Online API Clients and OpenAPI UI Tools
These online clients and OpenAPI UIs run in your browser so you can make quick requests, inspect OpenAPI files, and compare how different tools present the same API description.
Browser tools are convenient for learning and quick checks. They are still limited by browser security rules such as CORS, and the request you can send is often shaped by the tool and by the OpenAPI file it renders.
Hosted Online Clients
- Basic Client - a deliberately simple REST API client for sending custom methods, URLs, headers, and bodies without needing an OpenAPI file.
- Online Swagger UI - Swagger UI with URL and file loading, plus optional tester OpenAPI conversion for less restrictive exploratory requests.
- OpenAPI Explorer - an embeddable web component that renders resources, models, generated examples, and browser API calls from an OpenAPI file.
- Scalar - a modern OpenAPI reference and API client style experience with request examples and API documentation navigation.
- Stoplight Elements - embeddable OpenAPI documentation components with navigation, schemas, code samples, and an interactive API console.
- Zudoku - a developer portal and API reference framework that can render OpenAPI powered documentation from a URL.
- Redoc - a polished OpenAPI documentation viewer for reading and navigating API reference content.
- OpenAPI Tester Converter - a browser tool for creating a less restrictive tester OpenAPI file to import into Swagger UI or other clients.
How The Tools Differ
Use the Basic Client when you want the most freedom from this site. It is not driven by an OpenAPI file, so you can send unusual methods, malformed payloads, missing fields, or hand-built requests as long as the browser allows them.
Use Swagger UI, OpenAPI Explorer, Scalar, Stoplight Elements, or Zudoku when you want an OpenAPI file rendered as interactive documentation. These tools are useful for discovering endpoints, schemas, authentication information, request examples, and normal request flows.
Use Redoc when you want to read the API reference. The open source Redoc experience is primarily a viewer, not a request-sending API client, so pair it with the Basic Client, Swagger UI, or a desktop REST client when you need to send test traffic.
Use the OpenAPI Tester Converter when a strict OpenAPI description gets in the way of testing. The converter can remove common schema restrictions and add missing HTTP methods so OpenAPI-driven UIs can show more exploratory request shapes.
CORS And Browser Limits
Because these online tools run in the browser, they can only load OpenAPI files and send API requests that the browser is allowed to access.
CORS means Cross-Origin Resource Sharing. It is the browser rule that controls whether JavaScript from one origin can call another origin. If an OpenAPI file or target API does not allow this site, the browser may block loading the file, block a preflight request, or hide parts of the response.
If an OpenAPI URL does not load, download the file and open it from disk using the file chooser on the tool page. Local files are read by your browser and are not uploaded to API Challenges.
If a request works in cURL, Bruno, Postman, or another desktop client but fails in a browser tool, check the browser developer tools console and Network tab for CORS messages.
Testing With Browser Developer Tools
When you send requests from an online client, open your browser developer tools and use the Network tab to see the raw HTTP request and response details.
The Network tab shows request method, URL, headers, payload, status code, response headers, response body, redirects, timing, and browser-level failures. This helps you compare what the online client displays with what the browser actually sent and received.
Most browsers can export captured Network activity as a HAR file. A HAR file records HTTP Archive data for the session, which can help you keep evidence of exploratory API testing.
When To Use A Desktop REST API Client
Online clients are useful for fast learning and quick checks, but desktop API clients and command line tools are still important for deeper testing.
Use a desktop client when you need to avoid CORS limits, configure a proxy, send browser-blocked methods such as TRACE, manage large collections, or keep detailed testing evidence across sessions. Start with the REST/HTTP Clients overview, compare the summary reviews, or read detailed notes for Bruno, cURL, Postman, Insomnia, and Yaak.
For deeper investigation, use an HTTP proxy alongside your client so you can inspect the raw traffic and keep stronger evidence of what your API testing sent and received.