Open-Source HTTP Interceptor & Mocking Tool

Loved by 300k+ developers — intercept, modify, mock, and debug HTTP(S) traffic from your browser and desktop apps.

Part of the Requestly ecosystem — Requestly API Client · HTTP Interceptor · HTTP Interceptor Desktop · Docs

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Requestly HTTP Interceptor is an open-source HTTP interception and traffic debugging tool that helps developers intercept, inspect, monitor, and modify HTTP(S) traffic directly from browsers and desktop apps.

It supports powerful debugging workflows including request/response modification, API mocking, traffic inspection, and environment overrides without requiring complex proxy or VPN setup.

Trusted by 300,000+ developers and 11,000+ companies worldwide.

Intercept, monitor, and modify HTTP(S) requests and responses in real time.

📚 Docs: https://docs.requestly.com/general/http-interceptor/overview

• Redirect URLs and environments
• Map local files and remote resources
• Modify request and response headers
• Override API request and response bodies
• Inject custom JavaScript into webpages
• Debug and inspect network traffic
• Capture traffic from browsers, mobile apps, and desktop apps

• Redirect production traffic to local or staging
• Test feature flags and edge cases
• Override APIs during frontend development
• Replace analytics or third-party scripts
• Simulate backend failures and latency

Build and test frontend applications without waiting for backend APIs.

📚 Docs: https://docs.requestly.com/general/api-mocking/api-mocking

• Local API mocking
• Cloud-hosted mocks
• Static & dynamic response overrides
• GraphQL request targeting
• Bulk mock generation from sessions
• Mock APIs in Cypress, Playwright, Selenium, and CI pipelines

• Frontend parallel development
• E2E testing
• QA & staging simulations
• Offline development
• Contract testing

Easily migrate existing configurations from other tools.

• Charles Proxy
• ModHeader
• Resource Override

• https://docs.requestly.com/general/imports/charles-proxy
• https://docs.requestly.com/general/imports/modheader
• https://docs.requestly.com/general/imports/resource-override

Pick the install that matches how you work — a lightweight browser extension for in-browser interception, or the desktop app for system-wide traffic capture.

Install Requestly directly into your browser to start intercepting and modifying HTTP(S) traffic in seconds.

Use the desktop app to capture traffic across browsers, mobile devices, and any desktop application — ideal for debugging, mocking APIs, and sessions.

The desktop app source code lives in a separate repo: requestly/http-interceptor-desktop-app.

This repository contains:

• Browser Extension (browser-extension/) — Chrome, Firefox, Edge (Manifest V3)
• Web App UI (app/) — the dashboard at app.requestly.com
• Core Traffic Interceptor Logic

Follow the setup guide:

👉 Getting Started

• Desktop App — Electron shell for system-wide interception
• Mock Server
• Web SDK
• Proxy Engine
• Automation integrations — Selenium / Playwright / Puppeteer

We welcome contributions from the community.

Whether you're fixing bugs, improving docs, or building new features, your contributions help make Requestly better for developers everywhere.

1. Explore open issues
2. Read the contributing guidelines
3. Submit a pull request
4. Join the community discussions

• Issues
• Contributing Guide
• Community

• 📚 Documentation: https://docs.requestly.com/general/http-interceptor/overview
• 🔐 Security & Privacy: https://docs.requestly.com/security-privacy/
• 💬 Community: https://get.requestly.com/join-community
• 📧 Email: contact@requestly.com
• ❓ StackOverflow: https://stackoverflow.com/questions/tagged/requestly

The open-source source code for the Requestly HTTP Interceptor extension and web app lives here at requestly/interceptor. Previously this code lived under requestly/requestly; that URL is now the community and issue tracker for the Requestly API Client.

The HTTP Interceptor remains fully open source and actively maintained. Contributions, bug reports, and feature requests are welcome here.

Requestly is built to make debugging and testing faster and simpler.

From HTTP interception and API mocking, Requestly gives developers everything needed to debug and ship confidently.

• Brand asset paths (https://github.com/requestly/interceptor/blob/master/app/src/assets/img/brand/...) — verify these files exist in the new repo after the codebase migration
• Screenshot URLs (currently github.com/user-attachments/...) — verify they remain accessible from the new repo context (user-attachments are organization-scoped, should be fine)
• Decide whether to keep discussions link (current README has it; some teams disable Discussions to reduce triage surface)