I did this in about 400 or 500 lines of typescript with direct API calls into vertex AI (using a library for auth still). Supports zod for structured outputs (gemini 2.5 supports json schema proper, not just the openapi schemas the previous models did), and optionally providing tools or not. Includes a nice agent loop that integrates well with it and your tools get auto deserialized and strongly typed args (type inference in ts these days is so good). Probably could had been less if I had used googles genai lib and anthropic’s sdk - I didn’t use them because it really wasn’t much code and I wanted to inject auditing at the lowest level and know the library wasn’t changing anything.

If you really want a library, python has litellm, and typescript has vercel’s AI library. I am sure there are many others, and in other languages too.

Its a godforsaken nightmare.

There's a lotta potemkin villages, particularly in Google land. Gemini needed highly specific handholding. It's mostly cleared up now.

In all seriousness, more or less miraculously, the final Gemini stable release went from like 20%-30% success at JSON edits to 80%-90%, so you could stop doing the parsing Aider edits out of prose.

I recommend litellm if you’re writing Python code, since it handles provider differences for you through a common interface:

https://docs.litellm.ai/