(plugin(), 'upfiles.set', ['x'])).toMatch(/Unknown API method/);
   });
 });
+
+describe('native keyword extension API', () => {
+  afterEach(() => {
+    useSettingsStore.setState({ emailKeywords: [...DEFAULT_KEYWORDS] });
+    useEmailStore.setState({ tagCounts: {} });
+  });
+
+  it('uses the existing settings permissions for definition reads and writes', async () => {
+    expect(await gateError(plugin(), 'keywords.list', []))
+      .toMatch(/lacks permission "settings:read"/);
+    expect(await gateError(plugin(), 'keywords.add', [[]]))
+      .toMatch(/lacks permission "settings:write"/);
+
+    const reader = plugin({ permissions: ['settings:read'], grantedPermissions: ['settings:read'] });
+    expect(await dispatchApiCall(reader, 'keywords.list', []))
+      .toEqual(useSettingsStore.getState().emailKeywords);
+  });
+
+  it('only appends missing definitions and preserves existing user metadata', async () => {
+    useSettingsStore.setState({
+      emailKeywords: [{ id: 'work', label: 'My Work', color: 'purple', visibility: 'hide' }],
+    });
+    const writer = plugin({ permissions: ['settings:write'], grantedPermissions: ['settings:write'] });
+
+    const result = await dispatchApiCall(writer, 'keywords.add', [[
+      { id: 'WORK', label: 'Plugin Work', color: 'red' },
+      { id: 'gmail~shopping', label: 'Shopping', visibility: 'unread' },
+    ]]) as { added: Array<{ id: string }>; skipped: string[] };
+
+    expect(result.added.map((keyword) => keyword.id)).toEqual(['gmail~shopping']);
+    expect(result.skipped).toEqual(['WORK']);
+    expect(useSettingsStore.getState().emailKeywords).toEqual([
+      { id: 'work', label: 'My Work', color: 'purple', visibility: 'hide' },
+      expect.objectContaining({
+        id: 'gmail~shopping',
+        label: 'Shopping',
+        visibility: 'unread',
+        color: expect.any(String),
+      }),
+    ]);
+  });
+
+  it('rejects invalid definitions without partially updating settings', async () => {
+    useSettingsStore.setState({ emailKeywords: [...DEFAULT_KEYWORDS] });
+    const before = useSettingsStore.getState().emailKeywords;
+    const writer = plugin({ permissions: ['settings:write'], grantedPermissions: ['settings:write'] });
+
+    await expect(dispatchApiCall(writer, 'keywords.add', [[
+      { id: 'valid', label: 'Valid', color: 'blue' },
+      { id: 'invalid label', label: 'Invalid', color: 'blue' },
+    ]])).rejects.toThrow(/not a valid JMAP label id/);
+
+    expect(useSettingsStore.getState().emailKeywords).toEqual(before);
+  });
+
+  it('gates discovery and counts as email metadata', async () => {
+    for (const method of ['keywords.discover', 'keywords.getCounts', 'keywords.refreshCounts']) {
+      expect(await gateError(plugin(), method, [])).toMatch(/lacks permission "email:read"/);
+    }
+
+    useEmailStore.setState({ tagCounts: { shopping: { total: 9, unread: 2 } } });
+    const reader = plugin({ permissions: ['email:read'], grantedPermissions: ['email:read'] });
+    expect(await dispatchApiCall(reader, 'keywords.getCounts', [['shopping']]))
+      .toEqual({ shopping: { total: 9, unread: 2 } });
+  });
+});
diff --git a/lib/plugin-sandbox/host-api.ts b/lib/plugin-sandbox/host-api.ts
index 529d28255..f499aacaf 100644
--- a/lib/plugin-sandbox/host-api.ts
+++ b/lib/plugin-sandbox/host-api.ts
@@ -11,8 +11,18 @@ import { useIdentityStore } from '@/stores/identity-store';
 import { useEmailStore } from '@/stores/email-store';
 import { useFilterStore } from '@/stores/filter-store';
 import { useMessageListTabsStore } from '@/stores/message-list-tabs-store';
+import {
+  KEYWORD_PALETTE,
+  useSettingsStore,
+  type KeywordDefinition,
+  type KeywordVisibility,
+} from '@/stores/settings-store';
 import type { MessageListTabsConfig } from '../plugin-types';
 import { apiFetch } from '../browser-navigation';
+import { DEFAULT_KEYWORD_SCAN_LIMIT } from '../jmap/client';
+import { suggestKeywordColor } from '../keyword-discovery';
+import { MAX_KEYWORD_LENGTH } from '../keyword-nesting';
+import { KEYWORD_PREFIX } from '../thread-utils';
 import { awaitDialog, awaitPrompt, type PromptField } from './host-dialog';
 import { fileStorage } from '../plugin-storage';
 import { generateUUID } from '../utils';
@@ -109,6 +119,15 @@ const PERM_PER_METHOD: Record<string, Permission | null> = {
   // email keyword mutations
   'email.setKeyword': 'email:write',
   'email.removeKeyword': 'email:write',
+  // Native keyword definitions are a deliberately narrow settings API: a
+  // plugin can read definitions or append missing ones, but cannot overwrite
+  // or remove user-managed tags. Discovery/counts reveal mail metadata and
+  // therefore use email:read rather than a settings permission.
+  'keywords.list': 'settings:read',
+  'keywords.add': 'settings:write',
+  'keywords.discover': 'email:read',
+  'keywords.getCounts': 'email:read',
+  'keywords.refreshCounts': 'email:read',
   // message-list category tabs
   'tabs.set': 'ui:message-list-tabs',
   'tabs.clear': 'ui:message-list-tabs',
@@ -737,6 +756,164 @@ function requireClient() {
   return client;
 }
 
