A lightweight Chrome extension that intercepts and mocks API requests in real-time — without touching your code.

Built for frontend developers who want to test edge cases (errors, slow networks, conditional responses, real-time streams) without spinning up a backend or modifying production code.

Why Smart Mock

You're building a feature and need to see how the UI behaves when:

• the API returns a 500 error
• the network is slow (3G simulation)
• a polling endpoint returns "loading" once and then "complete"
• a GraphQL operation returns specific data
• a WebSocket sends a pong only after the client sends ping
• a header (Authorization, X-Tenant-ID) gates the response
• you want to modify the real response, not replace it
• the request times out

Doing any of this with fetch mocks in your code is annoying. Doing it with Chrome DevTools overrides is manual and not shareable. Doing it with MSW requires changing your code.

Smart Mock sits between the page and the network, intercepts requests matching your patterns, and returns whatever response you configured — including delays, errors, rotating sequences, and JS-based transforms. No code changes.

Features

Matching

• URL patterns — substring, glob (/api/users*), or regex (/\\\\/api\\\\/users\\\\/\\\\d+/)
• Method matching — GET / POST / PUT / PATCH / DELETE / ANY (segmented control with HTTP-method colors)
• Header patterns — match by Authorization: Bearer *, X-Tenant-ID: acme, etc. Substring, glob, or regex per header
• Body patterns — match POST/PUT body content