This is the metadata and OpenAPI spec I created for a custom ChatGPT plugin (or GPT, as OpenAI calls them) that can search your Raindrop.io bookmark library for you. It is tested and working, albeit with mixed results when dealing with large amounts of tags and collections. With further tuning of the system prompt and OpenAPI spec, it could be vastly improved.
Here is the unpublished plugin: https://chat.openai.com/g/g-uNdVJh9vu-raindrop-io-search-assistant
I will update it if I ever get the OAuth to work, until then, it won't work unfortunately.
I decided against publishing on the 'GPT Store' because I could not get the OAuth login to work despite following Raindrop.io and OpenAI documentation closely. Also, such an integration should probably be provided by the Raindrop.io devs anyways.