+// ─── Native keyword definitions ──────────────────────────────
+
+const MAX_PLUGIN_KEYWORD_DEFINITIONS = 500;
+const MAX_PLUGIN_KEYWORD_LABEL_LENGTH = 255;
+const VALID_VISIBILITIES = new Set<KeywordVisibility>(['show', 'hide', 'unread']);
+
+type PluginKeywordDefinitionInput = Omit<KeywordDefinition, 'color'> & { color?: string };
+
+function isPlainObject(value: unknown): value is Record<string, unknown> {
+  return typeof value === 'object' && value !== null && !Array.isArray(value);
+}
+
+/** RFC 8621 keyword syntax, applied to the complete `$label:<id>` value. */
+function isValidKeywordDefinitionId(id: string): boolean {
+  const keyword = KEYWORD_PREFIX + id;
+  if (id.length === 0 || keyword.length > MAX_KEYWORD_LENGTH) return false;
+  for (let i = 0; i < keyword.length; i++) {
+    const code = keyword.charCodeAt(i);
+    if (
+      code < 0x21 || code > 0x7e ||
+      code === 0x28 || code === 0x29 || code === 0x7b || code === 0x7d ||
+      code === 0x5d || code === 0x25 || code === 0x2a || code === 0x22 || code === 0x5c
+    ) {
+      return false;
+    }
+  }
+  return true;
+}
+
+function assertKeywordDefinition(value: unknown, index: number): PluginKeywordDefinitionInput {
+  if (!isPlainObject(value)) {
+    throw new Error(`keywords.add: definitions[${index}] must be an object`);
+  }
+
+  const id = value.id;
+  const label = value.label;
+  const color = value.color;
+  const visibility = value.visibility;
+
+  if (typeof id !== 'string' || !isValidKeywordDefinitionId(id)) {
+    throw new Error(`keywords.add: definitions[${index}].id is not a valid JMAP label id`);
+  }
+  if (
+    typeof label !== 'string' || label.trim().length === 0 ||
+    label.length > MAX_PLUGIN_KEYWORD_LABEL_LENGTH
+  ) {
+    throw new Error(
+      `keywords.add: definitions[${index}].label must be 1-${MAX_PLUGIN_KEYWORD_LABEL_LENGTH} characters`,
+    );
+  }
+  if (
+    color !== undefined &&
+    (typeof color !== 'string' || !Object.prototype.hasOwnProperty.call(KEYWORD_PALETTE, color))
+  ) {
+    throw new Error(`keywords.add: definitions[${index}].color is not in the keyword palette`);
+  }
+  if (visibility !== undefined && !VALID_VISIBILITIES.has(visibility as KeywordVisibility)) {
+    throw new Error(`keywords.add: definitions[${index}].visibility is invalid`);
+  }
+
+  return {
+    id,
+    label: label.trim(),
+    ...(color === undefined ? {} : { color }),
+    ...(visibility === undefined ? {} : { visibility: visibility as KeywordVisibility }),
+  };
+}
+
+function assertKeywordDefinitionArray(value: unknown): PluginKeywordDefinitionInput[] {
+  if (!Array.isArray(value)) throw new Error('keywords.add: definitions must be an array');
+  if (value.length > MAX_PLUGIN_KEYWORD_DEFINITIONS) {
+    throw new Error(`keywords.add: at most ${MAX_PLUGIN_KEYWORD_DEFINITIONS} definitions may be added at once`);
+  }
+  return value.map(assertKeywordDefinition);
+}
+
+function doKeywordsList(): KeywordDefinition[] {
+  return useSettingsStore.getState().emailKeywords.map((keyword) => ({ ...keyword }));
+}
+
