diff --git a/packages/rules/__tests__/init/detect-tools.test.js b/packages/rules/__tests__/init/detect-tools.test.js
new file mode 100644
index 00000000..21ed1ef1
--- /dev/null
+++ b/packages/rules/__tests__/init/detect-tools.test.js
@@ -0,0 +1,148 @@
+const { describe, it, beforeEach, afterEach } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const os = require('node:os');
+
+const { detectTools, AI_TOOLS } = require('../../lib/init/detect-tools');
+
+describe('detectTools', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'cb-test-tools-'));
+  });
+
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it('returns all 6 tools for empty directory', () => {
+    const results = detectTools(tmpDir);
+    assert.equal(results.length, 6);
+    for (const tool of results) {
+      assert.equal(tool.exists, false);
+      assert.equal(tool.hasRules, false);
+      assert.deepEqual(tool.configFiles, []);
+    }
+  });
+
+  it('detects Cursor from .cursor/ directory', () => {
+    fs.mkdirSync(path.join(tmpDir, '.cursor'));
+    fs.writeFileSync(path.join(tmpDir, '.cursor', 'settings.json'), '{}');
+
+    const results = detectTools(tmpDir);
+    const cursor = results.find(t => t.name === 'Cursor');
+    assert.equal(cursor.exists, true);
+    assert.ok(cursor.configFiles.includes('settings.json'));
+    assert.equal(cursor.indicator, 'AI rules config');
+  });
+
+  it('detects Cursor from .cursorrules file', () => {
+    fs.writeFileSync(path.join(tmpDir, '.cursorrules'), 'rules content');
+
+    const results = detectTools(tmpDir);
+    const cursor = results.find(t => t.name === 'Cursor');
+    assert.equal(cursor.exists, true);
+    assert.equal(cursor.hasRules, true);
+    assert.ok(cursor.configFiles.includes('.cursorrules'));
+  });
+
+  it('detects Claude Code from .claude/ directory', () => {
+    fs.mkdirSync(path.join(tmpDir, '.claude'));
+    fs.writeFileSync(path.join(tmpDir, '.claude', 'settings.json'), '{}');
+
+    const results = detectTools(tmpDir);
+    const claude = results.find(t => t.name === 'Claude Code');
+    assert.equal(claude.exists, true);
+    assert.equal(claude.hasRules, false);
+    assert.ok(claude.configFiles.includes('settings.json'));
+  });
+
+  it('detects Claude Code hasRules when rules/ exists', () => {
+    fs.mkdirSync(path.join(tmpDir, '.claude', 'rules'), { recursive: true });
+
+    const results = detectTools(tmpDir);
+    const claude = results.find(t => t.name === 'Claude Code');
+    assert.equal(claude.exists, true);
+    assert.equal(claude.hasRules, true);
+  });
+
+  it('detects Codex from .codex/ directory', () => {
+    fs.mkdirSync(path.join(tmpDir, '.codex'));
+    fs.writeFileSync(path.join(tmpDir, '.codex', 'instructions.md'), '# Instructions');
+
+    const results = detectTools(tmpDir);
+    const codex = results.find(t => t.name === 'Codex');
+    assert.equal(codex.exists, true);
+    assert.equal(codex.hasRules, true);
+  });
+
+  it('detects Antigravity from .antigravity/ directory', () => {
+    fs.mkdirSync(path.join(tmpDir, '.antigravity'));
+    fs.writeFileSync(path.join(tmpDir, '.antigravity', 'config.json'), '{}');
+
+    const results = detectTools(tmpDir);
+    const ag = results.find(t => t.name === 'Antigravity');
+    assert.equal(ag.exists, true);
+    assert.ok(ag.configFiles.includes('config.json'));
+  });
+
+  it('detects Amazon Q from .q/ directory', () => {
+    fs.mkdirSync(path.join(tmpDir, '.q'));
+
+    const results = detectTools(tmpDir);
+    const q = results.find(t => t.name === 'Amazon Q');
+    assert.equal(q.exists, true);
+    assert.equal(q.hasRules, false);
+  });
+
+  it('detects Kiro from .kiro/ directory', () => {
+    fs.mkdirSync(path.join(tmpDir, '.kiro'));
+    fs.writeFileSync(path.join(tmpDir, '.kiro', 'config.json'), '{}');
+
+    const results = detectTools(tmpDir);
+    const kiro = results.find(t => t.name === 'Kiro');
+    assert.equal(kiro.exists, true);
+    assert.ok(kiro.configFiles.includes('config.json'));
+  });
+
+  it('detects multiple tools simultaneously', () => {
+    fs.mkdirSync(path.join(tmpDir, '.cursor'));
+    fs.mkdirSync(path.join(tmpDir, '.claude'));
+    fs.mkdirSync(path.join(tmpDir, '.codex'));
+
+    const results = detectTools(tmpDir);
+    const detected = results.filter(t => t.exists);
