Accept Header

How Accept works

Servers use it for content negotiation, for example returning JSON to API clients and HTML to browsers from the same URL. q values from 0 to 1 rank alternatives. Browsers send a long default for navigation that prefers HTML, and advertise image formats such as AVIF and WebP on image requests.

Examples

Accept: application/json

Accept: application/json, text/plain;q=0.9, */*;q=0.8

Common mistakes

• If the server can’t produce any acceptable format it may answer 406 Not Acceptable, but most just send their default.

Check it

# Show the request headers curl sends (lines starting with >)
curl -sv -o /dev/null https://example.com 2>&1 | grep '^>'

Paste a full set of response headers into the HTTP header checker to get every header explained and common mistakes flagged.

Related headers

• Content-Type: states the media type (MIME type) of the body, and for text, its character encoding.
• Accept-Encoding: lists the compression formats the client can decode.
• Accept-Language: lists the user’s preferred languages, from the browser or OS settings.
• Vary: lists the request headers that change the response, so caches keep a separate copy for each value.

More content and negotiation headers

Content-Disposition , Content-Encoding , Content-Length , Range , Transfer-Encoding .

Sources

• RFC 9110
• MDN: Accept

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Frequently asked questions