Troubleshooting

A rule is not hitting, headers are not applied, a redirect loops — the usual causes and fixes.

The rule does not hit

Check	Fix
Global switch off	Turn it on in the popup or the panel top bar
Project disabled	Enable the project in the sidebar
Rule disabled or dimmed	Hover the rule — the tooltip names the reason (quota, plan)
An earlier rule wins	Rules match in order and the first enabled hit wins — move the specific rule above the broad one
Wrong method	A rule set to `GET` never matches a `POST`; use `ALL` if you are unsure
Path vs full URL	`Exact` compares the whole string — use `Contains` or `Path params` for dynamic paths
Query string in the pattern	`Contains /api/users` matches `?page=2` too; `Exact` does not
Conditions too strict	All conditions must match — check header casing and body dot paths
Already-loaded data	The page cached the response — hard reload (⇧⌘R) or clear the app cache

It worked before, now it does not

Service worker cache — a PWA can serve the response itself; unregister it in DevTools → Application.
Chrome’s own overrides — check DevTools → Network → Overrides; two tools answering the same request is confusing but harmless.
Extension reloaded — after an update, already-open tabs stop seeing the injected script until reloaded.

Headers or Redirect do nothing

The rule is marked Inactive — the tooltip gives the compile reason (invalid regex, protected header, empty target, unsupported method).
The request never reaches the browser’s network request layer — a page service worker or an in-memory cache answered it. Use Mock for those.
The redirect target is an http address from an https page — the browser blocks it except for localhost.
A CORS error appeared after the redirect — add a Headers rule with the CORS preset, and remember cookies follow the target domain.

The page reloads forever

Two redirect rules pointing at each other, or a substitution that keeps growing the URL, form an endless loop. The panel flags the chain on the rule before it bites. Disable one rule in the chain, or make the target resolve to the current URL — the browser skips a redirect that changes nothing.

A JS Hook fails

Message	Cause
`import()` always fails	The sandbox CSP only allows the extension’s own files — use `context.loadScript(url)` with a UMD build
ES module cannot run	Pass an IIFE / UMD build (`*.min.js`), not an ESM bundle
`req is not defined`	Hooks take a single `context` argument — use `context.req` / `context.res`
Execution timed out	The hook never returned or awaited forever — add a timeout or simplify the code

Storage and quota

“Could not save your rules” — the 10 MB extension storage is full. Export a backup, then delete unused rules, large bodies or long JS hooks.
“N not taking effect” — you are over the Free quota. Disable or delete rules, or upgrade.
Import was trimmed — the report after the import lists what was dropped; split the file and import in parts.

Still stuck

Email support with the rule exported (panel → Export), the page URL pattern, the expected and actual response, and your Chrome version. Do not paste cookies, tokens or customer data — redact them first.

Stuck, or need something clarified? support@mockrew.com·Terms of Service