~/tools / MCP Config Checker
MCP Config Checker — Check an MCP config file for mistakes
Check an MCP server configuration file (.mcp.json or claude_desktop_config.json) for mistakes: a missing type, the wrong top-level key, reserved or invalid names, relative paths, unset variables and secrets written into the file. Nothing leaves your browser.
Rules checked against the documentation on 2026-10-23.
Documentation: Claude Code / Model Context Protocol / VS Code
Not checked: whether a command exists, whether a package installs, whether a remote server answers, and settings that other applications read differently.
Everything runs in your browser. The configuration is not uploaded.
MCP servers are set up in a JSON file, and a small mistake can make a server silently fail to appear. A server entry with a url but no type is skipped, a file that uses the VS Code key servers is not read by Claude Code or Claude Desktop, and an environment variable that is not set is passed on as plain text. This tool reads a configuration you paste and lists what the documentation says will not work, what is worth checking, and what is only a note. It also warns when a token seems to be written straight into the file, where it can end up in version control. The rules come from the documentation of Claude Code, the Model Context Protocol and VS Code, checked on the date shown below the tool.
Use Cases
- Finding out why an MCP server does not show up after you edit .mcp.json or claude_desktop_config.json
- Checking a configuration you copied from a README before you add it to a shared project
- Spotting tokens and passwords written into a configuration file before it is committed
Usage
- Paste the contents of your MCP configuration file, or load the example.
- Read the servers found and what kind each one is, then the list of findings. Fix means the documentation says the entry will not work, Check means it is worth a look, and Note is for information.
- Edit the file, paste it again, and restart the application that reads it.
FAQ
Which files and applications does it cover?
The mcpServers format used by the project file .mcp.json in Claude Code and by claude_desktop_config.json in Claude Desktop. Other applications may read different fields or a different top-level key, so check their own documentation. VS Code, for example, uses a top-level key named servers.
My entry has a url but no type. Why is that a problem?
Claude Code reads an entry with no type as a stdio server, so an entry that has a url but no type is a configuration error and the server is skipped. Add a type of http, sse or ws.
What happens to a variable such as ${API_KEY} that is not set?
Claude Code expands ${VAR} and ${VAR:-default} in command, args, env, url and headers. If a variable is not set and has no default, the configuration still loads, Claude Code shows a warning and uses the text ${VAR} as written. Add a default with ${VAR:-default} where that is safe.
Why does it warn about a token in the file?
A token written directly into a configuration file can be shared when the file is committed or sent to someone. The check is a heuristic based on known token formats and on names such as api-key, token and password, so it can miss a secret or flag a harmless value. Using ${VAR} keeps the value out of the file.
Does it start the server or test the connection?
No. It reads the text only. It cannot tell whether a command exists, whether a package can be installed or whether a remote server is reachable, so test the server in the application after the file passes.
Is my configuration sent to a server?
No. The check runs in your browser.