+    assert.equal(detected.length, 3);
+
+    const names = detected.map(t => t.name);
+    assert.ok(names.includes('Cursor'));
+    assert.ok(names.includes('Claude Code'));
+    assert.ok(names.includes('Codex'));
+  });
+
+  it('returns correct structure for each tool', () => {
+    const results = detectTools(tmpDir);
+    for (const tool of results) {
+      assert.ok(typeof tool.name === 'string');
+      assert.ok(typeof tool.configDir === 'string');
+      assert.ok(typeof tool.exists === 'boolean');
+      assert.ok(typeof tool.hasRules === 'boolean');
+      assert.ok(Array.isArray(tool.configFiles));
+      assert.ok(typeof tool.indicator === 'string');
+    }
+  });
+
+  it('lists config files in detected tool directory', () => {
+    fs.mkdirSync(path.join(tmpDir, '.claude'));
+    fs.writeFileSync(path.join(tmpDir, '.claude', 'settings.json'), '{}');
+    fs.writeFileSync(path.join(tmpDir, '.claude', 'CLAUDE.md'), '# Claude');
+
+    const results = detectTools(tmpDir);
+    const claude = results.find(t => t.name === 'Claude Code');
+    assert.ok(claude.configFiles.includes('settings.json'));
+    assert.ok(claude.configFiles.includes('CLAUDE.md'));
+    assert.equal(claude.configFiles.length, 2);
+  });
+});
diff --git a/packages/rules/lib/init/detect-tools.js b/packages/rules/lib/init/detect-tools.js
new file mode 100644
index 00000000..fbf47adb
--- /dev/null
+++ b/packages/rules/lib/init/detect-tools.js
@@ -0,0 +1,116 @@
+'use strict';
+
+const fs = require('node:fs');
+const path = require('node:path');
+
+const AI_TOOLS = [
+  {
+    name: 'Cursor',
+    configDir: '.cursor',
+    indicator: 'AI rules config',
+    rulesPatterns: ['rules/', 'rules.md', 'rules.json'],
+    altPaths: ['.cursorrules'],
+  },
+  {
+    name: 'Claude Code',
+    configDir: '.claude',
+    indicator: 'Plugin/settings',
+    rulesPatterns: ['rules/'],
+    altPaths: [],
+  },
+  {
+    name: 'Codex',
+    configDir: '.codex',
+    indicator: 'Codex config',
+    rulesPatterns: ['instructions.md'],
+    altPaths: [],
+  },
+  {
+    name: 'Antigravity',
+    configDir: '.antigravity',
+    indicator: 'Gemini config',
+    rulesPatterns: ['rules/', 'config.json'],
+    altPaths: [],
+  },
+  {
+    name: 'Amazon Q',
+    configDir: '.q',
+    indicator: 'Q config',
+    rulesPatterns: ['rules/', 'settings.json'],
+    altPaths: [],
+  },
+  {
+    name: 'Kiro',
+    configDir: '.kiro',
+    indicator: 'Kiro config',
+    rulesPatterns: ['rules/', 'config.json'],
+    altPaths: [],
+  },
+];
+
+/**
+ * Detect installed AI coding tools in the given directory.
+ * @param {string} cwd - Directory to scan
+ * @returns {Array<{ name: string, configDir: string, exists: boolean, hasRules: boolean, configFiles: string[], indicator: string }>}
+ */
+function detectTools(cwd) {
+  return AI_TOOLS.map(tool => {
+    const dirPath = path.join(cwd, tool.configDir);
+    const dirExists = fs.existsSync(dirPath);
+
+    // Check alternative paths (e.g. .cursorrules)
+    const altExists = tool.altPaths.some(alt => fs.existsSync(path.join(cwd, alt)));
+    const exists = dirExists || altExists;
+
+    let configFiles = [];
+    let hasRules = false;
+
+    if (dirExists) {
+      configFiles = listConfigFiles(dirPath);
+      hasRules = tool.rulesPatterns.some(pattern => {
+        const fullPath = path.join(dirPath, pattern);
+        return fs.existsSync(fullPath);
+      });
+    }
+
+    if (altExists) {
+      for (const alt of tool.altPaths) {
+        if (fs.existsSync(path.join(cwd, alt))) {
+          configFiles.push(alt);
+          hasRules = true;
+        }
+      }
+    }
+
+    return {
+      name: tool.name,
+      configDir: tool.configDir,
+      exists,
+      hasRules,
+      configFiles,
+      indicator: tool.indicator,
+    };
+  });
+}
+
+/**
+ * List files in a config directory (non-recursive, top-level only).
+ * @param {string} dirPath - Directory to list
+ * @returns {string[]}
+ */
+function listConfigFiles(dirPath) {
+  try {
+    return fs.readdirSync(dirPath).filter(entry => {
+      const fullPath = path.join(dirPath, entry);
+      try {
+        return fs.statSync(fullPath).isFile();
+      } catch {
+        return false;
+      }
+    });
+  } catch {
+    return [];
+  }
+}
+
+module.exports = { detectTools, AI_TOOLS };