diff --git a/tests/daemon/utils.test.ts b/tests/daemon/utils.test.ts
index 41e13ab4c..b345c817d 100644
--- a/tests/daemon/utils.test.ts
+++ b/tests/daemon/utils.test.ts
@@ -5,12 +5,30 @@
  */
 
 import assert from 'node:assert';
-import {describe, it} from 'node:test';
+import {spawn} from 'node:child_process';
+import {once} from 'node:events';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import process from 'node:process';
+import {afterEach, beforeEach, describe, it} from 'node:test';
 
 import type {ParsedArguments} from '../../src/bin/chrome-devtools-mcp-cli-options.js';
-import {serializeArgs, assertValidSessionId} from '../../src/daemon/utils.js';
+import {
+  serializeArgs,
+  assertValidSessionId,
+  getSocketPath,
+  getRuntimeHome,
+  getPidFilePath,
+  getDaemonPid,
+  isDaemonRunning,
+  IS_WINDOWS,
+} from '../../src/daemon/utils.js';
 import type {YargsOptions} from '../../src/third_party/index.js';
 
+const APP_NAME = 'chrome-devtools-mcp';
+const SESSION_ID = 'aabbccdd-1122-3344-5566-77889900aabb';
+
 describe('assertValidSessionId', () => {
   it('should not throw for empty sessionId', () => {
     assert.doesNotThrow(() => assertValidSessionId(''));
@@ -121,3 +139,226 @@ describe('serializeArgs', () => {
     ]);
   });
 });
+
+describe('getRuntimeHome', () => {
+  let savedXdgRuntimeDir: string | undefined;
+
+  beforeEach(() => {
+    savedXdgRuntimeDir = process.env['XDG_RUNTIME_DIR'];
+  });
+
+  afterEach(() => {
+    if (savedXdgRuntimeDir === undefined) {
+      delete process.env['XDG_RUNTIME_DIR'];
+    } else {
+      process.env['XDG_RUNTIME_DIR'] = savedXdgRuntimeDir;
+    }
+  });
+
+  it('uses XDG_RUNTIME_DIR when set', () => {
+    const xdgDir = path.join(os.tmpdir(), 'xdg-test');
+    process.env['XDG_RUNTIME_DIR'] = xdgDir;
+    assert.strictEqual(getRuntimeHome(''), path.join(xdgDir, APP_NAME));
+    assert.strictEqual(
+      getRuntimeHome(SESSION_ID),
+      path.join(xdgDir, `${APP_NAME}-${SESSION_ID}`),
+    );
+  });
+
+  it(
+    'falls back to /tmp with the uid when XDG_RUNTIME_DIR is unset',
+    {skip: IS_WINDOWS},
+    () => {
+      delete process.env['XDG_RUNTIME_DIR'];
+      const uid = os.userInfo().uid;
+      assert.strictEqual(getRuntimeHome(''), `/tmp/${APP_NAME}-${uid}`);
+      assert.strictEqual(
+        getRuntimeHome(SESSION_ID),
+        `/tmp/${APP_NAME}-${SESSION_ID}-${uid}`,
+      );
+    },
+  );
+
+  it(
+    'falls back to os.tmpdir() on Windows when XDG_RUNTIME_DIR is unset',
+    {skip: !IS_WINDOWS},
+    () => {
+      delete process.env['XDG_RUNTIME_DIR'];
+      assert.strictEqual(getRuntimeHome(''), path.join(os.tmpdir(), APP_NAME));
+    },
+  );
+
+  it('throws for invalid session ids', () => {
+    assert.throws(() => getRuntimeHome('../escape'), /Invalid sessionId/);
+  });
+});
+
+describe('getSocketPath', () => {
+  let savedXdgRuntimeDir: string | undefined;
+
+  beforeEach(() => {
+    savedXdgRuntimeDir = process.env['XDG_RUNTIME_DIR'];
+  });
+
+  afterEach(() => {
+    if (savedXdgRuntimeDir === undefined) {
+      delete process.env['XDG_RUNTIME_DIR'];
+    } else {
+      process.env['XDG_RUNTIME_DIR'] = savedXdgRuntimeDir;
+    }
+  });
+
+  it('uses XDG_RUNTIME_DIR when set', {skip: IS_WINDOWS}, () => {
+    const xdgDir = path.join(os.tmpdir(), 'xdg-test');
+    process.env['XDG_RUNTIME_DIR'] = xdgDir;
+    assert.strictEqual(
+      getSocketPath(''),
+      path.join(xdgDir, APP_NAME, 'server.sock'),
+    );
+    assert.strictEqual(
+      getSocketPath(SESSION_ID),
+      path.join(xdgDir, `${APP_NAME}-${SESSION_ID}`, 'server.sock'),
+    );
+  });
+
+  it(
+    'falls back to a /tmp socket with the uid when XDG_RUNTIME_DIR is unset',
+    {skip: IS_WINDOWS},
+    () => {
+      delete process.env['XDG_RUNTIME_DIR'];
+      const uid = os.userInfo().uid;
+      assert.strictEqual(getSocketPath(''), `/tmp/${APP_NAME}-${uid}.sock`);
+      assert.strictEqual(
+        getSocketPath(SESSION_ID),
+        `/tmp/${APP_NAME}-${SESSION_ID}-${uid}.sock`,
+      );
+    },
+  );
+
+  it(
+    'stays under the POSIX socket path length limit for UUID session ids',
+    {skip: IS_WINDOWS},
+    () => {
+      delete process.env['XDG_RUNTIME_DIR'];
+      // macOS limits sun_path to 104 characters.
+      assert.ok(getSocketPath(SESSION_ID).length < 104);
+    },
+  );
+
