What Is an HTTP Long Poll?

An HTTP long poll is one request a client makes that the server deliberately leaves unanswered until it has data to return or a maximum wait expires. It is the individual building block of the long polling loop, where each completed long poll is immediately followed by another. The mechanism relies only on standard HTTP request and response semantics.

Why it matters

Because a long poll is just a slow HTTP response, it passes through firewalls, proxies, and CDNs that block more exotic transports. That broad compatibility is why long polling remains a reliable fallback for near-real-time updates.

Related guides