Professional REST API Client - Test, Debug & Document APIs Instantly in Your Browser
Welcome to the most powerful free online API testing tool available in 2025. Our browser-based REST API client provides developers, QA engineers, and API enthusiasts with a comprehensive platform to test, debug, and document APIs without any downloads or installations. Whether you're testing REST APIs, GraphQL endpoints, SOAP services, or webhooks, our tool offers enterprise-grade features completely free of charge.
In today's fast-paced development environment, having quick access to reliable API testing tools is crucial. Our online API tester eliminates the friction of downloading software, managing licenses, or dealing with complex installations. Simply open your browser and start testing APIs immediately. This makes it perfect for quick tests, client presentations, educational purposes, or when working on shared computers.
Test APIs directly in your browser. Works on Windows, Mac, Linux, and even mobile devices. No downloads, no setup, just instant access.
All API requests are made directly from your browser. Your sensitive data never passes through our servers, ensuring complete privacy and security.
Optimized for performance with instant response visualization, real-time request timing, and efficient data handling for large payloads.
No hidden costs, no premium tiers, no trial periods. All features are available for free forever with unlimited API requests.
Our REST API client supports all standard HTTP methods essential for modern API development: GET, POST, PUT, PATCH, DELETE, HEAD, and OPTIONS. Whether you're retrieving data, creating resources, updating records, or checking server capabilities, our tool handles every HTTP verb with precision. This complete method support makes it ideal for testing RESTful services, microservices architectures, and traditional web APIs.
Configure every aspect of your API requests with our intuitive interface:
Security is paramount in API development. Our tool provides comprehensive authentication support:
Understanding API responses is critical for debugging and development. Our tool provides automatic formatting and syntax highlighting for JSON and XML responses, making complex data structures easy to read and analyze. The response viewer includes:
Every API request includes detailed performance metrics showing exactly how long the request took to complete. This is invaluable for identifying slow endpoints, comparing API performance across different configurations, and ensuring your APIs meet performance requirements. Monitor response times to optimize your API calls and identify bottlenecks in your service architecture.
Developers use our tool throughout the API development lifecycle. During initial development, quickly test endpoints as you build them. During integration, verify that APIs work correctly with different parameters and authentication methods. During debugging, isolate issues by testing individual endpoints with various configurations. The immediate feedback loop helps identify problems early and speeds up development.
Quality assurance teams rely on our API testing tool for comprehensive endpoint validation. Test positive and negative scenarios, verify error handling, validate response formats, check status codes, and ensure APIs meet specifications. The ability to modify headers and body content makes it easy to test edge cases and potential security vulnerabilities.
Whether you're learning about APIs or documenting endpoints for your team, our tool provides a hands-on environment to explore API functionality. Teachers use it in classrooms to demonstrate HTTP concepts, REST principles, and API design patterns. Technical writers use it to verify documentation accuracy and create example requests for API guides.
When integrating third-party APIs like payment gateways, social media platforms, or SaaS services, our tool lets you experiment with endpoints before writing code. Test authentication flows, understand response structures, and verify your API keys work correctly. This exploratory testing prevents costly mistakes and reduces integration time.
While Postman is a popular choice for API testing, our browser-based tool offers significant advantages for many use cases:
When testing a new API, begin with simple GET requests to understand the data structure and response format. This helps you familiarize yourself with the API without risking data modifications. Examine the response headers, status codes, and body structure before moving to more complex operations.
Don't just test the happy path. Send invalid data, missing required fields, malformed JSON, and incorrect authentication to verify the API handles errors gracefully. Check that appropriate status codes (400, 401, 403, 404, 500) are returned and error messages are helpful.
Ensure API responses match expected formats and contain all required fields. Check data types, validate nested objects, and verify array contents. Consistent response structures are crucial for reliable client applications.
Pay attention to response times, especially for production APIs. Slow responses can indicate database issues, inefficient queries, or scaling problems. Use our response time metrics to establish performance baselines and identify degradation.
