A rate limit is a cap on how many requests an app or service accepts in a set window of time, like 100 calls per minute. In app building, it protects your app and the services it depends on from being overwhelmed by too many requests at once.
Rate Limit
Why rate limits matter
When your app calls an outside service, that service often limits how often you can ask. Cross the line and requests start failing, usually with a "429 too many requests" error that can look like your app is broken.
Rate limits also protect your own app. Without one, a single user or a bad script can flood your backend with requests, slow everything down for everyone, and run up costs on the services you pay per call.
How rate limits work
A service counts requests coming from your app inside a rolling window. Each request adds to the count, and once you hit the ceiling, further requests are rejected until the window resets. The response usually says how long to wait before trying again.
Well-built apps respect these limits instead of fighting them. They slow their own request rate, spread calls out over time, and pair with retry logic so a rejected request is tried again politely rather than hammered through.
Rate limit examples
A weather app pulls forecasts from a third-party API capped at 60 calls per minute. On a busy morning, hundreds of users open the app at once and the app blows past 60, so the API starts returning errors. The fix is to cache each city's forecast for a few minutes, so repeated lookups reuse one stored result instead of making a fresh call every time.
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