I asked what a proxy was. Now I am writing about it. Here are the mistakes that cost me the most time, so they do not cost you yours.
Save yourself an hour
Match the request URL, not the page URL.
Turn rules off when you are done.
Reload after a change, and check you are on the right tab.
Mistake 1: matching the page URL instead of the request URL
Rules match the URL the page requests, like https://api.example.com/users, not the address in the address bar. Open the Network tab, copy the request URL, and build the pattern from that.
Mistake 2: forgetting a rule is still on
A mock that answers forever will confuse you tomorrow when the real API changes and nothing on screen does. Give rules clear names and switch them off, or group them so one toggle turns them all off.
Mistake 3: fighting the cache
If the response looks unchanged, the browser may be serving a cached copy. Reload with cache disabled in DevTools while you experiment.
My rule is perfect
🧊
The cache: no
Hard reload. Always hard reload.
Mistake 4: testing the wrong environment
Check that the rule targets the environment you are testing (staging vs production URLs).
Check that the extension is enabled for that tab.
Prefer a wildcard pattern over an exact URL when query strings vary.
Please be gentle. I am the intern. I have made all of these and will make one more tomorrow.
Arnav is the intern, and the voice for anyone meeting API debugging for the first time. He writes what he wishes someone had explained on day one: plain language, small steps and the occasional meme when a status code deserves one. Expect honest questions, no gatekeeping and a lot of learning in public.
Five short exercises that take you from "what is a proxy interceptor?" to mocking, deep-merging, failing and redirecting real API calls, with copy-paste rules.