feat: adding document on how to down the openapi spec

docs/.vitepress/config.mts

@@ -767,6 +767,7 @@ export default withMermaid(
                 items: [{ text: "For Claude Code", link: "/dev-tools/mcp-server-claude-code" }],
               },
               { text: "Plane Compose", link: "/dev-tools/plane-compose" },
+              { text: "OpenAPI Specification", link: "/dev-tools/openapi-specification" },
               { text: "Webhooks", link: "/dev-tools/intro-webhooks" },
             ],
           },

docs/dev-tools/openapi-specification.md

@@ -0,0 +1,67 @@
+---
+title: OpenAPI Specification
+description: Generate and access the OpenAPI 3.0 specification for the Plane public REST API using drf-spectacular.
+keywords: plane, developer tools, openapi, api specification, swagger, redoc, drf-spectacular, api documentation
+---
+
+# OpenAPI Specification
+
+Plane uses [drf-spectacular](https://drf-spectacular.readthedocs.io/) to generate an OpenAPI 3.0 specification for the public REST API (`/api/v1/`). The feature is **disabled by default** and must be explicitly enabled.
+
+## Enable the OpenAPI spec
+
+Add the following to your `.env` file (at the project root or `apps/api/.env`):
+
+```env
+ENABLE_DRF_SPECTACULAR=1
+```
+
+Then restart the API server so it picks up the new variable.
+
+| Variable                 | Required value | Default | Description                                                  |
+| ------------------------ | -------------- | ------- | ------------------------------------------------------------ |
+| `ENABLE_DRF_SPECTACULAR` | `1`            | `0`     | Activates drf-spectacular and registers the schema endpoints |
+
+No other environment variables are needed — everything else (schema path prefix, tags, auth schemes, servers) is pre-configured in `apps/api/plane/settings/openapi.py`.
+
+## Access the OpenAPI spec
+
+> Replace `{domain_name}` below with your self-hosted Plane domain (e.g. `plane.example.com`).
+
+Once the API server is running with the variable enabled, three endpoints are available:
+
+| Endpoint                      | URL                                            | Description                |
+| ----------------------------- | ---------------------------------------------- | -------------------------- |
+| `GET /api/schema/`            | `https://{domain_name}/api/schema/`            | Raw OpenAPI schema (YAML)  |
+| `GET /api/schema/swagger-ui/` | `https://{domain_name}/api/schema/swagger-ui/` | Interactive Swagger UI     |
+| `GET /api/schema/redoc/`      | `https://{domain_name}/api/schema/redoc/`      | ReDoc documentation viewer |
+
+## Download the OpenAPI spec
+
+### Browser
+
+Open `https://{domain_name}/api/schema/` and save the page. The default format is YAML.
+
+For JSON, append the `format` query parameter:
+
+```text
+https://{domain_name}/api/schema/?format=openapi-json
+```
+
+### curl
+
+```bash
+# YAML
+curl -o openapi.yaml https://{domain_name}/api/schema/
+
+# JSON
+curl -o openapi.json https://{domain_name}/api/schema/?format=openapi-json
+```
+
+### Management command (offline, no running server required)
+
+```bash
+# From apps/api/
+ENABLE_DRF_SPECTACULAR=1 python manage.py spectacular --file openapi.yaml
+ENABLE_DRF_SPECTACULAR=1 python manage.py spectacular --file openapi.json --format openapi-json
+```