If an MCP server is missing, disconnected, or connected with no tools, first identify which stage is failing: client configuration, approval or authentication, transport or process startup, or tool discovery. Codex and Claude Code expose different status and log surfaces, so follow the checks for the client you are using. A server appearing in a list is not proof that it returned tools or that a tool call works.
Start by identifying what is failing
Record the client and version, transport, configuration scope, server URL or launch command, exact status, and error text. Classify the symptom before changing settings:
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- Absent: the client may not be reading the configuration or the server may be disabled or rejected.
- Present but disconnected or awaiting action: investigate transport, startup, authentication, or approval according to the displayed status.
- Connected with zero tools: the connection may have succeeded while tool-list discovery failed.
- Tools visible but calls fail: inspect the tool execution error, server behavior, and tool metadata or schema.
These are separate stages. OpenAI describes tool listing as a discovery step; MCP failures can surface as protocol, execution, or connectivity errors. OpenAI’s MCP server guide
Why are my MCP tools not showing up in Codex?
Use this sequence to distinguish a server that is not reachable from one that connects but does not advertise usable tools. OpenAI’s plugin troubleshooting guidance says its server, tool, and discovery checks also apply to Codex. OpenAI plugin troubleshooting
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Confirm the server and endpoint
- Check that the server process is running and that the configured URL points to the current host and port.
- For the documented plugin troubleshooting case, verify that the endpoint is
/mcp. If the port changed, update the configured URL. - Check reachability from the environment that actually makes the connection; a URL accessible from your laptop may not be reachable from a service or execution environment.
Check startup and execution context
For the OpenAI Agents API connection path, establish whether the connection runs from the service or from an execution environment. Environment-origin HTTP and stdio connections require an environment. For stdio, verify that the configured executable and its dependencies exist in that environment. If an inline stdio configuration specifies cwd, it must be an existing absolute path. OpenAI Agents API MCP connections
Verify credentials and headers
Check that the server expects the credential type you configured, that required token or header values are present, and that the credential is associated with the correct server URL. Do not paste tokens into shared logs or support requests.
Inspect the discovery result and logs
If the server is reachable but no tools appear, check whether its tool-list handler returns tools and whether the returned metadata and schemas are valid. OpenAI’s guide identifies a successful listing as an mcp_list_tools item; a visible connection alone does not establish that discovery succeeded. If a tool is listed but fails when called, use the failed-turn detail to distinguish protocol, execution, and connectivity errors.
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For the Agents API path, inspect the failed turn detail and, for stdio, the MCP process logs. These help separate a launch failure from a server response or tool-call failure. OpenAI’s MCP server guide
How do I check whether my MCP server is connected in Claude Code?
Claude Code has command-line and in-session status surfaces. Run these from the relevant project or configuration context:
claude mcp list— review the configured servers and their reported status.claude mcp get <name>— inspect the entry for the server in question.- In an interactive Claude Code session, run
/mcp— check its connection state and displayed tool count.
Read the exact state before changing configuration. A pending approval or authentication-needed state is not the same as a failed connection; disabled or rejected configuration is not necessarily a network outage. Status labels and caching behavior can change between Claude Code versions, so consult the current Claude Code MCP documentation and the documentation for your installed version.
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Check configuration location and approval
Confirm that the server is configured in the intended scope and that Claude Code is reading that configuration. Project-level configuration can require approval; a rejected or disabled entry needs its configuration state addressed. The Claude Code FAQ describes project-root .mcp.json and claude mcp add as configuration routes. After adding a server, restart Claude Code and check /mcp to verify its status rather than assuming that writing the configuration connected it. Claude Code user FAQ
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A connected state with a zero tool count means the server started and the connection is reported as established, but it does not prove that the server returned a usable tool list. Investigate discovery separately from transport.
Check the server’s tool-list response
- Confirm that the server implements and returns its tool list, rather than only accepting a connection.
- Inspect server stderr and the tool-list handler for errors or invalid metadata.
- Check Claude Code’s MCP debug output for the discovery request and response.
Claude Code’s configuration-debugging guidance identifies a connected server with zero tools as a case where the server has started but is not returning a tool list. It also recommends examining debug output. Claude Code configuration debugging
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Check configuration and process environment
If the server is absent rather than connected with zero tools, verify its configuration location and scope. If it starts but behaves differently than expected, check whether its launch environment contains the variables it needs. Preserve the exact status, tool count, and relevant debug output when investigating; redact tokens and other secrets.
How do I troubleshoot an MCP authentication or connection error?
Use the client’s reported state and logs to decide which layer to test. Repeatedly restarting a healthy process will not fix a missing credential, unreachable endpoint, rejected configuration, or failing tool-list handler.
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|---|---|---|
| Server absent from the client | Configuration scope, location, or disabled/rejected state | Inspect the client’s configuration and status surfaces; in Claude Code, use claude mcp list and claude mcp get <name>. |
| Connection failure or startup error | Transport reachability, URL, executable, dependencies, or process environment | Test from the actual connection environment; for stdio, confirm the executable and dependencies are present and any cwd is an existing absolute path. |
| Authentication-needed or pending approval | Credential or approval state | Follow the client’s status-specific action; verify credential type, token/header presence, endpoint association, and project approval where applicable. |
| Connected, zero tools | Tool-list discovery or server handler | Inspect the server’s response, tool metadata, stderr, and client debug output. |
| Tool appears, call fails | Tool execution, protocol, schema, or connectivity | Inspect the failed call or turn detail and compare the advertised tool schema with the server’s behavior. |
For Codex and the documented OpenAI Agents API path, use the failed-turn details and stdio process logs. For Claude Code, use the status commands, /mcp, and documented debug output. Keep the client version, exact error, server endpoint or command, transport, and relevant logs together so the failing stage remains clear.
What confirms that the problem is fixed?
Configuration being saved or a server appearing in a list is not enough. Confirm that the client reports a successful connection, a nonzero tool count when tools are expected, and a successful call to an available tool. If the connection succeeds but discovery still fails, keep investigating the server’s tool-list handler rather than treating the connection status as proof of recovery.
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