API Doctor MCP

A deterministic, stateless MCP server for validating OpenAPI documents, JSON Schemas, and JSON payloads.

It uses Python libraries only. It does not call an LLM, persist user data, or require login.

Current tools

• validate_openapi

• list_openapi_endpoints

• compare_openapi_specs

• view_openapi_breaking_changes

• validate_json_schema

• validate_payload

Architecture

MCP transport
    -> ServerFactory
        -> ToolProvider discovery
            -> Handlers
                -> Services
                    -> Validators / Comparators

Important properties:

• Stateless: no database, sessions, cache, or persistent files.

• Open/Closed: add a new IToolProvider implementation; discovery registers it automatically.

• Dependency Inversion: handlers depend on service interfaces, not concrete libraries.

• Strategy: parsers, validators, and comparison rules are replaceable strategies.

• Factory: application and server creation are centralized.

• Adapter: third-party validation libraries are hidden behind internal interfaces.

• Class-based: application behavior is represented by classes and objects.

• CamelCase Python filenames: used as explicitly requested.

Run locally

uv sync --extra dev
uv run uvicorn app.Main:app --host 0.0.0.0 --port 8085

MCP endpoint:

http://localhost:8085/mcp

Health endpoint:

http://localhost:8085/health

The server uses the MCP Python SDK v2 beta and exposes one Streamable HTTP application. Modern 2026-07-28 requests are sessionless. stateless_http=True also prevents legacy clients from creating retained HTTP sessions.

MCP HTTP usage

The callable MCP endpoint is:

http://localhost:8085/mcp

This server uses the modern stateless MCP HTTP format for protocol version 2026-07-28.

Each MCP request is a single HTTP POST with:

• header Content-Type: application/json

• header Accept: application/json, text/event-stream

• header mcp-protocol-version: 2026-07-28

• header mcp-method: <json-rpc-method>

• header mcp-name: <tool-name> for tools/call requests

• JSON-RPC body containing params._meta

See MCP_API.md for complete request and response examples for:

• tools/list

• validate_json_schema

• validate_payload

• validate_openapi

• list_openapi_endpoints

• compare_openapi_specs

• view_openapi_breaking_changes

MCP Apps

This repo now includes one MCP App:

• view_openapi_breaking_changes

It follows the MCP Apps pattern described in the official docs:

• the tool advertises _meta.ui.resourceUri

• the server exposes a ui://... resource

• the host fetches and renders the bundled HTML app in a sandboxed iframe

The bundled app source lives in:

mcp_apps/breaking-change-viewer/

Build the app bundle:

make app-build

The built artifact served by the Python MCP server is:

mcp_apps/breaking-change-viewer/dist/mcp-app.html

Test with basic-host

The easiest local host-level test path is the MCP Apps basic-host.

1. Start this server:

make run

2. In another folder, clone the MCP Apps repository and start the host:

git clone https://github.com/modelcontextprotocol/ext-apps.git
cd ext-apps/examples/basic-host
npm install
SERVERS='["http://localhost:8085/mcp"]' npm start

3. Open:

http://localhost:8080

4. Select and call view_openapi_breaking_changes

When the host calls the tool, it should fetch the ui://... resource and render the Breaking Change Diff Viewer inline.

Test

uv run pytest
uv run ruff check .
uv run mypy app

Docker

docker compose up --build

Add a tool without modifying existing code

1. Add a service interface and implementation, when needed.

2. Add a handler class.

3. Add a concrete class implementing IToolProvider under app/ToolProviders.

4. Give the provider a parameterless constructor.

5. The provider-discovery mechanism imports and registers it automatically.

Providers receive the application ServiceContainer during registration.

Production note

The pinned MCP SDK is a prerelease. Upgrade the exact pin deliberately after testing API changes.