kb/data/developer.mozilla.org/en-US/docs/Glossary/Quality_values-0.md

title	chunk	source	category	tags	date_saved	instance
Quality values - Glossary | MDN	1/3	https://developer.mozilla.org/en-US/docs/Glossary/Quality_values	reference	web, html, css, javascript, documentation	2026-05-05T05:41:38.456374+00:00	kb-cron

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1. Glossary
2. Quality values

Quality values

Quality values , or q-values and q-factors , are used to describe the order of priority of values in a comma-separated list. It is a special syntax allowed in some HTTP headers and in HTML. The importance of a value is marked by the suffix ';q=' immediately followed by a value between 0 and 1 included, with up to three decimal digits, the highest value denoting the highest priority. When not present, the default value is 1.

In this article

• Examples
• More information

Examples

The following syntax indicates the order of priority:

Value	Priority
text/html and application/xhtml+xml	1.0
application/xml	0.9
*/*	0.8
If there is no priority defined for the first two values, the order in the list is irrelevant. Nevertheless, with the same quality, more specific values have priority over less specific ones:
Value	Priority
---	---
text/html	0.8 (but totally specified)
text/*	0.8 (partially specified)
*/*	0.8 (not specified)
Some syntax, like the one of Accept, allow additional specifiers like text/html;level=1. These increase the specificity of the value. Their use is extremely rare.

More information

• HTTP headers using q-values in their syntax: Accept, Accept-Encoding, Accept-Language, TE.
• Header field definitions.