feat: Add offline network emulation support to emulate_network command (#326)

#320
Issue:
It would be very useful to have the ability to simulate offline network
conditions directly through the MCP emulate_network command, similar to
how it's possible in DevTools.
Currently, the command doesn’t support an Offline state, which limits
testing for PWA and offline-first web applications. Adding this option
would make it easier to automate and validate offline behavior through
MCP scripts or tools that rely on this API.

Solution
- Add 'Offline' option to throttlingOptions for simulating offline
network conditions
- Update emulate_network tool to handle offline mode with proper network
conditions
- Update documentation to include offline option and usage instructions
- Add test coverage for offline network emulation functionality
- Enable testing of PWA and offline-first web applications through MCP

Author: iamitesh

docs/tool-reference.md

@@ -200,11 +200,11 @@
 
 ### `emulate_network`
 
-**Description:** Emulates network conditions such as throttling on the selected page.
+**Description:** Emulates network conditions such as throttling or offline mode on the selected page.
 
 **Parameters:**
 
-- **throttlingOption** (enum: "No emulation", "Slow 3G", "Fast 3G", "Slow 4G", "Fast 4G") **(required)**: The network throttling option to emulate. Available throttling options are: No emulation, Slow 3G, Fast 3G, Slow 4G, Fast 4G. Set to "No emulation" to disable.
+- **throttlingOption** (enum: "No emulation", "Offline", "Slow 3G", "Fast 3G", "Slow 4G", "Fast 4G") **(required)**: The network throttling option to emulate. Available throttling options are: No emulation, Offline, Slow 3G, Fast 3G, Slow 4G, Fast 4G. Set to "No emulation" to disable. Set to "Offline" to simulate offline network conditions.
 
 ---
 

package-lock.json

@@ -40,8 +40,9 @@
     "@modelcontextprotocol/sdk": "1.19.1",
     "core-js": "3.45.1",
     "debug": "4.4.3",
-    "puppeteer-core": "24.23.0",
-    "yargs": "18.0.0"
+    "puppeteer-core": "^24.23.0",
+    "yargs": "18.0.0",
+    "zod": "^3.25.76"
   },
   "devDependencies": {
     "@eslint/js": "^9.35.0",

package.json

@@ -12,12 +12,13 @@ import {defineTool} from './ToolDefinition.js';
 
 const throttlingOptions: [string, ...string[]] = [
   'No emulation',
+  'Offline',
   ...Object.keys(PredefinedNetworkConditions),
 ];
 
 export const emulateNetwork = defineTool({
   name: 'emulate_network',
-  description: `Emulates network conditions such as throttling on the selected page.`,
+  description: `Emulates network conditions such as throttling or offline mode on the selected page.`,
   annotations: {
     category: ToolCategories.EMULATION,
     readOnlyHint: false,
@@ -26,7 +27,7 @@ export const emulateNetwork = defineTool({
     throttlingOption: z
       .enum(throttlingOptions)
       .describe(
-        `The network throttling option to emulate. Available throttling options are: ${throttlingOptions.join(', ')}. Set to "No emulation" to disable.`,
+        `The network throttling option to emulate. Available throttling options are: ${throttlingOptions.join(', ')}. Set to "No emulation" to disable. Set to "Offline" to simulate offline network conditions.`,
       ),
   },
   handler: async (request, _response, context) => {
@@ -39,6 +40,17 @@ export const emulateNetwork = defineTool({
       return;
     }
 
+    if (conditions === 'Offline') {
+      await page.emulateNetworkConditions({
+        offline: true,
+        download: 0,
+        upload: 0,
+        latency: 0,
+      });
+      context.setNetworkConditions('Offline');
+      return;
+    }
+
     if (conditions in PredefinedNetworkConditions) {
       const networkCondition =
         PredefinedNetworkConditions[

src/tools/emulation.ts

@@ -11,6 +11,21 @@ import {withBrowser} from '../utils.js';
 
 describe('emulation', () => {
   describe('network', () => {
+    it('emulates offline network conditions', async () => {
+      await withBrowser(async (response, context) => {
+        await emulateNetwork.handler(
+          {
+            params: {
+              throttlingOption: 'Offline',
+            },
+          },
+          response,
+          context,
+        );
+
+        assert.strictEqual(context.getNetworkConditions(), 'Offline');
+      });
+    });
     it('emulates network throttling when the throttling option is valid ', async () => {
       await withBrowser(async (response, context) => {
         await emulateNetwork.handler(