proxypin

ProxyPin is a free, open-source app for capturing and inspecting HTTP and HTTPS network traffic on your device. It works similarly to commercial tools like Charles Proxy and Fiddler, but is available at no cost and runs on Windows, Mac, Linux, Android, and iOS from a single codebase built with Flutter.

The main use case is network debugging: you can see exactly what HTTP requests your apps are sending and what responses they receive, including from encrypted HTTPS connections. ProxyPin shows the full details of each request and response, including headers and body content.

Beyond just viewing traffic, ProxyPin lets you modify it. You can redirect requests to different URLs, replace request or response content, block specific URLs from reaching the server, or use JavaScript scripts to transform requests and responses in custom ways. A request mapping feature lets you respond to a network request with a local file or script instead of contacting the remote server, which is useful for testing app behavior under different conditions. AES decryption key configuration allows automatic decryption of encrypted message bodies.

Connecting a mobile device is done by scanning a QR code from the desktop app, which sets up the proxy automatically without requiring manual WiFi configuration. Domain filtering lets you limit capture to specific hostnames so the tool does not interfere with other apps running on the same device.

Captured traffic is saved automatically for later review and can be exported and imported in HAR format, a standard file format for network logs. The app is available from GitHub releases, the iOS App Store, and Google Play.