MCP Schema Validator
Validate your MCP tool definitions, resource schemas, and server manifests against the official spec.
Last updated Mar 2026
What This Validator Checks
The validator checks your JSON against the MCP specification schemas. For Tool Definitions, it verifies the name (alphanumeric + underscore/hyphen only), description, and inputSchema structure (must be a valid JSON Schema with type "object" and properties). For Server Manifests, it checks name, version, and the structure of tools, resources, and prompts arrays. For Client Configs (Claude Desktop format), it validates the mcpServers object structure, checking that each server has either a command (for stdio transport) or a url (for SSE/HTTP transport).
Common MCP Schema Errors
- Missing inputSchema — Every MCP tool must declare its input parameters as a JSON Schema object, even if it takes no arguments (use an empty properties object).
- Invalid tool name — Tool names must contain only letters, numbers, underscores, and hyphens. Spaces, dots, and special characters are not allowed.
- npx without -y flag — When using npx to run an MCP server in Claude Desktop config, omitting the -y flag can cause an interactive confirmation prompt that blocks the server from starting.
- Missing required fields — The validator identifies which required fields are missing and where in the JSON structure they should appear.
Auto-Detection
In auto-detect mode, the validator examines key fields in your JSON to determine the schema type: if it contains mcpServers, it is treated as a client config; if it contains inputSchema, it is treated as a tool definition; if it contains name and version, it is treated as a server manifest. You can override the detection by selecting a specific schema type.