Thoughts filed in: Hackery

15
Oct

Cookies can't be more than 4KiB in size

Did you know: you can't reliably store more than 4KiB (4096 bytes) of data in a single browser cookie? I didn't until this week.

What, I can't have my giant cookie and eat it too? Outrageous!

What, I can't have my giant cookie and eat it too? Outrageous!

Image source: Giant Chocolate chip cookie recipe.

I'd never before stopped to think about whether or not there was a limit to how much you can put in a cookie. Usually, cookies only store very small string values, such as a session ID, a tracking code, or a browsing preference (e.g. "tile" or "list" for search results). So, usually, there's no need to consider its size limits.

However, while working on a new side project of mine that heavily uses session storage, I discovered this limit the hard (to debug) way. Anyway, now I've got one more adage to add to my developer's phrasebook: if you're trying to store more than 4KiB in a cookie, you're doing it wrong.