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.
• Client-specific remote transports. Claude Code treats a server with a urlbut no type as stdio, which is a config error. Use type: "http" for a remote HTTP server. The client picker switches this rule for Claude Desktop and VS Code or Cursor.
• 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.
• Environment references. Claude Code supports environment-variable expansion. Claude Desktop does not expand the same placeholders, while VS Code and Cursor use their own variable syntax. Pick your client before taking a warning as an instruction.
• 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.

Claude Code quick check

After fixing the shape, run claude mcp listto confirm registration and /mcp in a Claude Code session to inspect connection status. Project-scoped configuration belongs in a.mcp.json file at the project root and needs approval when Claude Code finds it. Checked against Anthropic's Claude Code MCP docs on September 9, 2026.

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.