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Website Contacts APIRate limiting
Capping how many requests a client may make in a period, and rejecting the rest, usually with HTTP status 429.
Last updated September 28, 2026.
Definition
What Rate limiting means
APIs and websites limit how fast a client may send requests, to protect their servers and share capacity fairly. A client over the limit gets an error, by convention HTTP 429 Too Many Requests, often with a Retry-After header saying when to try again.
Well-behaved clients retry with a growing delay, called exponential backoff, and spread scheduled jobs out rather than starting them all at once.
Clair returns 429 with quota_exceeded when a key has used the requests its plan allows, and a Retry-After header where the reset time is known.
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Each Clair API is its own monthly request quota. Unused requests expire. Every API has a free tier to try it.