Claude Code / AI Coding Tools

Claude Code MCP server auth returns HTTP 431 error on Linux

Fix Claude Code MCP server authentication returning HTTP 431 error on Linux platform Includes evidence for Claude Code troubleshooting demand.

Source-backed Last updated May 17, 2026 1 source Needs local verification

Category: AI Coding Tools
Error signature: HTTP ERROR 431 — MCP server authentication failure (browser restart!)
Quick fix: Verify the account session, API key, provider settings, and environment where the failing tool is running.
Updated: May 17, 2026
Verification status: Source-backed
Evidence: 1 public source URL

Before you change production

This page includes public source URLs in the imported troubleshooting record. Compare those references with your version and environment before applying changes.

Reproduce the smallest failing action and save non-secret logs before changing configuration.
Check versions for Claude Code, related SDKs, package managers, CI runners, and hosting providers.
Change one setting or dependency at a time, then rerun the same failing command or request.
Avoid destructive commands, credential rotation, billing changes, or security relaxations without a rollback plan.

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

Confirm the exact error signature matches HTTP ERROR 431 — MCP server authentication failure (browser restart!).
Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
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

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

Diagnostic flow for this page

Match HTTP ERROR 431 — MCP server authentication failure (browser restart!) exactly before applying the quick fix.
Compare the failing environment with Claude Code versions, account scope, provider settings, and deployment context.
Check the listed common causes in order, starting with the cause that best matches your logs.
Use the evidence status below to decide whether to confirm against public sources or official documentation.
Apply one reversible change, rerun the smallest failing action, and keep rollback notes.

FAQ

What does HTTP ERROR 431 — MCP server authentication failure (browser restart!) mean in Claude Code?

HTTP ERROR 431 — MCP server authentication failure (browser restart!) indicates the workflow described by "Claude Code MCP server auth returns HTTP 431 error on Linux" failed in a AI Coding Tools context. Start by confirming the exact signature and the component that emitted it.

What should I check first for HTTP ERROR 431 — MCP server authentication failure (browser restart!)?

Check whether this cause matches your environment: 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.

Is the HTTP ERROR 431 — MCP server authentication failure (browser restart!) guidance source-backed?

The "Claude Code MCP server auth returns HTTP 431 error on Linux" page is labeled source-backed. It has 1 public source URL from github.com, so use that evidence status when deciding how much additional verification you need.

When should I avoid the quick fix for HTTP ERROR 431 — MCP server authentication failure (browser restart!)?

For "Claude Code MCP server auth returns HTTP 431 error on Linux", avoid applying "Verify the account session, API key, provider settings, and environment where the failing tool is running." when the error text differs, the affected version or provider is different, or the change would touch credentials, billing, DNS, production deploy settings, or irreversible data.

What should I collect before debugging HTTP ERROR 431 — MCP server authentication failure (browser restart!)?

For "Claude Code MCP server auth returns HTTP 431 error on Linux", collect the failing Claude Code command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.