Fiddler
Fiddler is a web debugging proxy tool, similar in purpose to Charles Proxy, that captures and inspects HTTP/HTTPS traffic between a client and server — widely used on Windows for API debugging, performance analysis, and simulating network conditions during testing.
Like Charles Proxy, Fiddler sits between the application and the network, logging every request and response for inspection — testers use it to verify API calls are correctly formed, debug unexpected responses, and replay or modify captured requests to test edge cases without changing application code.
It's historically been the more common choice on Windows specifically, with Charles favored more often on macOS, though both tools now support cross-platform use — the choice between them in practice usually comes down to team familiarity and platform preference rather than a meaningful capability gap.