REST (Representational State Transfer) is the most common API architecture. Our tool excels at testing RESTful endpoints with full support for resource-based URLs, standard HTTP methods, and JSON/XML payloads. Test CRUD operations (Create, Read, Update, Delete) with ease using POST, GET, PUT/PATCH, and DELETE methods respectively.
Many APIs require authentication before accessing protected resources. Test OAuth 2.0 flows by first obtaining access tokens, then using those tokens in subsequent requests. Verify token expiration handling and refresh token mechanisms. Test that unauthorized requests receive appropriate 401 responses.
While primarily designed for REST, our tool can test GraphQL endpoints by sending POST requests with GraphQL queries in the request body. Set Content-Type to application/json and structure your query properly in the body editor.
Webhooks send HTTP requests to your endpoints when events occur. Use our tool to simulate webhook payloads and test how your application handles incoming data. This is especially useful when developing webhook receivers for services like GitHub, Stripe, or Slack.
Our API testing tool is built with modern web technologies ensuring compatibility across all major browsers including Chrome, Firefox, Safari, Edge, and Opera. It uses the Fetch API for making HTTP requests, providing native support for CORS, redirects, and various response types. The tool works on desktop and mobile browsers, though desktop is recommended for optimal experience.
When testing APIs from a browser, Cross-Origin Resource Sharing (CORS) restrictions may apply. If an API doesn't allow requests from browser origins, you'll need to use browser extensions to disable CORS temporarily for testing purposes, or test from a server-side environment. Remember that CORS is a browser security feature, so production APIs should have appropriate CORS configurations.
Yes! Our online API testing tool is completely free with no hidden charges, no premium features locked behind paywalls, and no usage limits. We believe developers should have access to quality tools regardless of budget.
No account required! Start testing APIs immediately without any registration or login process. Your privacy is important to us.
Absolutely. All API requests are made directly from your browser to the target API. No data passes through our servers. Your API keys, tokens, and sensitive information stay completely private.
Yes, you can test APIs running on localhost or your local network. Make sure the API allows requests from your browser origin.
Current version supports text-based body types including JSON, XML, and form data. Binary file uploads are planned for future releases.
Currently, requests are not persisted. For recurring tests, we recommend bookmarking the page and manually entering your configurations, or copying the curl command equivalent.
Ready to start testing? Follow these simple steps:
Many APIs implement pagination to handle large datasets efficiently. Test pagination by adding query parameters like page, limit, offset, or cursor to your requests. Verify that the API returns the correct number of items per page, includes navigation links (next, previous, first, last), and provides total count information. Check edge cases like requesting page numbers beyond available data.
APIs often implement rate limiting to prevent abuse and ensure fair usage. Test how your API handles rate limits by sending multiple rapid requests. Look for HTTP 429 (Too Many Requests) responses and check for rate limit headers like X-RateLimit-Limit, X-RateLimit-Remaining, and X-RateLimit-Reset. Understanding rate limits is crucial for building resilient client applications.
Test how APIs handle different content types using the Accept header. Some APIs support multiple formats like JSON, XML, or CSV. Send requests with different Accept headers (application/json, application/xml, text/csv) to verify the API responds with the correct format. Also test the Content-Type header for POST/PUT requests to ensure proper request parsing.
APIs evolve over time, and versioning ensures backward compatibility. Test different API versions by modifying version numbers in URLs (e.g., /v1/users vs /v2/users) or headers (Accept: application/vnd.api+json;version=2). Verify that deprecated endpoints return appropriate warnings and that version changes don't break existing integrations.
Testing payment APIs requires extra caution. Use sandbox environments provided by payment processors like Stripe, PayPal, or Square. Test various payment scenarios: successful charges, declined cards, expired cards, insufficient funds, and refund processing. Verify that sensitive card data is never exposed in responses and that idempotency keys prevent duplicate charges.
