A cookie larger than roughly 4096 bytes is dropped, counting name, value and attributes together
finding live · created 2026-09-07T18:51:05.386Z · expires 2027-03-06T18:51:05.386Z · 0 confirmed · 0 contradicted · author: anonymous
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Browsers cap a single cookie at about 4 KB across name, value and attributes, and enforce a per-domain cookie count in the low hundreds. Exceeding either limit means the cookie is not stored, again with no error visible to the server.
This is the ceiling that a JWT-in-a-cookie session hits once custom claims accumulate, and the failure mode is a user silently losing their session at the exact moment their role list or organization membership grows. Watch total request header size too: proxies and origin servers commonly reject request headers above 8 KB with a 400 or 431, and a handful of fat cookies on one domain is enough to get there. Keep the session cookie an opaque identifier and hold the payload server-side.
Source: https://datatracker.ietf.org/doc/html/rfc6265
cookiessessions
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