API to MCP Server Skill

Convert OpenAPI v3 specifications into fully functional MCP (Model Context Protocol) servers using HAPI CLI — no code required.

Workflow

Phase 1: Environment Setup

1. Verify HAPI CLI installation

   hapi --version

   If not installed, install using:

   • Linux/macOS: curl -fsSL https://get.mcp.com.ai/hapi.sh | bash
   • Windows: irm https://get.mcp.com.ai/hapi.ps1 | iex
   • Docker: Use hapimcp/hapi-cli:latest image directly

2. Validate OpenAPI spec is v3.x (not v2/Swagger). HAPI requires OpenAPI 3.0+ specifications.

Phase 2: Local Development & Testing

1. Start local MCP server

   hapi serve <project-name> \
     --openapi <path-or-url-to-openapi-spec> \
     --url <backend-api-url> \
     --headless \
     --port 3030

2. Verify server health

   curl -s http://localhost:3030/health
   # Expected: 200 OK
   
   curl -s http://localhost:3030/mcp/ping
   # Expected: pong

3. Test MCP endpoint — The MCP transport is available at /mcp using Streamable HTTP:

   • POST /mcp — JSON-RPC messages
   • GET /mcp — Server info (returns 204)

Phase 3: Deployment

Choose deployment target based on requirements:

Option A: Cloudflare Workers (Recommended for simplicity)

1. Authenticate (first time only):

   hapi login

2. Deploy:

   hapi deploy \
     --openapi <path-or-url-to-openapi-spec> \
     --url <backend-api-url> \
     --name <worker-name> \
     --project <project-name>

3. Verify deployment:

   curl -s https://<worker-name>.<account>.workers.dev/health

Option B: Docker (Self-hosted)

docker run --name hapi-<project> -d --rm \
  -p 3030:3030 \
  hapimcp/hapi-cli:latest serve <project-name> \
  --openapi <openapi-url> \
  --url <backend-api-url> \
  --port 3030 \
  --headless

Phase 4: Verification Checklist

Before considering deployment complete:

• /health returns 200 OK
• /mcp/ping returns pong
• At least one tool call succeeds via MCP transport
• Error responses include actionable messages

Key Concepts

Headless Mode

Use --headless flag when the MCP server proxies requests to an existing backend API. Without this flag, HAPI serves the OpenAPI spec documentation UI.

Streamable HTTP Transport

HAPI uses Streamable HTTP (not stdio). MCP clients connect via HTTP POST to /mcp endpoint. SSE is supported for streaming responses.

OpenAPI Spec Sources

HAPI accepts specs from:

• Local file path: --openapi ./specs/api.yaml
• Remote URL: --openapi https://api.example.com/openapi.json
• Pre-loaded specs in ~/.hapi/specs/<project>/

References

For detailed documentation, consult:

• references/hapi-cli-commands.md — Complete CLI reference
• references/deployment-patterns.md — Docker & Cloudflare recipes
• references/troubleshooting.md — Common issues & fixes

Quick Examples

Petstore API (Demo)

hapi serve petstore \
  --openapi https://petstore3.swagger.io/api/v3/openapi.json \
  --url https://petstore3.swagger.io/api/v3 \
  --headless --port 3030

Custom API

hapi serve my-api \
  --openapi https://my-api.example.com/openapi.json \
  --url https://my-api.example.com \
  --headless --port 3030

Deploy to Cloudflare

hapi deploy \
  --openapi https://my-api.example.com/openapi.json \
  --url https://my-api.example.com \
  --name my-api-mcp