Social platforms like Twitter, Facebook, Instagram, and LinkedIn provide APIs for integration. Test authentication flows using OAuth 2.0, verify posting capabilities, test media uploads, and check rate limits. Social APIs often have strict usage policies, so understanding their testing environments and limitations is essential.
AWS, Google Cloud, Azure, and other cloud providers offer extensive APIs for infrastructure management. Test compute, storage, and networking APIs carefully in development environments. Verify IAM permissions, test resource lifecycle operations (create, read, update, delete), and monitor costs during testing to avoid unexpected charges.
APIs from Twilio, SendGrid, Mailgun, and similar services enable email, SMS, and voice communications. Test message delivery, verify webhook callbacks, check delivery receipts, and validate templating functionality. Always use test credentials and phone numbers to avoid sending actual messages during development.
Postman is a comprehensive desktop application with collections, environments, and team collaboration features. Our browser-based tool offers instant access without installation, making it perfect for quick tests, educational purposes, and situations where you can't install software. Choose Postman for complex test suites and team workflows; choose our tool for simplicity and universal access.
Insomnia provides a sleek interface with GraphQL support and design-first workflows. Like Postman, it requires installation. Our tool matches Insomnia's core testing capabilities while eliminating setup requirements. Use Insomnia for GraphQL-heavy projects; use our tool for REST APIs and immediate testing needs.
cURL is a powerful command-line tool beloved by developers. It offers maximum flexibility but requires memorizing syntax and flags. Our visual interface makes API testing accessible to non-technical users while still providing all essential features. Use cURL for scripting and automation; use our tool for interactive testing and learning.
HTTPie improves on cURL with human-friendly syntax and colored output. It's excellent for terminal users but still requires command-line comfort. Our browser tool provides similar usability with a graphical interface. Use HTTPie for terminal workflows; use our tool for visual feedback and easier sharing with team members.
Test Express.js, Fastify, or Koa APIs by pointing our tool to your local development server. JavaScript APIs often use JSON extensively, making our JSON editor perfect for crafting requests. Test CORS configurations, middleware behavior, and error handling. Verify that APIs return appropriate content types and status codes.
Python web frameworks power countless APIs. Test Django REST Framework endpoints, Flask-RESTful APIs, or FastAPI services. Python APIs often include automatic documentation (Swagger/OpenAPI), which complements our testing tool. Verify serialization, authentication middleware, and database query efficiency.
Enterprise Java APIs built with Spring Boot benefit from comprehensive testing. Test REST controllers, verify Spring Security configurations, check exception handling, and validate data binding. Java APIs often have complex authentication schemes that our tool's auth features handle elegantly.
Rails API-only applications provide clean RESTful interfaces. Test Active Model Serializers, verify routing, check parameter filtering, and validate response formats. Rails conventions make API testing predictable, and our tool's structure aligns well with Rails RESTful design.
PHP frameworks offer robust API development capabilities. Test Laravel API resources, verify middleware authentication, check rate limiting, and validate request validation rules. PHP APIs often integrate with various databases, making thorough endpoint testing crucial.
Go's performance makes it popular for API development. Test Gin, Echo, or standard library HTTP handlers. Verify JSON marshaling, test middleware chains, check error responses, and validate concurrent request handling. Go's strong typing means APIs often have predictable structures perfect for testing.
Microsoft's .NET ecosystem provides powerful API frameworks. Test ASP.NET Core Web APIs, verify attribute routing, check model binding, validate authentication with Identity, and test Entity Framework integration. .NET APIs often include built-in OpenAPI documentation.
Mobile applications rely heavily on APIs for data synchronization, authentication, and content delivery. Test mobile APIs for offline scenarios, network interruptions, and varying connection speeds. Verify that APIs handle token refresh properly, implement proper caching headers, and return appropriate error messages for mobile users. Consider payload size optimization as mobile bandwidth can be limited.
