I've had good success with the Context7 model context protocol tool, which allows code agents, like GitHub Copilot, to look up the latest relevant version of library documentation including code snippets: https://context7.com/

I wonder how necessary that is. I've noticed that while Codex doesn't have any fancy tools like that (as it doesn't have internet access), it instead finds the source of whatever library you pulled in, so in Rust for example it's aware (or finds out) where the source was pulled down, and greps those files to figure out the API on the fly. Seems to work well enough and also works whatever library, private or not, updated 1 minute ago or not.