Claude Code MCP server auth returns HTTP 431 error on Linux

What this error means

HTTP ERROR 431 — MCP server authentication failure (browser restart!) is a Claude Code failure pattern reported for developers trying to fix claude code mcp server authentication returning http 431 error on linux platform. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Found in anthropics/claude-code repo issue #58951 (created 2026-05-14). OAuth flow broken with HTTP 431 header too large error. Version-specific regression in v2.1.141 on Linux x64. Category: AI Coding Tools.

Common causes

• Found in anthropics/claude-code repo issue #58951 (created 2026-05-14). OAuth flow broken with HTTP 431 header too large error. Version-specific regression in v2.1.141 on Linux x64. Category: AI Coding Tools.

Quick fixes

1. Confirm the exact error signature matches HTTP ERROR 431 — MCP server authentication failure (browser restart!).
2. Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
3. Verify the account session, API key, provider settings, and environment where the failing tool is running.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/anthropics/claude-code/issues/58951

Evidence note: Found in anthropics/claude-code repo issue #58951 (created 2026-05-14). OAuth flow broken with HTTP 431 header too large error. Version-specific regression in v2.1.141 on Linux x64. Category: AI Coding Tools.

Related errors

• AI Coding Tools

FAQ

What should I check first?

Start with the exact HTTP ERROR 431 — MCP server authentication failure (browser restart!) text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Claude Code workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without HTTP ERROR 431 — MCP server authentication failure (browser restart!).