FiddlerCore

What FiddlerCore is

FiddlerCore is a .NET class library for embedding HTTP and HTTPS traffic capture and modification in .NET applications without the Fiddler user interface. It supports content filtering, storing and reloading traffic, and importing or exporting traffic in various formats. Developers can replace frontend or backend services, replicate APIs, modify responses, and simulate network conditions or user loads for testing. The product also describes monitoring network systems, devices, and applications to find delays, missing services, or potential dangers. Documentation says it supports virtually any client application and most devices through mobile proxy settings. Listed capabilities include request and response editing, traffic replay, response mocking, WebSocket inspection, and proxy chaining. Integration is listed for Telerik Fiddler and Telerik TestStudio. The latest version targets .NET Standard 2.1; .NET Framework 4.8 requires FiddlerCore 5.0.2 or older because 6.x is incompatible. It runs on Windows, macOS, and Linux. Internal Applications Use costs $2,999 a year per application. A 30-day trial excludes end-product integration and commercial, productive, training, or redistribution use.