---
title: Why your browser asks about uploading
nav: That upload prompt
order: 2
description: Chrome and Firefox show a fixed warning whenever a page asks to read a whole folder. It describes what the page could do, not what it is doing — and the page can neither suppress it nor reword it. Plus how to verify for yourself that nothing is sent.
updated: 2026-08-29
---

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.

## Your browser said that, not the page

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.

## What the tool actually does

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.

## How to verify it yourself

Don't take this page's word for it — look:

1. Press `F12` to open DevTools and switch to the **Network** tab
2. Tick “preserve log”, then pick a folder and browse a few images
3. Watch for any request going out

All you will see is the initial page load. Picking files and browsing them produces no new
network requests at all.

## Why not use the API that doesn't warn

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.)

## By the way: it cannot even modify your files

`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](/en/mdeditor/docs), *can* overwrite files on your
disk — but that uses a different API which requires its own explicit grant, and asks every time.)