workerd "Response constructor: invalid redirect value" on 301 redirect

TL;DR

Response.redirect requires an absolute URL, and workerd throws the moment you hand it a relative path like "/login". Browsers are lenient about this in some paths, workerd is not. Build the target with new URL(path, request.url) so it is always absolute, then redirect.

TypeError: Response constructor: invalid redirect value

Steps

1. Find the throwing redirect call. Search your worker for Response.redirect:

grep -rn "Response.redirect" src

Expected: one or more call sites; the throwing one passes a relative path or a malformed string.

2. Make the target absolute using the incoming request as the base:

const url = new URL("/login", request.url);
return Response.redirect(url.toString(), 301);

Expected: no relative paths reach Response.redirect anywhere in the handler.

3. Confirm the status code is a real redirect status: 301, 302, 303, 307, or 308. Anything else with a Location header trips the same validation.

Expected: the status is one of those five.

4. Test locally and check the response:

wrangler dev

Then request the redirecting route and confirm you get a 301 with a correct absolute Location header. Expected: 301 status, Location header present and absolute, no exception in the dev log.

Use this when

• Workerd throws "Response constructor: invalid redirect value" on a redirect
• A redirect that works in the browser throws inside the worker
• You are constructing redirect targets from user input or route params

Not for this skill when

• The redirect returns but points at the wrong place; that is a logic bug, not this error
• The error comes from a framework helper rather than a direct Response.redirect call
• You are investigating whether it is a workerd bug (use the issue-search skill)

Variant phrasings

• TypeError invalid redirect value workerd
• Response.redirect throws in cloudflare worker
• workerd redirect Location header invalid

Why it happens

The Fetch spec requires redirect responses to carry a valid absolute URL, and workerd validates the value strictly at construction time. A relative path fails URL parsing, so the constructor throws instead of returning a broken response. Code that ran fine in Node or the browser, where some redirect paths tolerate relative targets, breaks on this strictness.

Edge cases

• Redirect targets built from user input can contain spaces or unicode; encode them before constructing the URL or the parse fails the same way.
• In tests, request.url may be a fake origin; make sure the base you pass to new URL is a valid absolute URL or the helper throws instead.
• 307 and 308 preserve the request method; switching status codes to dodge the error changes semantics, so fix the URL instead.
• Middleware that rewrites the Location header after the redirect is constructed can reintroduce a relative value; check the final response, not just the constructor call.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_phKUC2mdzWzmm2opWau0zg