mcp-from-openapi
MCP ServerFreeProduction-ready library for converting OpenAPI specifications into MCP tool definitions
Capabilities10 decomposed
openapi-to-mcp schema transpilation with type preservation
Medium confidenceConverts OpenAPI 3.0/3.1 specifications into MCP-compliant tool definitions by parsing JSON Schema components, extracting endpoint metadata, and generating typed tool schemas that preserve parameter constraints, response types, and authentication requirements. Uses a multi-pass AST-like traversal to map OpenAPI path items, operation objects, and parameter definitions into MCP's tool input/output schema format while maintaining JSON Schema validation semantics.
Implements bidirectional schema mapping between OpenAPI's JSON Schema dialect and MCP's constrained tool schema format, preserving validation rules (minLength, pattern, enum) while adapting to MCP's flatter parameter structure; uses recursive schema resolution to handle $ref and allOf compositions
Directly targets MCP protocol with full type fidelity, whereas generic OpenAPI-to-LLM converters often lose schema constraints or require post-processing to work with MCP servers
batch api endpoint-to-tool mapping with parameter extraction
Medium confidenceProcesses all endpoints in an OpenAPI spec in a single pass, extracting path parameters, query parameters, request bodies, and response schemas for each operation, then maps them to individual MCP tool definitions with proper input/output typing. Handles HTTP method semantics (GET vs POST) and parameter location rules (path vs query vs header vs body) to generate contextually appropriate tool schemas.
Implements a single-pass traversal of OpenAPI operation objects with stateful parameter collection, distinguishing between path/query/header/body parameters and applying HTTP semantics rules (e.g., GET cannot have body) to generate valid MCP tool schemas without multiple passes
More efficient than manual tool definition or generic schema converters because it understands HTTP parameter semantics and MCP's specific tool schema constraints, avoiding invalid or malformed tool definitions
json schema to mcp input schema compilation with constraint preservation
Medium confidenceTranslates OpenAPI's JSON Schema definitions (including constraints like minLength, pattern, enum, required fields) into MCP's input schema format, preserving validation semantics while adapting to MCP's tool parameter structure. Handles nested objects, arrays, and schema composition patterns (allOf, oneOf, anyOf) by flattening or nesting appropriately for MCP's flat parameter model.
Implements recursive schema resolution with constraint mapping, translating OpenAPI's JSON Schema validation keywords (minLength, pattern, enum, required) into MCP's constrained parameter format while handling $ref dereferencing and schema composition without losing validation semantics
Preserves validation constraints that generic schema converters often drop, ensuring LLM agents receive accurate parameter guidance and reducing invalid API calls due to constraint violations
response schema extraction and output type generation
Medium confidenceExtracts response schemas from OpenAPI operation definitions (200, 201, 400, 500 status codes) and generates MCP tool output schemas that describe the expected return type and structure. Maps HTTP status codes to success/error outcomes and includes response headers and content-type information in the tool definition.
Extracts and maps HTTP status-specific response schemas from OpenAPI into MCP's single output schema format, using the most common success response (typically 200) as the primary output type while documenting error cases in tool descriptions
Provides type information for API responses that generic tool generators omit, enabling LLM agents to understand and validate response data before processing
authentication and security scheme mapping to mcp tool context
Medium confidenceParses OpenAPI security schemes (API keys, OAuth2, HTTP Basic, Bearer tokens) and generates MCP tool definitions that indicate required authentication context. Maps security requirements from OpenAPI to tool metadata that MCP servers can use to inject credentials or enforce authentication policies at runtime.
Maps OpenAPI security schemes to MCP tool metadata by extracting scheme type and requirements, then encoding them in tool descriptions and context fields that MCP servers can interpret to enforce authentication policies without modifying the tool schema itself
Explicitly documents authentication requirements in tool definitions, whereas generic converters often omit security context, leading to unauthenticated API calls or runtime failures
tool naming and description generation from openapi metadata
Medium confidenceGenerates human-readable tool names and descriptions from OpenAPI operation summaries, descriptions, and tags, creating clear, contextual naming that helps LLM agents understand tool purpose and usage. Uses operation summaries as tool descriptions and tags to organize tools into logical groups.
