gemini.google.com cannot call your API. Use Google AI Studio for notebook mode.

1. Open AI Studio → Tools → Add function.
2. Import or paste OpenAPI from https://guides.co/api/gdf/v1/openapi.json.
3. Auth header: Authorization: Bearer {your_gdf_key}.
4. Paste Studio Instructions for your AI into system instructions.
5. Test: "List my guides."