mcp-openapi
Turn any OpenAPI/Swagger spec into MCP tools. Zero config, zero code.
Documentation
mcp-openapi
> Turn any OpenAPI/Swagger spec into MCP tools — so Claude and other AI assistants can call your REST APIs.
Point `mcp-openapi` at any OpenAPI 3.x or Swagger 2.0 spec URL and it generates Model Context Protocol (MCP) tools automatically. No code generation, no config files, no boilerplate. Your AI assistant gets callable tools for every API endpoint in seconds.
Quick Start
1. Run it (no install required):
npx mcp-openapi --spec https://petstore3.swagger.io/api/v3/openapi.json2. Add it to Claude Desktop (`claude_desktop_config.json`):
{
"mcpServers": {
"petstore": {
"command": "npx",
"args": [
"mcp-openapi",
"--spec", "https://petstore3.swagger.io/api/v3/openapi.json"
]
}
}
}3. Ask Claude to use it:
> "List all available pets in the store"
Claude sees MCP tools like `find_pets_by_status`, `get_pet_by_id`, `add_pet` and calls them directly.
Why mcp-openapi?
Most MCP-to-API bridges require you to write tool definitions by hand or generate code from a spec. `mcp-openapi` skips all of that.
| Feature | mcp-openapi | Hand-written MCP servers | Generic HTTP tools |
|---|---|---|---|
| Zero config setup | Yes | No | Partial |
| OpenAPI 3.x + Swagger 2.0 | Yes | N/A | N/A |
| Flat parameter schemas (LLM-optimized) | Yes | Manual | No |
| Smart tool naming from operationId | Yes | Manual | No |
| Auth (API key, Bearer, OAuth2) | Built-in | DIY | DIY |
| Retry with exponential backoff | Built-in | DIY | DIY |
| Response truncation for LLM context | Built-in | DIY | No |
Flat parameter schemas are the key differentiator. Instead of passing nested JSON objects (which LLMs frequently get wrong), `mcp-openapi` flattens path, query, header, and body parameters into a single flat object. This dramatically improves tool-calling accuracy.
How It Works
OpenAPI/Swagger Spec mcp-openapi AI Assistant
(URL or file) (Claude, etc.)
| | |
| 1. Parse & validate | |
|------------------------>| |
| | |
| 2. Generate MCP tools | |
| (one per endpoint) | |
|------------------------>| |
| | |
| | 3. Register tools |
| | via stdio transport |
| |------------------------>|
| | |
| | 4. AI calls a tool |
| ||------------------------>|Each API endpoint becomes one MCP tool:
- Tool name is derived from `operationId` (converted to `snake_case`) or from `method + path`
- Parameters are flattened into a single input schema (path, query, header, and body params merged)
- Responses are truncated to ~50KB to stay within LLM context limits
- Errors (429, 5xx) trigger automatic retries with exponential backoff (up to 3 retries)
Claude Desktop Integration
Add any API to Claude Desktop by editing your config file:
Location:
- macOS: `~/Library/Application Support/Claude/claude_desktop_config.json`
- Windows: `%APPDATA%\Claude\claude_desktop_config.json`
Public API (no auth)
{
"mcpServers": {
"petstore": {
"command": "npx",
"args": [
"mcp-openapi",
"--spec", "https://petstore3.swagger.io/api/v3/openapi.json"
]
}
}
}API with Bearer Token
{
"mcpServers": {
"github": {
"command": "npx",
"args": [
"mcp-openapi",
"--spec", "https://raw.githubusercontent.com/github/rest-api-description/main/descriptions/api.github.com/api.github.com.json",
"--auth-type", "bearer",
"--auth-token", "$GITHUB_TOKEN",
"--prefix", "github",
"--include", "listReposForAuthenticatedUser,getRepo,listIssues,createIssue"
],
"env": {
"GITHUB_TOKEN": "ghp_your_token_here"
}
}
}
}API with API Key
{
"mcpServers": {
"weather": {
"command": "npx",
"args": [
"mcp-openapi",
"--spec", "https://api.weather.example.com/openapi.json",
"--auth-type", "api-key",
"--auth-name", "X-API-Key",
"--auth-value", "$WEATHER_API_KEY",
"--auth-in", "header"
],
"env": {
"WEATHER_API_KEY": "your_key_here"
}
}
}
}CLI Reference
npx mcp-openapi --spec [options]General Options
| Option | Short | Default | Description |
|---|---|---|---|
| `--spec ` | `-s` | *required* | OpenAPI spec URL or local file path |
| `--config ` | `-c` | JSON config file path | |
| `--base-url ` | from spec | Override the API base URL | |
| `--prefix ` | Prefix for all tool names (e.g. `github` -> `github_list_repos`) | ||
| `--include ` | all | Comma-separated operationIds to include | |
| `--exclude ` | none | Comma-separated operationIds to exclude | |
| `--timeout ` | `30000` | HTTP request timeout in milliseconds | |
| `--max-retries ` | `3` | Max retries on 429/5xx responses | |
| `--header ` | `-H` | Custom header (repeatable) | |
| `--transport ` | `stdio` | Transport type: `stdio` or `sse` | |
| `--port ` | `3000` | Port for SSE transport | |
| `--help` | `-h` | Show help | |
