API & HTTP Tools
Test REST APIs, debug WebSocket connections, and edit OpenAPI specs. Free online API tools for developers — all 100% browser-based. Send HTTP requests, inspect responses, test WebSocket real-time communication, and design API specifications. No backend required, everything runs in your browser.
15 API & HTTP tools
- API Tools Hub — Explore REST API client, WebSocket tester, OpenAPI editor, JWT tools, and more.
- REST API Client — Send HTTP requests and view responses.
- WebSocket Client — Test WebSocket connections in real-time.
- OpenAPI Editor — Edit and preview OpenAPI specifications.
- OpenAPI Diff — Compare two OpenAPI specs side by side.
- OpenAPI Client Generator — Generate fully typed API client code for Python, TypeScript, Go, Java, C#, and more from your OpenAPI spec.
- JSON Mock Data Generator — Generate realistic mock JSON responses for REST API endpoints using Faker.js.
- URL Encoder — URL-encode query parameters for API requests.
- JWT Encoder — Create JWT tokens for API authentication.
- What is a REST API? — Learn REST API principles, methods, and best practices.
- What is WebSocket? — Learn how WebSocket enables real-time communication.
- What is GraphQL? — Learn GraphQL queries, mutations, subscriptions, and schema design.
- What is OpenAPI? — Learn OpenAPI specification structure, paths, schemas, and documentation.
- How to Fix CORS Errors — Learn how to fix CORS errors with headers, preflight requests, and server config.
- How to Use cURL — Complete guide to using cURL for API testing and HTTP requests.