Paste your claude_desktop_config.json, hit Validate, fix the red rows before you restart Claude Desktop. Runs 100% in your browser — nothing is uploaded, nothing logged.
JSON syntax — the file must parse. A trailing comma or a JavaScript comment is the usual culprit.Top-level mcpServers object — the root must be an object with an mcpServers key holding an object of servers.At least one server — an empty mcpServers object means nothing will start.Per-server command — every server needs a non-empty command string (e.g. npx, uvx, node, python).Per-server args — args must be an array of strings when present; a missing args raises a warning since most servers need launch arguments.env object — env must be an object of string values when present. On Windows, an ENOENT referencing ${APPDATA} often means you need an expanded APPDATA entry in env.Absolute paths — directory arguments must be absolute, not relative (./data will not resolve). Relative-looking paths raise a warning.secret values pasted in env (heuristic warning — prefer input variables or an env file) and insecure http:// URLs in any URL field.~/Library/Application Support/Claude/claude_desktop_config.json, Windows at %APPDATA%\Claude\claude_desktop_config.json · logs at ~/Library/Logs/Claude/mcp*.log.