Extracts and adapts OpenAPI operation metadata (summary, description, tags) into MCP tool names and descriptions, applying length constraints and formatting rules specific to MCP while preserving semantic meaning from the original API documentation
Leverages existing OpenAPI documentation to create meaningful tool names and descriptions, whereas generic converters often generate generic or unhelpful names like 'call_endpoint_1', improving LLM agent tool selection accuracy
typescript type definition generation for tool inputs and outputs
Medium confidenceGenerates TypeScript interfaces and types for MCP tool inputs and outputs based on OpenAPI schemas, enabling type-safe tool implementations and client code. Produces .d.ts files or inline type definitions that match the generated MCP tool schemas, supporting both strict typing and optional fields based on OpenAPI requirements.
Generates TypeScript types that directly correspond to MCP tool input/output schemas, using recursive type generation for nested objects and applying OpenAPI constraints (required fields, enums) to produce strict, enforceable types
Provides TypeScript types specifically tailored to MCP tool schemas, whereas generic OpenAPI-to-TypeScript generators produce types for REST client libraries that don't map cleanly to MCP tool definitions
mcp server integration and tool registration
Medium confidenceProvides utilities to register generated MCP tools with an MCP server runtime, handling tool registration, input validation, and error handling. Includes adapters for popular MCP server frameworks and patterns for wrapping API calls with proper error handling and response transformation.
Provides framework-specific adapters and patterns for registering generated tools with MCP servers, handling the impedance mismatch between OpenAPI's REST semantics and MCP's tool calling interface with automatic request/response transformation
Simplifies MCP server setup by automating tool registration and providing pre-built integration patterns, whereas manual tool registration requires boilerplate code and error-prone configuration
openapi spec validation and compatibility checking
Medium confidenceValidates OpenAPI specifications for completeness and compatibility with MCP tool generation, checking for required fields (operationId, responses), detecting unsupported patterns, and providing warnings about potential conversion issues. Performs pre-flight validation before transpilation to catch spec errors early.
Performs MCP-specific validation checks on OpenAPI specs, identifying patterns that don't translate well to MCP (e.g., missing operationId, unsupported parameter locations) rather than generic OpenAPI validation
Catches MCP-specific compatibility issues early, whereas generic OpenAPI validators only check spec conformance and miss conversion-specific problems
incremental spec updates and tool regeneration
Medium confidenceSupports updating generated MCP tools when the OpenAPI spec changes, detecting which endpoints have been added, modified, or removed and regenerating only affected tools. Maintains tool definitions across updates while preserving custom modifications or metadata.
Implements spec diffing and selective tool regeneration, comparing OpenAPI specs to identify changed endpoints and regenerating only affected tools while preserving unchanged tool definitions and custom metadata
Enables efficient updates to tool definitions without full regeneration, whereas naive approaches regenerate all tools on every spec change, potentially losing custom modifications or creating unnecessary churn
Capabilities are decomposed by AI analysis. Each maps to specific user intents and improves with match feedback.
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Best For
- ✓Teams maintaining REST APIs who want to expose them to Claude/LLM agents via MCP
- ✓Developers building LLM agent frameworks that need to dynamically load API integrations
- ✓API-first companies automating tool generation for multiple LLM providers
- ✓API providers with large endpoint catalogs (50+ endpoints) needing bulk tool generation
- ✓MCP server developers building dynamic tool loaders from API specs
- ✓Teams automating integration testing between API specs and LLM tool definitions
- ✓API teams ensuring LLM agents respect parameter constraints and validation rules
- ✓Developers building type-safe MCP tool wrappers around REST APIs
Known Limitations
- ⚠OpenAPI 2.0 (Swagger) support may be limited or require pre-conversion to 3.0 format
- ⚠Complex discriminator patterns and polymorphic schemas may not fully transpile to MCP constraints
- ⚠Custom OpenAPI extensions outside standard spec are not preserved in MCP output
- ⚠No built-in handling for API authentication flows beyond basic header/query parameter mapping
- ⚠Large OpenAPI specs (>10MB) may cause memory overhead during parsing and transpilation
- ⚠Duplicate or conflicting endpoint definitions in the spec are not deduplicated automatically
Requirements
Input / Output
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Production-ready library for converting OpenAPI specifications into MCP tool definitions
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