[johnchristopher]

Fast is not a KPI though. It can and is often labeled on anything, making the term useless even when fast is a criteria over ease of us.

Maybe something at the top along the lines of : what it does, how and then what are the implications.

[mikepurvis]

Claiming "fast" implies that performance is a project goal, possibly even tracked over time as a metric, and that there's probably a comparison deeper in the README or elsewhere. It probably also means that when it comes to tradeoffs (compile time, code size, binary size, ergonomics, maybe even strictness/correctness), runtime speed is the preferred option.

[jeddy3]

"[description], aimed at speed" or something like that is better in that case, IMHO.