“Error Executing MCP Tool: Not Connected” means your AI client does not currently have a usable connection to the selected Model Context Protocol (MCP) server. It does not, by itself, prove that the server is stopped. A process can print that it is running on stdio while the client has not completed initialization, or has disconnected after startup. Work through the client status, logs, launch configuration, transport, and handshake in that order.
What the error actually tells you
MCP is an open standard that lets an AI application use tools and data supplied by an MCP server. The client launches or contacts the server, negotiates capabilities, and then invokes tools. “Not connected” is a state symptom: the client cannot use a working connection to the server it selected.
The message is not a diagnosis. Reports have appeared with GitHub, Sequential Thinking, and Context7 servers, and with Cline and Roo Code on both Windows and macOS. In several reports, the server printed a normal-looking “running on stdio” message while the host still could not call any tools. Process presence and a startup line therefore are useful observations, not proof of a completed MCP handshake.
Fix it in this order
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Confirm the intended server is enabled
Open your AI client’s MCP or integrations settings. Select the exact server entry you intend to use and check that it is enabled and marked connected. Remove ambiguity between duplicate entries with similar names. If the client offers Retry Connection or Reconnect, use it once and then check the status again. Roo Code users have reported that enabling a disabled server or retrying restored access in one case; a Cline report describes a retry timing out, so this is a check, not a guaranteed repair.
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Read the client log and startup output together
Open the host’s MCP log panel, developer log, or diagnostic folder and reproduce the error once. Record:
- the exact command and arguments the client launched;
- exit code or termination signal;
- standard error output;
- whether the process stayed alive; and
- the point at which initialization or tool discovery failed.
A server that exits immediately, writes an exception to stderr, or never reaches initialization needs a launch/configuration fix. A process that remains alive but is listed as disconnected points toward transport, protocol, or handshake problems.
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Validate the launch configuration from the client’s environment
Compare the server instructions with the values saved in the client. Check the executable path, package name, arguments, environment variables, working directory, and runtime version. “It works in my terminal” is not sufficient: GUI clients may have a different PATH, home directory, permissions, shell, or current directory.
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On Windows, verify that the configured Node or other runtime is installed for the account running the client and that quoting is correct. On macOS and Linux, check executable permissions and whether the client can see the same runtime path as your shell. If a token is required, confirm that the variable is present in the client’s configuration rather than only in an interactive shell.
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Check package names and versions
Use the package name shown in the server’s own installation instructions. A Sequential Thinking issue includes a package-name correction and a version-pinning workaround in comments, but those are user-specific reports rather than universal remedies. Change a package name or pin a version only when your log identifies that package or release as the failing component; record the original value so you can revert it.
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Check transport and initialization
Both sides must support the same transport. For a stdio server, the client must launch the process and communicate over its standard input and output; diagnostic text on stdout can corrupt that protocol. Ensure the server writes human-readable logs to stderr when its documentation requires it. The GitHub server issue lists stdio compatibility and the initialization handshake as investigation targets. They are important checks, but that report does not establish either as the universal cause.
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If the client expects a network endpoint, confirm the URL, port, authentication, and TLS settings instead of configuring it as a local stdio command. Conversely, do not add an HTTP URL to a server documented only for stdio.
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Reconnect once, then capture a reproducible failure
After correcting one setting, restart the client and server, reconnect once, and invoke a simple tool. If it still fails, save the client and server versions, operating system, complete launch entry with secrets removed, exit status, and relevant log lines. This evidence is more useful than repeatedly clicking Retry and helps you search the exact client/server combination’s documentation or issue tracker.
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Why “running” can still mean “not connected”
An MCP server generally has to survive launch, speak the configured transport, answer initialization, and expose capabilities before a client can call a tool. A manual terminal test may prove only that a process started. Sequential Thinking and Context7 reports both describe successful-looking stdio startup output followed by a Cline “Not connected” state. Treat these as separate milestones:
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- Started: an executable was found and a process was created.
- Alive: the process has not exited.
- Initialized: the client and server completed the protocol handshake.
- Usable: tool discovery succeeded and a call returns a response.
Your logs should tell you which milestone is missing.
Common symptoms and targeted fixes
| Symptom | Likely area | What to check |
|---|---|---|
| Server is disabled or shows disconnected immediately | Client state | Enable the intended entry, remove duplicates, reconnect, and inspect the resulting log. |
| Process exits as soon as the client launches it | Command or runtime | Executable path, package name, arguments, runtime availability, permissions, and stderr. |
| Process remains alive but no tools appear | Transport or handshake | Stdio versus network configuration, protocol-compatible versions, clean stdout, and initialization errors. |
| Retry hangs or times out | Stale or incompatible connection | Restart both sides, then inspect logs rather than repeating retries. |
| Works in a terminal but not in the desktop client | Environment mismatch | PATH, home directory, working directory, environment variables, permissions, and shell quoting as seen by the client. |
| Token appears valid but connection still fails | Earlier connection stage | Do not stop at credential validation; verify launch, transport, and initialization. |
Windows-specific checks
- Confirm the client’s configured Node version and executable path, not just the version printed by PowerShell.
- Use fully qualified paths while diagnosing; restore variables after the connection works.
- Inspect quoting around arguments and environment values containing spaces.
- Check that security software has not terminated the child process.
A GitHub MCP report described Windows 10, Node 20.11.1, a running process, and a reportedly valid token while the client still could not connect. Those facts show why process and token checks alone cannot isolate the fault.
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- Launch the client from the same user account that owns the runtime and configuration.
- Verify execute permissions and absolute paths.
- Compare GUI-launched and shell-launched environment variables.
- Ensure shell startup files are not required to expose the runtime to a GUI application.
The Context7 report involved macOS and the same distinction between manual stdio startup and a client that remained disconnected.
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What not to conclude
- Do not assume every “Not connected” error has one root cause.
- Do not treat a startup banner as proof of a completed handshake.
- Do not claim that retrying always fixes the problem; the reports are mixed.
- Do not replace a package or pin a version without a log or server document pointing to that change.
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When to escalate
Escalate to the server maintainer or host-client issue tracker when you can provide a minimal configuration, exact versions, operating system, sanitized logs, and a repeatable failure. Mention whether the process starts, remains alive, completes initialization, and exposes tools. That separates a launch defect from a protocol or client integration defect.
Frequently Asked Questions
Will reinstalling the MCP server fix the error?
Not necessarily. Reinstallation is justified only when logs show a missing, corrupted, or incompatible package. First verify the client’s command, environment, transport, and initialization logs.
Can I test an MCP server without the AI client?
You can test whether its executable starts and remains alive, but that does not prove client compatibility or a completed MCP handshake. Use the host client’s logs for the decisive test.
Should I report the error as a server bug?
Only after checking the client entry, launch environment, transport, and handshake evidence. Include sanitized logs and versions so the maintainer can distinguish configuration from implementation failure.
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