What Is Oproxy?
Oproxy is a browser-native network proxy tool that lets you inspect and modify HTTP and WebSocket traffic without any external proxy setup. You install it as a browser extension, open the devtools panel, and you're immediately looking at every request and response flowing through your tab.
The killer feature: you can rewrite requests and responses on the fly. Change headers, mutate body payloads, stub API responses, delay network calls for testing — all from a clean UI inside Chrome or Firefox.
Why This Matters for Builders
The traditional approach to intercepting traffic involves setting up a local proxy like mitmproxy, installing a root CA, trusting it system-wide, and dealing with certificate warnings on every domain. It's powerful but painful.
Oproxy cuts that workflow down to seconds. For developers working on:
- Frontend-backend contract testing — stub a buggy API endpoint and verify your UI handles it correctly.
- Debugging WebSocket connections — see every frame, edit it, resend it.
- Testing edge cases — simulate slow responses, HTTP errors, malformed payloads without touching the server.
How It Works
Oproxy runs entirely in the browser. It registers as a service worker or background script that intercepts fetch and WebSocket calls at the platform level. The devtools panel exposes a request list, a detail view, and a rules engine.
Rules can be scoped by URL pattern, method, or header value. You can define them as:
- Block — drop matching requests silently.
- Delay — inject artificial latency.
- Rewrite — replace response body, status, or headers.
- Passthrough — log without modifying.
The Developer Experience
The UI is straightforward: a request table with method, URL, status, and timing columns, a detail pane that shows headers and body, and a rule editor with regex support. There's also a console-like log view for WebSocket frames.
Because it runs in-browser, there's no network hop to a proxy server. Latency between your code and the tool is essentially zero. For high-frequency debugging or performance-sensitive testing, this matters.
Open Source and Extensible
Oproxy is MIT-licensed and lives on GitHub. The extension architecture is designed to be extensible — you can add custom rule types, custom reporters, or integrate with external services via a simple plugin API.
If you've been tolerating mitmproxy's ceremony or paying for tools like Charles, Oproxy is worth a look. It's free, runs in your browser, and ships with the features most developers actually need.
Get Started
Find Oproxy on GitHub and install the browser extension. The project includes a quick-start guide for common use cases like API stubbing and WebSocket debugging.
*Have a tool or project you'd like to see covered? Drop it in the comments or reach out.*