What is API?
API (Application Programming Interface) is a computing interface that defines how software components interact with each other. It is a way of programmatically interacting with a separate software component or resource and expose functionality for internal or external use and testing. API defines what requests can be made, how they will be made and hides complexity from developers. API extends systems to partners, organizes code, and makes components reusable.

What is API testing?
API testing is a set of quality assurance actions that include making calls to an API endpoint, getting API responses, and validating API status codes, response times, and data against predefined rules. API testing is usually performed by a software tool or web service and mainly focuses on testing the business logic layer.

Why is API Testing Important?
API testing determines whether the API meets expectations for functionality, reliability, performance, and security. API testing is essential for the entire development, implementation and maintenance of APIs. API testing is necessary to accompany the API to make it functional and ready for its purpose.

How do I Test API Online?
You can test API online by composing and executing various API requests right from your browser. To test API online:
1. Enter the URL of the API endpoint and select the appropriate HTTP method.
2. In the Content tab, enter the data you want to send to the API endpoint.
3. If your API server requires authorization, enter your credentials in the Authorization tab.
4. Click Send to submit your API request, check the returned API status code, response time, and content.
5. Re-run the API tests by changing the API endpoint URL, HTTP method, and request data.


Test API with Online REST API Client
Calqlt is the most popular Online REST API testing tool. You can quickly and easily test your API by sending API requests to REST API endpoints directly from your browser. Calqlt API Tester provides millisecond accurate timings for API requests and server responses. With the Calqlt load testing tool, you can test the API against hundreds of simulated concurrent users from different geographic regions. The REST API client works right in your browser. No coding. No desktop app. Fully online.

JSON and XML API Tester
Easily inspect returned JSON and XML responses. The built-in JSON and XML formatters automatically format and validate the returned data and highlight any errors in JSON and XML.

REST API Examples
Learn REST API best practices by browsing a collection of real-world REST API examples.