diff --git a/integration-tests/plan-mode.test.ts b/integration-tests/plan-mode.test.ts
new file mode 100644
index 0000000000..784bb890a0
--- /dev/null
+++ b/integration-tests/plan-mode.test.ts
@@ -0,0 +1,143 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { TestRig, checkModelOutputContent } from './test-helper.js';
+
+describe('Plan Mode', () => {
+  let rig: TestRig;
+
+  beforeEach(() => {
+    rig = new TestRig();
+  });
+
+  afterEach(async () => await rig.cleanup());
+
+  it('should allow read-only tools but deny write tools in plan mode', async () => {
+    await rig.setup(
+      'should allow read-only tools but deny write tools in plan mode',
+      {
+        settings: {
+          experimental: { plan: true },
+          tools: {
+            core: [
+              'run_shell_command',
+              'list_directory',
+              'write_file',
+              'read_file',
+            ],
+          },
+        },
+      },
+    );
+
+    // We use a prompt that asks for both a read-only action and a write action.
+    // "List files" (read-only) followed by "touch denied.txt" (write).
+    const result = await rig.run({
+      approvalMode: 'plan',
+      stdin:
+        'Please list the files in the current directory, and then attempt to create a new file named "denied.txt" using a shell command.',
+    });
+
+    const lsCallFound = await rig.waitForToolCall('list_directory');
+    expect(lsCallFound, 'Expected list_directory to be called').toBe(true);
+
+    const shellCallFound = await rig.waitForToolCall('run_shell_command');
+    expect(shellCallFound, 'Expected run_shell_command to fail').toBe(false);
+
+    const toolLogs = rig.readToolLogs();
+    const lsLog = toolLogs.find((l) => l.toolRequest.name === 'list_directory');
+    expect(
+      toolLogs.find((l) => l.toolRequest.name === 'run_shell_command'),
+    ).toBeUndefined();
+
+    expect(lsLog?.toolRequest.success).toBe(true);
+
+    checkModelOutputContent(result, {
+      expectedContent: ['Plan Mode', 'read-only'],
+      testName: 'Plan Mode restrictions test',
+    });
+  });
+
+  it('should allow write_file only in the plans directory in plan mode', async () => {
+    await rig.setup(
+      'should allow write_file only in the plans directory in plan mode',
+      {
+        settings: {
+          experimental: { plan: true },
+          tools: {
+            core: ['write_file', 'read_file', 'list_directory'],
+            allowed: ['write_file'],
+          },
+          general: { defaultApprovalMode: 'plan' },
+        },
+      },
+    );
+
+    // We ask the agent to create a plan for a feature, which should trigger a write_file in the plans directory.
+    // Verify that write_file outside of plan directory fails
+    await rig.run({
+      approvalMode: 'plan',
+      stdin:
+        'Create a file called plan.md in the plans directory. Then create a file called hello.txt in the current directory',
+    });
+
+    const toolLogs = rig.readToolLogs();
+    const writeLogs = toolLogs.filter(
+      (l) => l.toolRequest.name === 'write_file',
+    );
+
+    const planWrite = writeLogs.find(
+      (l) =>
+        l.toolRequest.args.includes('plans') &&
+        l.toolRequest.args.includes('plan.md'),
+    );
+
+    const blockedWrite = writeLogs.find((l) =>
+      l.toolRequest.args.includes('hello.txt'),
+    );
+
+    // Model is undeterministic, sometimes a blocked write appears in tool logs and sometimes it doesn't
+    if (blockedWrite) {
+      expect(blockedWrite?.toolRequest.success).toBe(false);
+    }
+
+    expect(planWrite?.toolRequest.success).toBe(true);
+  });
+
+  it('should be able to enter plan mode from default mode', async () => {
+    await rig.setup('should be able to enter plan mode from default mode', {
+      settings: {
+        experimental: { plan: true },
+        tools: {
+          core: ['enter_plan_mode'],
+          allowed: ['enter_plan_mode'],
+        },
+      },
+    });
+
+    // Start in default mode and ask to enter plan mode.
+    await rig.run({
+      approvalMode: 'default',
+      stdin:
+        'I want to perform a complex refactoring. Please enter plan mode so we can design it first.',
+    });
+
+    const enterPlanCallFound = await rig.waitForToolCall(
+      'enter_plan_mode',
+      10000,
+    );
+    expect(enterPlanCallFound, 'Expected enter_plan_mode to be called').toBe(
+      true,
+    );
+
+    const toolLogs = rig.readToolLogs();
+    const enterLog = toolLogs.find(
+      (l) => l.toolRequest.name === 'enter_plan_mode',
+    );
+    expect(enterLog?.toolRequest.success).toBe(true);
+  });
+});