mcp-builder

MCP servers enable LLMs to call well-defined tools that connect to external services. Design involves registering tools with strict input schemas, clear annotations, and proper error handling. Both FastMCP (Python) and MCP SDK (TypeScript) provide frameworks to scaffold, validate, and run these servers with local or HTTP transports.

FastMCP is a Python framework that streamlines MCP server setup and tool registration with Pydantic validation. MCP SDK is the Node/TypeScript equivalent, using Zod for type validation. Both follow the same core patterns—server initialization, tool design, input validation, and output formatting—but target different language ecosystems.

Input validation uses type schemas: Pydantic models in Python (FastMCP) or Zod in TypeScript (MCP SDK). Define strict schemas for each tool parameter, include descriptive annotations, and enforce validation at registration time. Standardized output formatting and error handling ensure LLMs receive predictable, safe responses.

Yes. MCP servers support both stdio (local) and streamable HTTP transports. HTTP transport lets you expose the server remotely, enabling distributed tool access. Configure the transport when initializing your server in FastMCP or MCP SDK.

Implement pagination for large data sets, validate all inputs against strict schemas, sanitize external data before returning it to LLMs, and use standardized naming conventions for tool discovery. Apply consistent error handling to prevent information leakage and follow safe data handling patterns throughout.

You can start from scratch. MCP server scaffolding in FastMCP and MCP SDK handles initial setup and tool registration. Begin with a sample tool, define its input schema and annotations, and run the server locally. Gradually add real tools connecting to your APIs or data sources.