Upload guidance
Understand YouTube thumbnail file limits, mobile upload risk, and when a smaller export is safer.
YouTube allows larger thumbnail files from desktop than from mobile. If you upload from a phone, keeping the file at 2 MB or less is the safer target. The thumbnail checker flags files that may be too large for mobile upload.
Do not shrink the file by crushing the image quality. Export a clean JPG or PNG, then check that the main subject still looks clear in a small preview.
A file can be small enough but still fail the job if it is the wrong shape or hard to read. Pair this guide with the safe zone guide before publishing.