Subreddit search vs site-wide search vs the subreddit feed — what's the difference?

GET /v1/reddit/subreddits/search needs a known subreddit and an optional query, for when you're scoped to one community. GET /v1/reddit/search is site-wide keyword search (required query, 1–512 characters) for when a phrase could show up in any subreddit. GET /v1/reddit/subreddits/{subreddit}/posts is that community's ranked feed with no search query at all. Pick by whether you already know the community and whether you have a keyword.