+function doKeywordsAdd(value: unknown): { added: KeywordDefinition[]; skipped: string[] } {
+  const definitions = assertKeywordDefinitionArray(value);
+  const existing = useSettingsStore.getState().emailKeywords;
+  const known = new Set(existing.map((keyword) => keyword.id.toLowerCase()));
+  const takenColors = new Set(existing.map((keyword) => keyword.color));
+  const added: KeywordDefinition[] = [];
+  const skipped: string[] = [];
+
+  for (const definition of definitions) {
+    const foldedId = definition.id.toLowerCase();
+    if (known.has(foldedId)) {
+      skipped.push(definition.id);
+      continue;
+    }
+    known.add(foldedId);
+    const color = definition.color ?? suggestKeywordColor(definition.id, takenColors);
+    takenColors.add(color);
+    added.push({ ...definition, color });
+  }
+
+  if (added.length > 0) {
+    // One atomic append keeps concurrent plugin calls from partially
+    // overwriting the list and triggers the normal persist/settings-sync path.
+    useSettingsStore.setState((state) => ({
+      emailKeywords: [...state.emailKeywords, ...added],
+    }));
+  }
+
+  return { added: added.map((keyword) => ({ ...keyword })), skipped };
+}
+
+function assertKeywordIds(value: unknown): string[] | undefined {
+  if (value === undefined || value === null) return undefined;
+  if (!Array.isArray(value) || value.length > MAX_PLUGIN_KEYWORD_DEFINITIONS) {
+    throw new Error(`keywords.getCounts: ids must be an array of at most ${MAX_PLUGIN_KEYWORD_DEFINITIONS} strings`);
+  }
+  if (value.some((id) => typeof id !== 'string' || !isValidKeywordDefinitionId(id))) {
+    throw new Error('keywords.getCounts: ids contains an invalid label id');
+  }
+  return value as string[];
+}
+
+function doKeywordsGetCounts(value?: unknown): Record<string, { total: number; unread: number }> {
+  const ids = assertKeywordIds(value);
+  const counts = useEmailStore.getState().tagCounts;
+  if (!ids) {
+    return Object.fromEntries(
+      Object.entries(counts).map(([id, count]) => [id, { ...count }]),
+    );
+  }
+
+  const selected: Record<string, { total: number; unread: number }> = {};
+  for (const id of ids) {
+    const count = counts[id];
+    if (count) selected[id] = { ...count };
+  }
+  return selected;
+}
+
+async function doKeywordsDiscover(value?: unknown) {
+  if (value !== undefined && !isPlainObject(value)) {
+    throw new Error('keywords.discover: options must be an object');
+  }
+  const rawLimit = value?.limit;
+  if (
+    rawLimit !== undefined &&
+    (typeof rawLimit !== 'number' || !Number.isInteger(rawLimit) || rawLimit < 1 || rawLimit > DEFAULT_KEYWORD_SCAN_LIMIT)
+  ) {
+    throw new Error(`keywords.discover: limit must be an integer from 1 to ${DEFAULT_KEYWORD_SCAN_LIMIT}`);
+  }
+  return requireClient().discoverKeywords(rawLimit === undefined ? undefined : { limit: rawLimit });
+}
+
+async function doKeywordsRefreshCounts(): Promise<Record<string, { total: number; unread: number }>> {
+  await useEmailStore.getState().fetchTagCounts(requireClient());
+  return doKeywordsGetCounts();
+}
+
 // ─── Message-list category tabs ───────────────────────────────
 