| `--version` | `-v` | Show version | |
| `--license-key ` | Pro license key (or `$MCP_OPENAPI_LICENSE_KEY` env) | ||
| `--server ` | `0` | Select API server by index, partial URL, or exact URL | |
| `--no-doc-warnings` | Suppress doc quality warnings on startup | ||
| `--dynamic-discovery` | auto (100+) | Enable dynamic tool discovery for large APIs |
Auth Options
Bearer token:
| Option | Description |
|---|---|
| `--auth-type bearer` | Use Bearer token authentication |
| `--auth-token ` | The token value (supports `$ENV_VAR` syntax) |
API key:
| Option | Description |
|---|---|
| `--auth-type api-key` | Use API key authentication |
| `--auth-name ` | Header or query parameter name |
| `--auth-value ` | The API key value (supports `$ENV_VAR` syntax) |
| `--auth-in ` | Where to send the key (default: `header`) |
OAuth2 client credentials:
| Option | Description |
|---|---|
| `--auth-type oauth2` | Use OAuth2 client credentials flow |
| `--auth-client-id ` | OAuth2 client ID |
| `--auth-client-secret ` | OAuth2 client secret |
| `--auth-token-url ` | Token endpoint URL |
| `--auth-scopes ` | Comma-separated scopes |
CLI Examples
# Basic usage with a remote spec
npx mcp-openapi --spec https://petstore3.swagger.io/api/v3/openapi.json
# Local YAML spec with Bearer auth
npx mcp-openapi --spec ./api.yaml --auth-type bearer --auth-token '$API_KEY'
# Filter to specific endpoints with a prefix
npx mcp-openapi --spec ./api.json --prefix myapi --include 'listUsers,getUser'
# Override base URL (useful for local dev)
npx mcp-openapi --spec https://api.example.com/openapi.json --base-url http://localhost:3000
# Add custom headers
npx mcp-openapi --spec ./api.json -H 'X-Custom: value' -H 'X-Another: value2'
# Use a JSON config file
npx mcp-openapi --config ./mcp-config.json
# Select staging server
npx mcp-openapi --spec ./api.json --server staging
# Large API with dynamic discovery
npx mcp-openapi --spec https://api.stripe.com/openapi.json --dynamic-discoveryConfig File Format
Instead of CLI flags, you can use a JSON config file:
{
"spec": "https://api.example.com/openapi.json",
"prefix": "myapi",
"include": ["listUsers", "getUser", "createUser"],
"auth": {
"type": "bearer",
"token": "$API_TOKEN"
},
"timeout": 15000,
"maxRetries": 2,
"headers": {
"X-Custom-Header": "value"
}
}CLI arguments take precedence over config file values.
Supported Specs
| Format | Versions | File types |
|---|---|---|
| OpenAPI | 3.0.x, 3.1.x | `.json`, `.yaml`, `.yml` |
| Swagger | 2.0 | `.json`, `.yaml`, `.yml` |
Specs can be loaded from:
- Remote URLs (`https://...`)
- Local file paths (`./api.yaml`, `/absolute/path/spec.json`)
v0.3.0 Features
Doc Quality Warnings
On startup, `mcp-openapi` checks each tool's documentation quality. If endpoints have sparse descriptions (under 50 characters), you'll see a warning:
[mcp-openapi] WARN: Doc quality: 11 of 47 tools have sparse documentation ( Interested in Pro? Star the repo and [open an issue](https://github.com/Docat0209/mcp-openapi/issues) to get early access.
---
## Programmatic Usage
You can also use `mcp-openapi` as a library in your own MCP server:import { createServer } from 'mcp-openapi';
const { server, tools, spec } = await createServer({
spec: 'https://petstore3.swagger.io/api/v3/openapi.json',
prefix: 'petstore',
auth: {
type: 'bearer',
token: process.env.API_TOKEN,
},
});
console.log(`Loaded ${tools.length} tools from ${spec.info.title}`);
---
## Requirements
- Node.js 18 or later
- An OpenAPI 3.x or Swagger 2.0 spec (URL or local file)
---
## Contributing
Contributions are welcome. Here is how to get started:git clone https://github.com/Docat0209/mcp-openapi.git
cd mcp-openapi
pnpm install
pnpm test
pnpm build
Before submitting a PR:
1. Add tests for new features
2. Run `pnpm lint` and fix any issues
3. Follow [Conventional Commits](https://www.conventionalcommits.org/) for commit messages
---
## Related
- [graphql-to-mcp](https://www.npmjs.com/package/graphql-to-mcp) — Same zero-config approach for GraphQL APIs
## License
MIT
---
## Keywords
mcp, model-context-protocol, openapi, swagger, claude, ai, llm, api, tools, rest-api, ai-tools, mcp-serverFrequently asked questions
What is mcp-openapi?
mcp-openapi is Turn any OpenAPI/Swagger spec into MCP tools. Zero config, zero code.
How do I install mcp-openapi?
Open the GitHub repository and follow its README. Most MCP servers are added to your client's MCP config, then called by your agent.
Is mcp-openapi open source?
Yes — it is hosted on GitHub at https://github.com/Docat0209/mcp-openapi and has 3 stars.
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