HAR Extraction & Mock Generation

Extract JSON mocks from HAR files and integrate with MSW for testing and Storybook.

Workflow

HAR File → har-to-mocks → JSON Mocks → mocks-to-msw → MSW Handlers → Storybook/Tests

Quick Start

1. Extract mocks from HAR file

npx har-to-mocks recording.har ./src/mocks --interactive

2. Generate type-safe imports

npx mocks-to-msw generate ./src/mocks

3. Create handlers

// src/mocks/handlers.ts
import { createMockHandler } from 'mocks-to-msw';
import { mocks } from './mocks';

export const { mock, handlers } = createMockHandler<keyof typeof mocks>({
  mocks,
  debug: true,
});

4. Initialize MSW

npx msw init ./public --save

Examples

Example 1: Extract mocks from HAR

User: "I have a network.har file, extract the API mocks from it"

Action:

npx har-to-mocks network.har ./src/mocks --interactive
npx mocks-to-msw generate ./src/mocks

Output: "Extracted 12 endpoints to ./src/mocks and generated mocks.ts registry."

---

Example 2: Setup MSW for Storybook

User: "Set up the mocks to work with Storybook"

Action:

1. Install addon: npm install msw-storybook-addon --save-dev
2. Add to .storybook/main.ts:

   addons: ['msw-storybook-addon'],
   staticDirs: ['../public'],
   

3. Configure .storybook/preview.tsx:

   import { initialize, mswLoader } from 'msw-storybook-addon';
   import { handlers } from '../src/mocks/handlers';
   
   initialize();
   
   export default {
     parameters: { msw: { handlers } },
     loaders: [mswLoader],
   };
   

Output: "Configured MSW addon for Storybook. Mocks are now active in all stories."

---

Example 3: Filter specific endpoints

User: "Extract only POST requests to /api/users from the HAR"

Action:

npx har-to-mocks recording.har ./src/mocks --url "/api/users" --method POST

Output: "Extracted POST /api/users endpoint to ./src/mocks/api/users/POST.json"

---

Example 4: Override mocks in a story

User: "I want to show an error state in my UserList story"

Action: Add to story file:

export const WithError: Story = {
  parameters: {
    msw: {
      handlers: [
        http.get('*/api/users', () => HttpResponse.json(null, { status: 500 })),
      ],
    },
  },
};

Output: "Added error handler override. The story now displays the error state."

CLI Reference

Command	Description
npx har-to-mocks <har> <output> --interactive	Interactive endpoint selection
npx har-to-mocks <har> <output> --url <pattern>	Filter by URL
npx har-to-mocks <har> <output> --method <GET|POST|...>	Filter by HTTP method
npx har-to-mocks <har> <output> --dry-run	Preview without writing
npx mocks-to-msw generate <mocks-dir>	Generate type-safe imports

More Information

See REFERENCE.md for detailed documentation including:

• Recording HAR files from browser DevTools
• Full CLI options and output structure
• Complete MSW setup for browser and Node
• Storybook integration details
• Troubleshooting guide