What it is
throttle is a small Go package for limiting client-side work to a fixed number of operations per time window. It is safe for concurrent callers and includes an http.RoundTripper wrapper for applying the limit to outgoing HTTP requests.
The actual algorithm
The implementation uses a fixed-window counter. It tracks the beginning of the current window and the number of accepted operations inside it. Once the window expires, the counter resets; when the current window is full, callers wait for the next one.
This description follows the source. It deliberately avoids the repository README’s inconsistent use of “sliding window.”
A composable HTTP boundary
The transport wrapper applies waiting before delegating to another http.RoundTripper. That keeps throttling at the network boundary and allows it to compose with the standard Go HTTP client instead of requiring request sites to remember a separate limiter call.
What it illustrates
throttle is focused current work: a concurrency primitive with a small API, explicit algorithm, and an adapter for the standard interface where it is most useful.