> For clean Markdown content of this page, append .md to this URL. For the complete documentation index, see https://buildwithfern.com/learn/llms.txt.

# Download OpenAPI spec

> Fern serves your OpenAPI 3.1 spec from your docs site so AI tools and LLMs can discover and interact with your API programmatically.

Fern docs sites automatically serve your raw OpenAPI 3.1 specification, so anyone — or any tool — can download it for SDK generation, contract testing, or importing into tools like Postman.

The spec is also linked from your site's [`llms.txt`](/learn/docs/ai-features/llms-txt), so AI coding assistants like Cursor, Copilot, and Claude can discover and use it to generate accurate API calls and build integrations.

## Available endpoints

Every Fern docs site exposes the OpenAPI specification at these paths:

| Endpoint        | Format | Content-Type         |
| --------------- | ------ | -------------------- |
| `/openapi.json` | JSON   | `application/json`   |
| `/openapi.yaml` | YAML   | `application/x-yaml` |
| `/openapi.yml`  | YAML   | `application/x-yaml` |

The spec includes your endpoints with request/response schemas, authentication schemes (Bearer, Basic, API Key, OAuth), webhooks, type definitions as component schemas, and server URLs from your environment configuration. The [`info.version`](/learn/api-definitions/openapi/extensions/api-version) field from your source spec is preserved as-is, including non-SemVer formats like CalVer. The spec is generated from the same API definition that powers your docs, so it's always up to date.

Endpoints and API references marked `hidden: true` are excluded.

## Usage

Append the endpoint to your docs URL to download the spec:

```bash
# Download as JSON
curl https://your-docs-site.com/openapi.json

# Download as YAML
curl https://your-docs-site.com/openapi.yaml
```

If your docs site includes multiple API definitions, the endpoint returns a listing of available APIs. To select a specific one, use the path-based form, which serves the spec directly and is CDN-friendly:

```bash
curl https://your-docs-site.com/openapi/my-api-id.json
```

The `my-api-id` segment resolves against an API's slug, title, or UUID.

If your docs site has password or SSO authentication configured, the spec endpoints inherit that authentication and return `401` to unauthenticated requests.

> Fern serves your OpenAPI 3.1 spec from your docs site so AI tools and LLMs can discover and interact with your API programmatically.