+  it('uses a named pipe on Windows', {skip: !IS_WINDOWS}, () => {
+    const socketPath = getSocketPath(SESSION_ID);
+    assert.ok(socketPath.startsWith('\\\\.\\pipe\\'));
+    assert.ok(socketPath.includes(SESSION_ID));
+    // The username is appended to prevent cross-user pipe squatting.
+    assert.ok(socketPath.includes(os.userInfo().username));
+  });
+
+  it('throws for invalid session ids', () => {
+    assert.throws(() => getSocketPath('../escape'), /Invalid sessionId/);
+  });
+});
+
+describe('getPidFilePath', () => {
+  it('is daemon.pid inside the runtime home', () => {
+    assert.strictEqual(
+      getPidFilePath(SESSION_ID),
+      path.join(getRuntimeHome(SESSION_ID), 'daemon.pid'),
+    );
+    assert.strictEqual(path.basename(getPidFilePath('')), 'daemon.pid');
+  });
+
+  it('throws for invalid session ids', () => {
+    assert.throws(() => getPidFilePath('../escape'), /Invalid sessionId/);
+  });
+});
+
+describe('daemon pid handling', () => {
+  let savedXdgRuntimeDir: string | undefined;
+  let tempDir: string;
+
+  beforeEach(() => {
+    savedXdgRuntimeDir = process.env['XDG_RUNTIME_DIR'];
+    // Point XDG_RUNTIME_DIR at a temp dir so the pid file paths used by
+    // getDaemonPid/isDaemonRunning are isolated from any real daemon.
+    tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'cdm-daemon-utils-test-'));
+    process.env['XDG_RUNTIME_DIR'] = tempDir;
+  });
+
+  afterEach(() => {
+    if (savedXdgRuntimeDir === undefined) {
+      delete process.env['XDG_RUNTIME_DIR'];
+    } else {
+      process.env['XDG_RUNTIME_DIR'] = savedXdgRuntimeDir;
+    }
+    fs.rmSync(tempDir, {recursive: true, force: true});
+  });
+
+  function writePidFile(sessionId: string, contents: string): void {
+    const pidFile = getPidFilePath(sessionId);
+    fs.mkdirSync(path.dirname(pidFile), {recursive: true});
+    fs.writeFileSync(pidFile, contents);
+  }
+
+  describe('getDaemonPid', () => {
+    it('returns null when no pid file exists', () => {
+      assert.strictEqual(getDaemonPid(SESSION_ID), null);
+    });
+
+    it('reads the pid from the pid file, ignoring whitespace', () => {
+      writePidFile(SESSION_ID, '12345\n');
+      assert.strictEqual(getDaemonPid(SESSION_ID), 12345);
+    });
+
+    it('is scoped per session id', () => {
+      writePidFile(SESSION_ID, '12345\n');
+      assert.strictEqual(getDaemonPid('00000000-0000'), null);
+    });
+
+    it('returns null for empty or non-numeric pid files', () => {
+      writePidFile(SESSION_ID, '');
+      assert.strictEqual(getDaemonPid(SESSION_ID), null);
+      writePidFile(SESSION_ID, 'not-a-pid');
+      assert.strictEqual(getDaemonPid(SESSION_ID), null);
+    });
+
+    it('parses the leading integer of malformed contents', () => {
+      // Documents current parseInt-based behavior.
+      writePidFile(SESSION_ID, '123abc');
+      assert.strictEqual(getDaemonPid(SESSION_ID), 123);
+    });
+  });
+
+  describe('isDaemonRunning', () => {
+    it('returns false when no pid file exists', () => {
+      assert.strictEqual(isDaemonRunning(SESSION_ID), false);
+    });
+
+    it('returns true when the pid file points to a live process', () => {
+      writePidFile(SESSION_ID, `${process.pid}\n`);
+      assert.strictEqual(isDaemonRunning(SESSION_ID), true);
+    });
+
+    it('returns false when the pid file points to a dead process', async () => {
+      const child = spawn(process.execPath, ['--version'], {stdio: 'ignore'});
+      await once(child, 'exit');
+      assert.ok(child.pid);
+      // In theory the OS could reuse the pid between the child exiting and
+      // this check, but pid reuse within milliseconds is practically
+      // impossible on all supported platforms.
+      writePidFile(SESSION_ID, `${child.pid}\n`);
+      assert.strictEqual(isDaemonRunning(SESSION_ID), false);
+    });
+
+    it('returns false when the pid file contains 0', () => {
+      // Important: signaling pid 0 would target the whole process group, so
+      // isDaemonRunning must not treat it as a live daemon.
+      writePidFile(SESSION_ID, '0');
+      assert.strictEqual(isDaemonRunning(SESSION_ID), false);
+    });
+
+    it('returns false for non-numeric pid files', () => {
+      writePidFile(SESSION_ID, 'garbage');
+      assert.strictEqual(isDaemonRunning(SESSION_ID), false);
+    });
+  });
+});