Claude Code / AI Coding Tools
Bug: Gmail MCP integration uses wrong OAuth client — cannot grant Gmail permissions
Fix OAuth scope routing so Gmail MCP uses correct Gmail OAuth client to grant mail.google.com permissions Includes evidence for Claude Code troubleshooting demand.
- Category
- AI Coding Tools
- Error signature
built-in Gmail MCP server routes through Google Drive OAuth client instead of Gmail-specific client; Google consent shows Drive scopes only, Gmail calls fail with 403 Forbidden- Quick fix
- Verify the account session, API key, provider settings, and environment where the failing tool is running.
- Updated
What this error means
built-in Gmail MCP server routes through Google Drive OAuth client instead of Gmail-specific client; Google consent shows Drive scopes only, Gmail calls fail with 403 Forbidden is a Claude Code failure pattern reported for developers trying to fix oauth scope routing so gmail mcp uses correct gmail oauth client to grant mail.google.com permissions. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.
Why this happens
GitHub Issue #51326 (anthropics/claude-code), created 2026-04-20, 2 comments. Real bug where built-in Gmail MCP is unusable because it authenticates via ‘Claude for Google Drive’ client. Distinct from other MCP auth issues — this is about wrong OAuth client mapping, not browser launch. Category: Claude Code = AI Coding Tools.
Common causes
- GitHub Issue #51326 (anthropics/claude-code), created 2026-04-20, 2 comments. Real bug where built-in Gmail MCP is unusable because it authenticates via ‘Claude for Google Drive’ client. Distinct from other MCP auth issues — this is about wrong OAuth client mapping, not browser launch. Category: Claude Code = AI Coding Tools.
Quick fixes
- Confirm the exact error signature matches
built-in Gmail MCP server routes through Google Drive OAuth client instead of Gmail-specific client; Google consent shows Drive scopes only, Gmail calls fail with 403 Forbidden. - 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.
Sources checked
Evidence note: GitHub Issue #51326 (anthropics/claude-code), created 2026-04-20, 2 comments. Real bug where built-in Gmail MCP is unusable because it authenticates via ‘Claude for Google Drive’ client. Distinct from other MCP auth issues — this is about wrong OAuth client mapping, not browser launch. Category: Claude Code = AI Coding Tools.
Related errors
- AI Coding Tools
FAQ
What should I check first?
Start with the exact built-in Gmail MCP server routes through Google Drive OAuth client instead of Gmail-specific client; Google consent shows Drive scopes only, Gmail calls fail with 403 Forbidden 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 built-in Gmail MCP server routes through Google Drive OAuth client instead of Gmail-specific client; Google consent shows Drive scopes only, Gmail calls fail with 403 Forbidden.