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HTTP Header
Priority
RequestAllows clients to signal the relative priority of an HTTP request.
HTTP header reference, syntax, examples, and developer usage.
What is the Priority header?
The Priority HTTP header is used to transmit metadata between a client and server as part of HTTP requests or responses.
HTTP headers define how content should be interpreted, cached, authenticated, secured, or processed by browsers and APIs.
Direction
This is a request header sent by the client to the server.
Syntax
Priority: u=<urgency>, i
Example
Priority: u=1, i
Common use cases
- Prioritizing critical resources like fonts or above-the-fold images
- Deprioritizing background fetch requests
- Improving page load performance in HTTP/2 and HTTP/3
Common mistakes
- Using the header in the wrong request or response context
- Sending invalid header values
- Incorrect header syntax
- Assuming the header automatically changes server behaviour
Practical developer insight
Priority replaces the older HTTP/2 stream priority mechanism. The u parameter sets urgency from 0 (highest) to 7 (lowest), with a default of 3. The i flag marks a resource as incremental. Adoption is still evolving — most relevant in browser-server communication rather than typical application-level code.