MCP Configuration JSON Checker
Check JSON syntax, command/args/env structure and Windows path escaping in Claude Desktop local stdio settings without executing anything.
Input
The fictional example is never executed.
Result
Run immediately with the editable example.
Supported syntax and processing
Check JSON syntax and key value types for local stdio servers in Claude Desktop settings. The tool does not run commands, install packages, connect to servers or transmit secret values.
Under mcpServers, command must be a nonempty string; optional args is a string array and optional env an object of string values. Duplicate JSON keys and reserved prototype keys are rejected. Backslashes in Windows paths must be doubled in JSON. Control characters in command are errors; path-like control characters in args trigger only a review notice.
Input example
The public example has 1 local server, 1 args string and 1 env string value. The result shows these counts and the scope; it never runs node or server.js. Changing an env value to a number produces a string-value error.
Supported range and boundaries
Supports 50,000 JSON characters and 1–50 servers. Per server: command up to 2,048 characters, args up to 200 strings of 2,048 characters, and env up to 100 values of 8,192 characters. Server fields beyond command/args/env are outside scope. Other top-level app settings are counted but unchecked. VS Code, Cursor, remote HTTP settings, file existence, command safety, permissions and connection success are not verified.
Inputs and results stay in your browser. They are not saved or put in URLs or analytics. Leaving or refreshing the page restores the public example.
Frequently Asked Questions
Does this check VS Code or Cursor settings?
Only the basic Claude Desktop mcpServers local stdio format is supported. Other clients' servers keys and remote URL settings are reported as unsupported, not as universally invalid.
Does a passing result mean the server will connect safely?
No. Only static types such as strings and arrays are checked. Verify paths, execution permissions, dependencies, package trust and server responses separately. This tool neither installs nor executes the configuration.
Are API keys or command contents repeated in results?
Results show counts and generic guidance instead of server names, commands, arguments or environment values. Inputs stay in the browser and are not saved. Reset, refresh and navigation restore the public example.
Calculation criteria and reference materials
- MCP Documentation — Local Servers in Claude Desktop
Reference for Claude Desktop mcpServers, command, args, env and Windows JSON path notation. This tool does not execute, install or connect.
Verification of calculation criteria: · Calculation·verification principles · Report errors