Vercel MCP endless auth loop

Help
1

I’m experiencing an endless authentication loop when trying to use the Vercel MCP with Claude Code. This is happening on two separate machines, so I’ve ruled out local environment issues.

What I’ve tried:

  • Revoked and regenerated all Vercel access tokens

  • Fresh setup on a second machine

  • General troubleshooting (clearing caches, reinstalling, etc.)

Behavior: The MCP initiates auth but never completes — it just loops back to the auth prompt indefinitely. No specific error code is shown.

Environment:

  • Claude Code (latest)

  • Vercel MCP

  • Issue reproduces across multiple machines

Has anyone else run into this or found a workaround? Any help appreciated.

3

Hi @community-backoffice, thanks for reaching out. I’m the community’s system bot.

Sorry to hear you’re experiencing this endless authentication loop - I understand how frustrating that must be, especially since you’ve already tried multiple troubleshooting approaches across different machines.

You’ve provided good detail about what you’ve tried. To help investigate this further, could you share:

  • The exact steps you’re taking when setting up the Vercel MCP with Claude Code
  • Any console logs or error output that might appear during the auth process (even if no specific error code is shown)
  • Which version of the Vercel MCP you’re using
  • Whether this started happening recently or if it’s been an issue from the first time you tried to set it up

This additional context will help the team understand what’s happening with the authentication flow.

4

Same issue @coppinger , did you manage to solve it?

6

This pattern (auth starts, “succeeds” in browser, then Claude immediately asks to auth again) is almost always the auth “completion” signal never making it back to the MCP process. So it falls back to “not authenticated” and restarts.

  • Browser callback/cookies not sticking: the flow relies on a browser session or a loopback callback, but cookies/redirects/loopback are blocked (privacy tools, hardened browser settings, OS “open in external browser” behavior, or corporate security software).
  • SSO / org restrictions: Vercel teams with SAML/SCIM or tightened security can allow login but block token issuance/usage in a way the MCP doesn’t surface cleanly (so it just re-prompts).
  • Network/proxy/SSL inspection: the OAuth completion redirect or token exchange is being intercepted/rewritten.
  • Clock skew: if either machine’s clock is off, state/PKCE validation can fail and look like a loop.

are you authenticating into an SSO-managed Vercel team or used vercel CL login on same network?