Press “Choose folder” and your browser shows something like this:
Upload 128 files to this site?
It looks alarming. This tool uploads nothing. This chapter explains what that sentence is, and how to check for yourself.
When a page asks to read an entire folder rather than a single file, Chrome and Firefox show this warning. It is about scope of access: “you are about to hand this page the contents of every file in this folder, and it would be able to upload them.”
It is not a description of something happening. Much like your phone asking “allow this app to use the camera?” does not mean the camera is recording.
⚠️ A page cannot do anything about this dialog — it cannot intercept it, reword it, or declare in advance that it will not upload. All it can do is put a line of explanation next to the button, which is exactly what the small print in the tool is for.
Once it has the file list, everything happens through the browser's own local APIs:
| What you see | How it is produced |
|---|---|
| Thumbnails and previews | URL.createObjectURL opens the file in the browser |
| Name, size, date | The file object already carries these fields |
| Filtering, search, sorting | Operations on a list held in memory |
No step needs a server. This site's only job is to hand you one HTML file; after that it is out of the picture.
Don't take this page's word for it — look:
F12 to open DevTools and switch to the Network tabAll you will see is the initial page load. Picking files and browsing them produces no new network requests at all.
Chrome has another API (showDirectoryPicker) with a gentler prompt, but only Chromium-based
browsers have it — on Firefox and Safari the whole tool would simply not work.
webkitdirectory, which this tool uses, is supported far more widely. The alarming dialog is
the price. Given the choice, it went with “works for more people” plus a line of explanation.
(You can have both via progressive enhancement: use showDirectoryPicker when it exists and
fall back to webkitdirectory. That is a separate piece of work and is not done today.)
webkitdirectory hands over a read-only snapshot. This tool cannot rename, delete, move or
write anything — it does not have the permission, whatever it might want.
(Another tool on this site, Markdown Editor, can overwrite files on your disk — but that uses a different API which requires its own explicit grant, and asks every time.)
Download this page as .md Open it in the editor and you have a ready-made sample document.