Implementation guide
Troubleshooting MCP authentication errors
A 401 response usually indicates missing, malformed, expired, or invalid credentials. A 403 usually means the credential was recognized but is not permitted to call the selected API operation.
Fast checks
Compare the generated client configuration with the API security scheme.
- Verify the exact header and environment-variable names
- Include the Bearer prefix when required
- Replace expired or revoked credentials
- Confirm roles, scopes, and operation permissions
Correlate evidence
0mcp and upstream logs answer different parts of the failure.
- Find the failed tool call by timestamp
- Review its safe status and timing metadata
- Match it to the upstream API log
- Reconnect the client after changing its secret configuration
For complete product instructions, read the 0mcp documentation. Protocol reference: Model Context Protocol specification.
Published and last reviewed: July 13, 2026