diff --git a/packages/brain/package.json b/packages/brain/package.json
index bb26908..4005827 100644
--- a/packages/brain/package.json
+++ b/packages/brain/package.json
@@ -22,7 +22,8 @@
   },
   "dependencies": {
     "@mosaicstack/db": "workspace:^",
-    "@mosaicstack/types": "workspace:*"
+    "@mosaicstack/types": "workspace:*",
+    "commander": "^13.0.0"
   },
   "devDependencies": {
     "typescript": "^5.8.0",
diff --git a/packages/brain/src/cli.spec.ts b/packages/brain/src/cli.spec.ts
new file mode 100644
index 0000000..a05238e
--- /dev/null
+++ b/packages/brain/src/cli.spec.ts
@@ -0,0 +1,95 @@
+import { describe, it, expect } from 'vitest';
+import { Command } from 'commander';
+import { registerBrainCommand } from './cli.js';
+
+/**
+ * Smoke test: verifies the command tree is correctly registered.
+ * No database connection is opened — we only inspect Commander metadata.
+ */
+describe('registerBrainCommand', () => {
+  function buildProgram(): Command {
+    const program = new Command('mosaic');
+    // Prevent Commander from calling process.exit on parse errors during tests.
+    program.exitOverride();
+    registerBrainCommand(program);
+    return program;
+  }
+
+  it('registers a top-level "brain" command', () => {
+    const program = buildProgram();
+    const brainCmd = program.commands.find((c) => c.name() === 'brain');
+    expect(brainCmd).toBeDefined();
+  });
+
+  it('registers "brain projects" with "list" and "create" subcommands', () => {
+    const program = buildProgram();
+    const brainCmd = program.commands.find((c) => c.name() === 'brain')!;
+    const projectsCmd = brainCmd.commands.find((c) => c.name() === 'projects');
+    expect(projectsCmd).toBeDefined();
+
+    const subNames = projectsCmd!.commands.map((c) => c.name());
+    expect(subNames).toContain('list');
+    expect(subNames).toContain('create');
+  });
+
+  it('registers "brain missions" with "list" subcommand', () => {
+    const program = buildProgram();
+    const brainCmd = program.commands.find((c) => c.name() === 'brain')!;
+    const missionsCmd = brainCmd.commands.find((c) => c.name() === 'missions');
+    expect(missionsCmd).toBeDefined();
+
+    const subNames = missionsCmd!.commands.map((c) => c.name());
+    expect(subNames).toContain('list');
+  });
+
+  it('registers "brain tasks" with "list" subcommand', () => {
+    const program = buildProgram();
+    const brainCmd = program.commands.find((c) => c.name() === 'brain')!;
+    const tasksCmd = brainCmd.commands.find((c) => c.name() === 'tasks');
+    expect(tasksCmd).toBeDefined();
+
+    const subNames = tasksCmd!.commands.map((c) => c.name());
+    expect(subNames).toContain('list');
+  });
+
+  it('registers "brain conversations" with "list" subcommand', () => {
+    const program = buildProgram();
+    const brainCmd = program.commands.find((c) => c.name() === 'brain')!;
+    const conversationsCmd = brainCmd.commands.find((c) => c.name() === 'conversations');
+    expect(conversationsCmd).toBeDefined();
+
+    const subNames = conversationsCmd!.commands.map((c) => c.name());
+    expect(subNames).toContain('list');
+  });
+
+  it('"brain projects list" accepts --db and --limit options', () => {
+    const program = buildProgram();
+    const brainCmd = program.commands.find((c) => c.name() === 'brain')!;
+    const projectsCmd = brainCmd.commands.find((c) => c.name() === 'projects')!;
+    const listCmd = projectsCmd.commands.find((c) => c.name() === 'list')!;
+
+    const optionNames = listCmd.options.map((o) => o.long);
+    expect(optionNames).toContain('--db');
+    expect(optionNames).toContain('--limit');
+  });
+
+  it('"brain missions list" accepts --project option', () => {
+    const program = buildProgram();
+    const brainCmd = program.commands.find((c) => c.name() === 'brain')!;
+    const missionsCmd = brainCmd.commands.find((c) => c.name() === 'missions')!;
+    const listCmd = missionsCmd.commands.find((c) => c.name() === 'list')!;
+
+    const optionNames = listCmd.options.map((o) => o.long);
+    expect(optionNames).toContain('--project');
+  });
+
+  it('"brain tasks list" accepts --project option', () => {
+    const program = buildProgram();
+    const brainCmd = program.commands.find((c) => c.name() === 'brain')!;
+    const tasksCmd = brainCmd.commands.find((c) => c.name() === 'tasks')!;
+    const listCmd = tasksCmd.commands.find((c) => c.name() === 'list')!;
+
+    const optionNames = listCmd.options.map((o) => o.long);
+    expect(optionNames).toContain('--project');
+  });
+});
diff --git a/packages/brain/src/cli.ts b/packages/brain/src/cli.ts
new file mode 100644
index 0000000..908e371
--- /dev/null
+++ b/packages/brain/src/cli.ts
@@ -0,0 +1,142 @@
+import type { Command } from 'commander';
+import { createDb, type DbHandle } from '@mosaicstack/db';
+import { createBrain } from './brain.js';
+
+/**
+ * Build and attach the `brain` subcommand tree onto an existing Commander program.
