Sliding window

Sliding window counting blends the previous and current time chunks. It avoids the sharp reset of a fixed window without storing an entry for every request.

Use it when

• Boundary fairness matters more than minimal computation.
• You want smoother API traffic.
• A close approximation of the recent request count is acceptable.

const limiter = createRateLimiter({
  algorithm: Algorithms.SLIDING_WINDOW,
  limit: 100,
  windowMs: 60_000,
  store,
});

The admission check includes the request currently being evaluated, so the estimated count never exceeds limit after a request is allowed — a request that would push the weighted estimate over the limit is denied rather than admitted first and accounted for afterward.

The algorithm is an approximation. Document that trade-off anywhere your limits form part of a customer-facing contract.