When testing APIs for iOS apps, verify URLSession compatibility, test certificate pinning if implemented, and check JSON parsing with Codable. iOS apps often use specific authentication patterns like Apple Sign-In that require careful testing.
Android API integration uses Retrofit, OkHttp, or Volley. Test these libraries' behaviors by verifying API responses match expected formats. Check that APIs handle Android's aggressive battery optimization and background restrictions properly.
Test for weak authentication by attempting requests without credentials, with expired tokens, or with tokens from different users. Verify that APIs return 401 Unauthorized for missing auth and 403 Forbidden for insufficient permissions. Check that error messages don't leak sensitive information about user existence or system architecture.
Security vulnerabilities often stem from poor input validation. Test APIs with malformed JSON, extremely long strings, special characters, SQL injection attempts, XSS payloads, and null values. Well-designed APIs should reject invalid input gracefully without exposing system internals.
All production APIs should enforce HTTPS. Test that HTTP requests are redirected to HTTPS or rejected entirely. Verify that sensitive data like passwords, tokens, and personal information are never transmitted over unencrypted connections.
Test Cross-Origin Resource Sharing policies to ensure APIs allow requests from authorized domains only. Overly permissive CORS settings can expose APIs to unauthorized access. Verify that preflight requests (OPTIONS) return correct headers and that credentials are handled securely.
While our tool focuses on functional testing, understanding performance is crucial. Use response time metrics to establish performance baselines. For dedicated load testing, consider tools like Apache JMeter, k6, or Gatling that can simulate thousands of concurrent users. However, our tool is perfect for initial performance validation and identifying obviously slow endpoints.
Industry standards suggest APIs should respond within:
Many modern APIs provide OpenAPI specifications describing endpoints, parameters, and responses. Use these specifications to guide your testing. Our tool complements API documentation by providing hands-on testing of documented endpoints. Compare actual responses with documented schemas to identify discrepancies.
API Blueprint is another documentation format focusing on markdown-based descriptions. Use our tool to validate that implemented APIs match their blueprints, testing each documented endpoint, parameter, and response format.
While our browser tool excels at manual testing, modern development practices require automated API testing in CI/CD pipelines. For automation, consider integrating tools like Newman (Postman's CLI), REST Assured, or SuperTest into your build process. Use our tool during development for exploratory testing and debugging, then codify critical tests for automation.
Endpoint: POST /api/users/register
Test valid registration with name, email, password. Verify 201 Created response with user object. Test duplicate email returns 409 Conflict. Test weak password returns 400 Bad Request with validation errors. Test missing required fields returns 400 with field-specific errors.
Endpoint: POST /api/auth/login
Send credentials, verify 200 OK with access and refresh tokens. Use access token in Authorization header for protected endpoint. Verify 401 when token missing. Test token refresh mechanism by sending refresh token to /api/auth/refresh. Verify logout invalidates tokens.
Endpoint: GET /api/products?category=electronics&price_min=100&price_max=500
Verify results match filter criteria. Test multiple filters simultaneously. Test invalid filter values return 400. Test filtering with sorting and pagination combined. Verify empty results when no matches found.
If you see CORS errors in browser console, the API hasn't configured CORS headers properly. This is common when testing local development APIs. Solutions: enable CORS in API code, use browser extensions to disable CORS temporarily for testing, or proxy requests through a server that adds CORS headers.
Double-check URL spelling, verify the endpoint exists, check for trailing slashes, confirm correct HTTP method, and verify API versioning in URL or headers. APIs are case-sensitive.
Authentication failed. Verify token/credentials are correct, check token hasn't expired, ensure Authorization header format is correct (Bearer token format), and confirm you're using the right authentication method.
Server-side issue. Check API logs for specific error, verify request body format matches API expectations, confirm all required fields are present, and ensure data types match API specifications. This often indicates a bug in API code.
API testing continues evolving with emerging technologies. GraphQL offers more flexible querying, requiring different testing approaches. gRPC provides high-performance RPC with Protocol Buffers, changing how we think about API contracts. WebSocket APIs enable real-time bidirectional communication, requiring persistent connection testing. Our tool adapts to these changes, providing timeless testing capabilities for whatever APIs the future brings.
