MCP config validator

What it checks

• Duplicate server names. JSON keeps only the last of a repeated key, so adding the same server twice silently throws away your earlier edit. Nothing that validates the parsed object can see this, because by then the duplicate is gone.
• Missing or doubled transport. A server needs a command or a url. Having neither starts nothing; having both means the client picks one and ignores the other.
• Remote servers Claude Desktop drops. A server with a url and no command does not pass the Claude Desktop config schema. It is dropped, and the only warning is a generic one about invalid servers being skipped, not a message naming this server. Configure remote servers in the app instead. Other clients accept this shape. Checked against Claude Desktop 1.40609.0.
• Secrets in env. Env keys that look like tokens with a literal value. The tool names the key and never shows the value. It only looks at env, so a token sitting in headers, args, or a URL will not be flagged.
• ${VAR} references that never expand. Claude Desktop copies env values to the server as written and starts it without a shell, so a placeholder arrives as its own literal text and the server fails auth with an error that points nowhere near the config. It does not inherit your shell environment either, only HOME, LOGNAME, PATH, SHELL, TERM and USER. The one exception is ${PATH} inside PATH, which is substituted, so that is not flagged. Other clients differ: VS Code and Cursor expand ${env:VAR} and predefined variables like ${workspaceFolder} and ${userHome}. Checked against Claude Desktop 1.40609.0.
• Types and absolute paths. args that is not an array of strings, env values that are not strings, and machine-specific paths that break the moment you sync the config elsewhere.

Where your config goes

Nowhere. The validator is a plain function running in your browser. There is no upload, no request, no analytics on what you paste, and no way to link to a pre-filled version of this page. Close the tab and it is gone.