Open Source

Intercept & Modify
Request Body in Real Time.

Change the way you test APIs. Check the API responses with different inputs, find edge cases, simulate API errors.

4.8 ⭐ 1,000+ reviews , 200,000+ developers

Override XHR/fetch Requests

Using Requestly Modify Request Body rule, you can override the API requests triggered by XHR/fetch. No need to hardcode APIs in frontend code anymore.

Test error paths in your code

Modify API request body to trigger different error paths in your codebase and test the flows without changing anything on backend. e.g. Simulate Payment Timeout Issue, Item out of stock Issue, etc.

1-Click Sharing

Use-Cases in teams are very similar so Requestly makes it easier to share the rules with each other and collaborate faster.

Trusted by developers at

Application and use cases

Here’s how you can use Requestly’s Modify Response feature in your daily workflow

Static Response

Allows you to intercept and replace the original server response with a predefined fixed JSON or string response

Download for other platforms/browsers

Dynamic response

Gives ability to modify the server response programmatically using JavaScript. Write custom JavaScript code that runs on the intercepted response and manipulate its content.

Download for other platforms/browsers

Fake status code

Enables you to change the HTTP status code of a server response. By modifying the status code, you can simulate different server responses without actually altering the content.

Download for other platforms/browsers

Intercept & Modify HTTP Requests

Boost Your Web Development: Advanced Tools for Seamless Debugging.

Redirect URL (Map Remote)

Redirect a request URL to another URL. e.g. Load local scripts in the production sites for faster debugging.

Override API Response

Test edge cases in your app by simulating API responses‍. Override XHR, fetch and AJAX responses.

Inject Custom Scripts

Add Custom JavaScript (JS) to Hide unwanted sections, add action buttons, inject your own libraries, etc.

Modify HTTP Headers

Add, Delete, Override Request & Response Headers. Can be used to remove X-Frame-Options, Content-Security-Policy, CORS Issues, etc.

Modify Query Params

Insert, Modify or Delete query parameters for URLs (or matching pattern). Burst cache for a request by assigning it a newer version.

Delay HTTP Requests

Simulate lag / delay to the response from specific URLs in a single click by using Requestly’s Delay Request Rule. No need to modify actual server.

More from Requestly

An open-source platform that speeds up your web development cycle 10X faster.

Session Recording

Data rich bug reporting with Network logs, Console logs, Session Video and environment details. Share it with your Engineering team for faster debugging.

Download for other platforms/browsers

Mock API Server

Generate custom API responses without actually having a pre-built API or a backend server. Edit Content-Type, Status Code, Headers, and Response body easily on the Mock Server.

Download for other platforms/browsers

Web-based API Client

A comprehensive and web-based tool for modifying and testing APIs. You can test the Mock APIs you’re creating here to fast track your development lifecycle.

Download for other platforms/browsers

For the developers, by the developers ❤️

From Debug to Deploy: Developers Trust Requestly

Awesome tool. I use it almost daily for my projects to modify request body, headers, etc. Would recommend it to every frontend developer out there. Thank me later 🙂 (Case Study)

Harsh Vats

Frontend Engineer at PingSafe

Simple UI, Huge Impact Loved the intuitive UI for request body modification. Helped in confirming backend security with my senior engineer, even bested Postman Interceptor in some cases.