Rex — API Client

A fast, keyboard-driven REST API client for developers. Test APIs without leaving your browser.

Rex is a full-featured API client that lives in your browser. Test REST APIs, GraphQL endpoints, WebSockets, and Server-Sent Events without switching to a separate app. If you've ever wished Postman was just a tab away, Rex is for you. Built for developers who spend their day in the browser — debugging frontend requests, testing backend endpoints, or exploring third-party APIs. Open Rex as a new tab or from DevTools, and you're ready to go. No account required, no cloud sync, no sign-up wall. Everything stays local on your machine. WHY REX? Most API clients are heavyweight desktop apps or cloud-first tools that require accounts and subscriptions just to send a GET request. Rex takes a different approach: it's a browser extension that's always one click away, stores everything locally in IndexedDB, and gives you professional-grade tooling without the overhead. Because Rex runs inside Chrome, it has access to things external tools don't — your browser cookies, your active sessions, your DevTools network requests. That means you can test authenticated APIs without manually copying tokens, inspect cookies per domain, and import requests straight from the Network tab. WHAT YOU CAN DO WITH REX Send HTTP Requests Support for GET, POST, PUT, PATCH, DELETE, HEAD, and OPTIONS. Configure query parameters, headers, and request bodies with a visual editor or switch to bulk-edit mode for quick pasting. Rex auto-detects Content-Type and provides real-time validation for JSON bodies. Work With Multiple Body Types Six body editor modes: JSON (with syntax highlighting and format-on-click), raw text, form data with file uploads, URL-encoded forms, GraphQL with schema-aware autocomplete, or no body at all. The editor adapts to what you're sending. Authenticate Any Way You Need Rex supports Bearer tokens, Basic Auth, API Key (header or query), OAuth 2.0 (Authorization Code, Client Credentials, PKCE, and token refresh), AWS Signature V4, and Digest Authentication. OAuth flows run entirely in the browser with automatic token management and expiration tracking. View Responses in Context Responses render based on content type — JSON is syntax-highlighted and auto-formatted, HTML gets an inline iframe preview alongside source view, images display inline with dimensions, PDFs render in a built-in viewer, and binary data shows a hex dump with download option. XML is auto-formatted. Every response shows status code, response time, and size at a glance with color-coded status badges. Stream in Real Time Connect to Server-Sent Events endpoints and watch events arrive in real time with timestamps. Open WebSocket connections and send/receive messages with a live message log showing direction, timing, and payload size. Both modes support clean connect/disconnect lifecycle management. ORGANIZE YOUR WORK Collections Save requests into collections and organize them however you like. Drag and drop to reorder requests or move them between collections. Duplicate, rename, or delete with right-click. Collections persist across sessions and remember their expanded/collapsed state. Tabs Work on multiple requests at once with tabs. Cmd+T opens a new tab, Cmd+W closes the current one. Each tab maintains its own request configuration and response — switch between them without losing state. Environments Create environments (development, staging, production) with key-value variables. Reference them anywhere in your requests with {{variableName}} syntax — in URLs, headers, body, or query params. Rex shows visual indicators for resolved and unresolved variables so you always know what's being substituted. Switch environments with one click. History Every request you send is recorded with its full response. Search through history, and compare any two responses side-by-side with a built-in diff viewer that highlights changes in body content, headers, status codes, response times, and sizes. POWER FEATURES Request Chaining Build sequences of dependent API requests and run them in order. Configure variable overrides, pre-request scripts, and test scripts for each step. Choose how to handle failures — stop the chain, skip the step, or retry with configurable attempts. Watch execution progress in real time with pass/fail indicators for each step. Perfect for testing authentication flows, CRUD sequences, or any multi-step API workflow. Pre-Request & Test Scripts Write JavaScript that runs before a request is sent or after a response arrives. The scripting API gives you full control: - Modify headers dynamically with rex.setHeader() - Set and read variables with rex.setVariable() and rex.getVariable() - Access environment variables with rex.env.get() - Inspect responses with rex.response.status, rex.response.json(), rex.response.headers - Write test assertions with rex.test() that report pass/fail results The script editor includes autocomplete, hover documentation, and parameter hints for the entire Rex scripting API. GraphQL A dedicated GraphQL mode with a query editor, variables pane, and automatic schema introspection. Point Rex at a GraphQL endpoint, fetch the schema, and get real-time autocomplete for types, fields, queries, mutations, and fragments — all powered by your actual API schema. Code Generation Turn any request into working code. Generate snippets in JavaScript (Fetch, Axios, Node.js http), Python (requests, httpx), cURL, and more. Copy to clipboard and paste directly into your project. API Documentation Browser Load an OpenAPI 3.x or Swagger 2.0 spec (from a URL or file upload) and browse all endpoints organized by tag. Search by path, method, or operation name. View parameters, request body schemas, response schemas for every status code, and security requirements. Hit "Try it" on any endpoint to load it into the request builder with everything pre-filled. Diff Viewer Select any two history entries and compare them side by side. The diff viewer shows line-by-line changes in response bodies (additions in green, removals in red), highlights changed headers, and compares status codes, response times, and payload sizes. Useful for regression testing or tracking how an API response changes over time. Cookie Editor Inspect cookies for any domain directly inside Rex. See cookie values, flags (HttpOnly, Secure), and delete individual cookies. Because Rex runs as a Chrome extension, it has direct access to your browser's cookie jar — no workarounds needed. IMPORT & EXPORT Bring your existing work into Rex or take it with you: - Import from Postman Collections (v2.1), OpenAPI 3.x / Swagger 2.0 (JSON & YAML), or HAR files - Export collections as Postman format or history as HAR 1.2 - Copy any request as a cURL command, JSON, or a shareable Rex link - Paste a cURL command into Rex and it auto-parses into a full request Rex auto-detects the format when you import, validates the data, and reports exactly what was imported with any warnings. DEVELOPER EXPERIENCE Rex is keyboard-driven by design: - Cmd+Enter: Send request - Cmd+S: Save request - Cmd+B: Toggle sidebar The DevTools panel lets you capture network requests from any page and import them directly into your collections — no manual re-entry needed. PRIVACY & DATA Rex stores all data locally in your browser using IndexedDB. Your requests, collections, environments, and history never leave your machine. There is no account system, no telemetry, no cloud storage. The extension requests host permissions (<all_urls>) solely to send API requests to whatever endpoints you specify — it never makes requests on its own. Rex is free to use with no feature gates or usage limits.