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MCP / Tool routing

MCP tools not available in session

The agent expected a tool, but the MCP server was not connected, filtered, or registered for this session.

Error text / 报错原文

  • MCP tools not available in session
  • tool not found
  • No tools available

What it means

The agent expected a tool, but the MCP server was not connected, filtered, or registered for this session.

Most common causes

  • Server startup timeout
  • Tool list changed after session start
  • Client filtered tools by trust policy
  • Workspace-specific MCP config was not loaded

Fastest fix

  • Reproduce the smallest failing case outside the agent.
  • Confirm auth, session, and transport before changing app code.
  • Disable unrelated tools or servers and retry once.
  • Capture the exact timestamp, client version, and raw error text.

Safe fix

  • Keep secrets in environment variables or the platform secret store.
  • Use least-privilege scopes and read-only tools by default.
  • Add validation around manifests, schemas, and callback URLs.
  • Document the working local and production configuration.

What not to do

  • Do not paste OAuth tokens or session IDs into public logs.
  • Do not bypass TLS, CSP, or permission prompts as a permanent fix.
  • Do not enable every MCP tool globally just to make one task pass.

Diagnostic commands

node --version
curl -I "$MCP_SERVER_URL"
echo "$OAUTH_CLIENT_ID"

Related tools

Related errors

Sources