To master API testing, explore these concepts: HTTP protocol fundamentals, REST architectural constraints, JSON and XML data formats, authentication and authorization patterns (OAuth 2.0, JWT, API keys), HTTP status codes and their meanings, idempotency and safe methods, API design best practices, versioning strategies, error handling patterns, and rate limiting implementations.
Our free online API testing tool provides everything you need for comprehensive API testing without the overhead of desktop applications. Whether you're a developer building APIs, a QA engineer validating endpoints, a student learning web development, or a technical writer documenting services, this tool offers professional-grade capabilities in an accessible, browser-based interface. Start testing your APIs now with zero setup time and unlimited requests. Bookmark this page for instant access whenever you need to test an API endpoint.
Ready to test your first API? Enter an endpoint URL above and click Send Request to get started!
Try these free public APIs to get started with our testing tool:
API (Application Programming Interface): A set of rules and protocols that allows different software applications to communicate with each other.
REST (Representational State Transfer): An architectural style for designing networked applications using HTTP methods and stateless communication.
Endpoint: A specific URL where an API can be accessed by a client application. Each endpoint typically represents a specific resource or action.
HTTP Methods: Standard operations in HTTP protocol - GET (retrieve), POST (create), PUT (update/replace), PATCH (partial update), DELETE (remove).
Headers: Metadata sent with HTTP requests and responses containing information about content type, authentication, caching, and more.
Query Parameters: Key-value pairs appended to URLs after a question mark (?) used to filter, sort, or modify API responses.
Request Body: Data sent with POST, PUT, or PATCH requests, typically in JSON or XML format, containing information to create or update resources.
Status Code: Three-digit numbers returned by servers indicating the result of HTTP requests (200 = success, 404 = not found, 500 = server error).
CORS (Cross-Origin Resource Sharing): Security feature that restricts web pages from making requests to domains different from the one serving the page.
Bearer Token: Authentication method where a token is included in the Authorization header to verify the requester's identity.
JSON (JavaScript Object Notation): Lightweight data format widely used for API communication due to its readability and ease of parsing.
OAuth 2.0: Industry-standard protocol for authorization allowing applications to obtain limited access to user accounts.
Rate Limiting: Restricting the number of API requests a client can make within a specific time period to prevent abuse.
Idempotency: Property where multiple identical requests have the same effect as a single request (important for PUT and DELETE methods).
This free API testing tool is designed to serve the developer community. We continuously improve based on user feedback and emerging API testing needs. While we don't offer direct support, the tool is intuitive and self-explanatory for anyone familiar with APIs.
We respect your privacy. This tool operates entirely in your browser using client-side JavaScript. No API requests, responses, or credentials pass through our servers. All data remains on your device. We don't collect, store, or transmit any information about your API testing activities. Your API keys, tokens, and sensitive data are completely private and secure.
This API testing tool works best on modern browsers with JavaScript enabled. Recommended browsers include:
While our tool is powerful, please note these limitations:
While we believe our tool serves most API testing needs, here are scenarios where other tools might be better:
Our API testing tool is continuously updated with new features and improvements. Recent additions include enhanced authentication options, improved response formatting, better error handling, and expanded documentation. Check back regularly for new capabilities.
This tool is perfect for educational purposes. Teachers and instructors can use it to demonstrate HTTP concepts, REST principles, and API integration without requiring students to install software. The visual interface helps beginners understand request structure, headers, authentication, and response formats.
API testing is an essential skill for modern software development. Whether you're building microservices, integrating third-party services, or developing mobile applications, understanding how to test APIs effectively will make you a better developer. Our free online API testing tool removes barriers to entry, providing professional-grade testing capabilities without cost or complexity. Bookmark this page and make it your go-to resource for quick API validation, debugging, and exploration.
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