Priority

BothActive

The Priority header (RFC 9218) provides a standardized way for clients to signal request priority to servers and intermediaries. It replaces HTTP/2's internal PRIORITY frames and works across HTTP/1.1, HTTP/2, and HTTP/3. Parameters: urgency (0-7, lower is more urgent), incremental (whether partial responses are useful).

Priority: u=<urgency>[, i[=<true|false>]]

Description

Priority is an extensible priority signal. The urgency parameter (0-7) maps roughly to: 0=blocking resources, 1=critical render path, 2=above-fold images, 3=default, 4=lazy-load, 5=prefetch, 6=background, 7=lowest. The incremental parameter indicates whether incremental delivery (partial response) is useful – true for streaming media, false for blocking scripts. Chrome and Cloudflare both implement Priority.

Directives

Directive	Description
u=<0-7>	Urgency level. 0 = highest, 7 = lowest. Default: 3.
i	Incremental. Partial responses are useful (e.g., streaming).

Examples

Critical resource

http

GET /styles/critical.css HTTP/1.1
Priority: u=0

Lazy-load image

http

GET /images/hero.webp HTTP/1.1
Priority: u=4, i

Specification

RFC 9218 – Priority specification →