Rate limit

A rate limit restricts how many requests a service will handle from a browser or other program during a period of time. A service can use limits to manage capacity or discourage automated data collection and abuse. If a request is refused because the limit was reached, the response does not tell you that the domain or data you asked about is invalid.

What does a rate-limit response look like?

An HTTP service may return 429 Too Many Requests. The response may include a Retry-After value that tells the client how long to wait before trying again. For example, an RDAP lookup service may limit repeated registration-data queries. The client should slow down and honor the wait instruction rather than treating the unanswered query as “domain not found.”

Not every service uses the same limit or response. Some may return another status or stop responding. A rate limit can apply to one account, address, particular service function, or whole service, depending on the operator's policy.

How is a rate limit different from a timeout?

A 429 response explicitly says that the service is limiting requests. A timeout means the checker did not receive a usable response in time. If a tool reports only “rate limited,” look for the source and any retry guidance before drawing conclusions about the requested data.

Related terms

• RDAP — registration lookups may be rate limited
• Timeout — no usable response arrived in time
• Incomplete check result — the query did not establish the requested fact