 /**
@@ -999,6 +1176,12 @@ export async function dispatchApiCall(
       return undefined;
     }
 
+    case 'keywords.list': return doKeywordsList();
+    case 'keywords.add': return doKeywordsAdd(args[0]);
+    case 'keywords.discover': return doKeywordsDiscover(args[0]);
+    case 'keywords.getCounts': return doKeywordsGetCounts(args[0]);
+    case 'keywords.refreshCounts': return doKeywordsRefreshCounts();
+
     case 'tabs.set': {
       // validateTabsConfig (inside registerTabs) throws a developer-readable
       // error that surfaces as the api.tabs.set rejection in the sandbox.
@@ -1037,4 +1220,4 @@ export async function dispatchApiCall(
 
 // ─── Cleanup hook for unloading plugins ───────────────────────
 
-export { cancelForPlugin as cancelPluginDialogs } from './host-dialog';
\ No newline at end of file
+export { cancelForPlugin as cancelPluginDialogs } from './host-dialog';
diff --git a/lib/plugin-sandbox/protocol.ts b/lib/plugin-sandbox/protocol.ts
index 0ab19f001..ebc55f9a6 100644
--- a/lib/plugin-sandbox/protocol.ts
+++ b/lib/plugin-sandbox/protocol.ts
@@ -250,10 +250,12 @@ export const API_METHODS = [
   'ui.confirm', 'ui.alert', 'ui.prompt', 'ui.rerenderEmail', 'ui.rerenderFetchedEmails', 'ui.openExternalUrl', 'ui.downloadFile',
   // Email keyword mutations (JMAP Email/set keyword patches).
   'email.setKeyword', 'email.removeKeyword',
+  // Native tag definitions, discovery, and sidebar counts.
+  'keywords.list', 'keywords.add', 'keywords.discover', 'keywords.getCounts', 'keywords.refreshCounts',
   // Message-list category tabs (Gmail-style inbox tabs).
   'tabs.set', 'tabs.clear', 'tabs.getState', 'tabs.categorize', 'tabs.refreshCounts',
   // Sieve integration for delivery-time classification plugins.
   'sieve.isSupported', 'sieve.getActiveScript', 'sieve.validateScript', 'sieve.regenerate',
 ] as const;
 
-export type ApiMethod = (typeof API_METHODS)[number];
\ No newline at end of file
+export type ApiMethod = (typeof API_METHODS)[number];
diff --git a/lib/plugin-sandbox/runtime.tsx b/lib/plugin-sandbox/runtime.tsx
index 432c2d6d1..c1ddd9de3 100644
--- a/lib/plugin-sandbox/runtime.tsx
+++ b/lib/plugin-sandbox/runtime.tsx
@@ -165,6 +165,22 @@ function decodeCallbacks(value: unknown, depth = 0): unknown {
 
 type PluginManifest = BackgroundInit['manifest'];
 
+type PluginKeywordVisibility = 'show' | 'hide' | 'unread';
+
+interface PluginKeywordDefinition {
+  id: string;
+  label: string;
+  color: string;
+  visibility?: PluginKeywordVisibility;
+}
+
+type PluginKeywordDefinitionInput = Omit<PluginKeywordDefinition, 'color'> & { color?: string };
+
+interface PluginKeywordCounts {
+  total: number;
+  unread: number;
+}
+
 function buildPluginApi(manifest: PluginManifest) {
   return {
     plugin: {
@@ -289,6 +305,29 @@ function buildPluginApi(manifest: PluginManifest) {
       removeKeyword: (emailId: string, keyword: string, accountId?: string) =>
         callApi('email.removeKeyword', [emailId, keyword, accountId]) as Promise<void>,
     },
+    // Native sidebar tag definitions. Definition reads/writes use the existing
+    // settings permissions; server discovery and message counts use email:read.
+    // add() is intentionally append-only: it never overwrites or removes tags
+    // the user has already named, coloured, hidden, or reordered.
+    keywords: {
+      list: () => callApi('keywords.list', []) as Promise<PluginKeywordDefinition[]>,
+      add: (definitions: PluginKeywordDefinitionInput[]) =>
+        callApi('keywords.add', [definitions]) as Promise<{
+          added: PluginKeywordDefinition[];
+          skipped: string[];
+        }>,
+      discover: (options?: { limit?: number }) =>
+        callApi('keywords.discover', [options]) as Promise<{
+          keywords: Record<string, number>;
+          scanned: number;
+          total: number;
+          complete: boolean;
+        }>,
+      getCounts: (ids?: string[]) =>
+        callApi('keywords.getCounts', [ids]) as Promise<Record<string, PluginKeywordCounts>>,
+      refreshCounts: () =>
+        callApi('keywords.refreshCounts', []) as Promise<Record<string, PluginKeywordCounts>>,
+    },
     // Message-list category tabs (permission: ui:message-list-tabs; categorize
     // additionally needs email:write). The host renders the strip natively and
     // ANDs the active tab's JMAP search filter (`query`) or keyword into the
@@ -653,4 +692,4 @@ export function SandboxRuntime(): React.JSX.Element {
 
 // Suppress unused-variable warning when `mode` is only read for debugging.
 void mode;
-void slotName;
\ No newline at end of file
+void slotName;