State type and size limits before the file is chosen
Aliases: accept attribute · file too large after select · upload limits
What it is
Before opening a folder, people need to know what this intake takes: types, maximum size, how many. A “.heic not supported” or “over 5 MB” after the choice—or after the transfer—makes them pay for a search that cannot succeed. Pre-choice file constraints write the rules on the intake, ahead of the system picker and the drop. The issue is when the limit appears, not whether click and drop both exist, and not how to retry after failure.
Why it happens
Picking a file is a costly search: recall the name, walk folders, wait for thumbnails. If the constraint appears after the search, the cost is already paid, plus “you could have said.” Type and size visible in advance change the search: people look for PDFs, check size first. The picker’s accept can grey illegal types, but size is rarely filtered there, so the page must say it. Phone libraries default to HEIC and large screenshots; without a prior statement those two refusals are stable. The copy must also match the real backend; 10 MB on the page and 2 MB at the gateway makes the prior notice a lie.
Where it stops holding
When types are extremely wide (“any attachment”), listing every MIME is noise; “common office formats, per-file cap” beats a catalogue. Virus scanning can only run after upload; that clause cannot be guaranteed before choice and should be separated as “we will still scan after transfer,” not pretended to be exhausted up front. Browsers honor accept unevenly; greying is not a hard stop, so the prior copy must still be readable. Files arriving from a messenger “share to app” never passed your intake; show the constraint again on the landing view.
Applying it
- Write type, size, and count beside the choose button and drop region; do not save the first telling for a red line.
- Keep
acceptaligned with that copy, and re-check size on the client immediately after choice with the same rule. - Use phrasing people can use (“PDF or JPG, each under 5 MB”), not a MIME string alone.
- Verify by asking, with no file chosen, “what can go here?” If the answer disagrees with the real rejection rule, the constraint still lives in failure. Then pick an oversize file and see whether refusal happens before the transfer starts or after the bar completes.