+ * Uses the caller's Command instance to avoid cross-package Commander version mismatches.
+ */
+export function registerBrainCommand(parent: Command): void {
+  const brain = parent.command('brain').description('Inspect and manage brain data stores');
+
+  // ─── shared DB option helper ─────────────────────────────────────────────
+
+  function addDbOption(cmd: Command): Command {
+    return cmd.option(
+      '--db <connection-string>',
+      'PostgreSQL connection string (overrides MOSAIC_DB_URL)',
+    );
+  }
+
+  function resolveDb(opts: { db?: string }): ReturnType<typeof createBrain> {
+    const connectionString = opts.db ?? process.env['MOSAIC_DB_URL'];
+    if (!connectionString) {
+      console.error('No DB connection string provided. Pass --db <url> or set MOSAIC_DB_URL.');
+      process.exit(1);
+    }
+    const handle: DbHandle = createDb(connectionString);
+    return createBrain(handle.db);
+  }
+
+  // ─── projects ────────────────────────────────────────────────────────────
+
+  const projects = brain.command('projects').description('Manage projects');
+
+  addDbOption(
+    projects
+      .command('list')
+      .description('List all projects')
+      .option('--limit <n>', 'Maximum number of results', '50'),
+  ).action(async (opts: { db?: string; limit: string }) => {
+    const b = resolveDb(opts);
+    const limit = parseInt(opts.limit, 10);
+    const rows = await b.projects.findAll();
+    const sliced = rows.slice(0, limit);
+    if (sliced.length === 0) {
+      console.log('No projects found.');
+      return;
+    }
+    for (const p of sliced) {
+      console.log(`${p.id}  ${p.name}`);
+    }
+  });
+
+  addDbOption(
+    projects
+      .command('create <name>')
+      .description('Create a new project')
+      .requiredOption('--owner-id <id>', 'Owner user ID'),
+  ).action(async (name: string, opts: { db?: string; ownerId: string }) => {
+    const b = resolveDb(opts);
+    const created = await b.projects.create({
+      name,
+      ownerId: opts.ownerId,
+      ownerType: 'user',
+    });
+    console.log(`Created project: ${created.id}  ${created.name}`);
+  });
+
+  // ─── missions ────────────────────────────────────────────────────────────
+
+  const missions = brain.command('missions').description('Manage missions');
+
+  addDbOption(
+    missions
+      .command('list')
+      .description('List all missions')
+      .option('--limit <n>', 'Maximum number of results', '50')
+      .option('--project <id>', 'Filter by project ID'),
+  ).action(async (opts: { db?: string; limit: string; project?: string }) => {
+    const b = resolveDb(opts);
+    const limit = parseInt(opts.limit, 10);
+    const rows = opts.project
+      ? await b.missions.findByProject(opts.project)
+      : await b.missions.findAll();
+    const sliced = rows.slice(0, limit);
+    if (sliced.length === 0) {
+      console.log('No missions found.');
+      return;
+    }
+    for (const m of sliced) {
+      console.log(`${m.id}  ${m.name}`);
+    }
+  });
+
+  // ─── tasks ────────────────────────────────────────────────────────────────
+
+  const tasks = brain.command('tasks').description('Manage generic tasks');
+
+  addDbOption(
+    tasks
+      .command('list')
+      .description('List all tasks')
+      .option('--limit <n>', 'Maximum number of results', '50')
+      .option('--project <id>', 'Filter by project ID'),
+  ).action(async (opts: { db?: string; limit: string; project?: string }) => {
+    const b = resolveDb(opts);
+    const limit = parseInt(opts.limit, 10);
