What is an API Tester?
An API tester is a developer tool that allows you to send HTTP requests to any Application Programming Interface (API) to verify its responses, headers, and performance. Whether you are building a new RESTful backend or integrating a third-party service, an API tester is essential for debugging and ensuring seamless communication between software components.
Why use our Browser-Based REST Client?
Unlike bulky desktop applications like Postman or Insomnia, our free online API Tester runs entirely within your browser. There is no software to install, no sign-up required, and no paywalls. You can test your endpoints instantly from any device. It supports all standard HTTP methods, custom headers, query parameters, multiple body formats, and various authentication schemes.
Key Features
- HTTP methods: GET, POST, PUT, PATCH, DELETE, HEAD with JSON, GraphQL, form-data, and URL-encoded bodies.
- Auth: Bearer, Basic, and API key (header or query).
- Environments:
{{variable}}substitution across URL, headers, and body. - Collections & full history: Save and reload complete requests (not just the URL).
- Import: Paste cURL or import Postman Collection v2 JSON.
- Tests: Lightweight assertions (status, body contains, JSON path, response time).
- Code export: cURL, JavaScript fetch, and Python requests.
- Smart response tools: JSON highlighting, search, download, extract values into env vars.
What we don't have (vs Postman)
Postman is a full platform: team workspaces, cloud sync, mock servers, OAuth wizards, gRPC/WebSocket clients, and automated CI collections. Our tool is browser-only—no account, no server proxy—so CORS still applies. For local APIs without CORS headers, use the generated cURL in your terminal or fix Access-Control-Allow-Origin on the API.
Frequently Asked Questions (FAQ)
Is my data secure when using this tool?
Yes. All API requests are made directly from your browser to the target server. We do not proxy, log, or store your requests, headers, or payloads on our servers. Your local history and collections are saved exclusively in your browser's localStorage.
Why am I getting a CORS error?
Cross-Origin Resource Sharing (CORS) is a browser security feature. If the API server you are testing does not explicitly allow requests from https://www.slashgit.com, your browser will block the request. To bypass this for local development, you may need to configure your server to return the appropriate Access-Control-Allow-Origin headers or use a browser extension that temporarily disables CORS checks.
Does this tool support GraphQL or WebSockets?
Use the GraphQL body type for standard POST requests with query and variables. Native WebSocket clients are not supported in the browser tool yet.