Exceptions on App GW header field size limit ?

Question

Exceptions on App GW header field size limit ?

GONZALEZ ROMERO Juan Carlos 0

Hello all,

we have this situation where our application is behind App GW & WAF. For a particular query, the API needs to send a oslc.select field weighting 14kb (with the total header being 15kb) - so we are hitting the 8kb per field limitation on Azure.
Is there any way to bypass this limitation so the query does work ?

Thanks in advance.

Vinodh247-1375 43,586 Reputation points Volunteer Moderator

2026-07-29T04:30:17.82+00:00
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2 answers

Your answer

Vinodh247-1375 43,586 Reputation points Volunteer Moderator

2026-07-29T04:30:17.82+00:00

Please confirm if you had a chance to try any of the suggestions provided for your question.

Please 'Upvote'(Thumbs-up) and 'Accept' as answer if the reply was helpful.

If in case you have any resolution please share the same here with the community as it can be helpful to others. Else, please respond with more details and we will try to see if we can help further.

Answer 1

Hi ,

Thanks for reaching out to Microsoft Q&A.

No, you cannot bypass or increase the 8 KB per header field limit in azure application gateway, it is a hard platform constraint (applies regardless of WAF on/off). This is not configurable. The only viable approach is to redesign the request: move the large oslc.select payload out of headers into the request body (POST instead of GET), compress or shorten the field, or pass a reference/token that the backend resolves. If you must keep large headers, you need to avoid app gateway entirely (ex: route via azure front door or a custom proxy), but even then downstream services may enforce similar limits, so redesign is the realistic fix.

Please 'Upvote'(Thumbs-up) and 'Accept' as answer if the reply was helpful. This will be benefitting other community members who face the same issue.

Answer 2

Hi, Application Gateway's header limits are platform limits; there is not normally a per-listener exception you can request. First identify whether the failure is one oversized header (often Cookie or Authorization) or the total request headers by capturing the gateway access log/status and a sanitized request. The durable fix is to reduce the header: trim cookies, avoid putting large claims/groups in tokens, use server-side session state, or send only the claims the backend needs. A rewrite rule can remove an unnecessary header, but it cannot help if the gateway rejects the request before rewrite processing. If the documented limit and observed behavior disagree, open a support case with a minimal reproduction and correlation/request ID.