fix(wrangler): don't proxy localhost requests during dev

[edmundhung]

Fixes #8906.

It looks like wrangler's proxy setup bleeds into miniflare's inspector proxy and should skip proxying requests to localhost. I considered scoping the proxy setup to the wrangler CLI only , but the Vite plugin also needs it for remote binding API calls.

This fix replaces ProxyAgent with undici's EnvHttpProxyAgent, which natively supports NO_PROXY. When NO_PROXY is not set, it defaults to localhost,127.0.0.1,::1, so local dev server requests are never proxied.

The NO_PROXY config only applies to the request destination, not the proxy server address. So a proxy running on localhost (e.g., HTTP_PROXY=http://127.0.0.1:11451) still works for outbound API calls.

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• Tests
  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows:
    1. Run vite dev with a non existent HTTP_PROXY (e.g. http_proxy=http://127.0.0.1:11451 vite dev)
    2. See if you can reproduce the same error (i.e. TypeError: fetch failed)
    3. Update vite plugin to the pre-release version and try again
  • Additional testing not necessary because:
• Public documentation
  • Cloudflare docs PR(s):
  • Documentation not necessary because: bugfix

A picture of a cute animal (not mandatory, but encouraged)

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[changeset-bot]

🦋 Changeset detected

Latest commit: 88594ca

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[claude]

Claude finished @edmundhung's task —— View job

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Changeset Review

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✅ All changesets look good

The changeset .changeset/fix-proxy-localhost.md is well-written and follows all guidelines:

• ✅ Version Type: patch is correct for a bug fix
• ✅ Changelog Quality: Clear, detailed description with proper context about the problem and solution
• ✅ Markdown Headers: No h1/h2/h3 headers used
• ✅ Format: Follows the recommended TITLE + BODY structure with imperative title
• ✅ Content: Explains both the bug and the fix, includes technical details about EnvHttpProxyAgent and NO_PROXY behavior

The changeset effectively communicates what was broken, how it's fixed, and important details about the new behavior.

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wrangler

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commit: 88594ca

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.

[jamesopstad]

Does this mean that proxy environment variables now work, or just that they don't crash?

[edmundhung]

Does this mean that proxy environment variables now work, or just that they don't crash?

It should work. Just skip the proxy when a request is made against localhost.

[devin-ai-integration]

Devin Review found 1 new potential issue.

View 7 additional findings in Devin Review.