+    const rows = opts.project ? await b.tasks.findByProject(opts.project) : await b.tasks.findAll();
+    const sliced = rows.slice(0, limit);
+    if (sliced.length === 0) {
+      console.log('No tasks found.');
+      return;
+    }
+    for (const t of sliced) {
+      console.log(`${t.id}  ${t.title}  [${t.status}]`);
+    }
+  });
+
+  // ─── conversations ────────────────────────────────────────────────────────
+
+  const conversations = brain.command('conversations').description('Manage conversations');
+
+  addDbOption(
+    conversations
+      .command('list')
+      .description('List conversations for a user')
+      .option('--limit <n>', 'Maximum number of results', '50')
+      .requiredOption('--user-id <id>', 'User ID to scope the query'),
+  ).action(async (opts: { db?: string; limit: string; userId: string }) => {
+    const b = resolveDb(opts);
+    const limit = parseInt(opts.limit, 10);
+    const rows = await b.conversations.findAll(opts.userId);
+    const sliced = rows.slice(0, limit);
+    if (sliced.length === 0) {
+      console.log('No conversations found.');
+      return;
+    }
+    for (const c of sliced) {
+      console.log(`${c.id}  ${c.title ?? '(untitled)'}`);
+    }
+  });
+}
diff --git a/packages/brain/src/index.ts b/packages/brain/src/index.ts
index 8bf5516..a024854 100644
--- a/packages/brain/src/index.ts
+++ b/packages/brain/src/index.ts
@@ -1,4 +1,5 @@
 export { createBrain, type Brain } from './brain.js';
+export { registerBrainCommand } from './cli.js';
 export {
   createProjectsRepo,
   type ProjectsRepo,
diff --git a/packages/mosaic/package.json b/packages/mosaic/package.json
index 466ee96..f5a3def 100644
--- a/packages/mosaic/package.json
+++ b/packages/mosaic/package.json
@@ -27,6 +27,7 @@
     "test": "vitest run --passWithNoTests"
   },
   "dependencies": {
+    "@mosaicstack/brain": "workspace:*",
     "@mosaicstack/config": "workspace:*",
     "@mosaicstack/forge": "workspace:*",
     "@mosaicstack/macp": "workspace:*",
diff --git a/packages/mosaic/src/cli.ts b/packages/mosaic/src/cli.ts
index 03444d9..4b7e0d7 100644
--- a/packages/mosaic/src/cli.ts
+++ b/packages/mosaic/src/cli.ts
@@ -2,6 +2,7 @@
 
 import { createRequire } from 'module';
 import { Command } from 'commander';
+import { registerBrainCommand } from '@mosaicstack/brain';
 import { registerQualityRails } from '@mosaicstack/quality-rails';
 import { registerAgentCommand } from './commands/agent.js';
 import { registerMissionCommand } from './commands/mission.js';
@@ -333,6 +334,10 @@ registerAgentCommand(program);
 
 registerMissionCommand(program);
 
+// ─── brain ──────────────────────────────────────────────────────────────
+
+registerBrainCommand(program);
+
 // ─── quality-rails ──────────────────────────────────────────────────────
 
 registerQualityRails(program);
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index df1291d..5fbbfb8 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -294,6 +294,9 @@ importers:
       '@mosaicstack/types':
         specifier: workspace:*
         version: link:../types
+      commander:
+        specifier: ^13.0.0
+        version: 13.1.0
     devDependencies:
       typescript:
         specifier: ^5.8.0
@@ -454,6 +457,9 @@ importers:
       '@clack/prompts':
         specifier: ^0.9.1
         version: 0.9.1
+      '@mosaicstack/brain':
+        specifier: workspace:*
+        version: link:../brain
       '@mosaicstack/config':
         specifier: workspace:*
         version: link:../config