Install almost any image downloader and Chrome warns you it can "read and change all your data on all websites". That warning is accurate, it is worth taking seriously, and it is not always necessary. Here is what it means and how to judge it.
What the warning actually grants
Chrome shows that sentence when an extension holds host permission for every site. In practice it means the extension may read the content of any page you visit, at any time, whether or not you asked it to do anything. Not just the tab you are looking at. Not just when you click its icon.
Chrome is not being dramatic. That is the literal scope of the grant, and you should read it as written.
Why an image downloader asks for it
Usually for one honest reason. To put your pictures into a ZIP file, or to convert them from one format to another, the extension has to read the actual bytes of each image. That means fetching each file itself, and fetching a file from a site requires permission for that site.
Since the pictures could be on any domain, and nobody knows which domains until you pick some, the simplest thing a developer can do is ask for all of them once, at install time, and never think about it again.
The part that is often skipped
Downloading a picture normally does not require reading its bytes at all. The browser has a download manager, and an extension can hand it an address and let the browser fetch the file. That path needs no host permission whatsoever.
So a downloader that only saves pictures one by one does not need to read your data on any site, let alone all of them. The broad permission is about packaging and converting, not about downloading.
How to judge an extension before installing it
- Read the install prompt. "Read your data on all websites" is a much larger grant than "read your data on the site you are on".
- Look at when it asks. A permission requested at the moment you use a feature is easier to evaluate than one taken at install time for something you may never use.
- Check the site access setting. In
chrome://extensions, open an extension's details and look at Site access. You can often restrict it to On click, which many extensions work fine with. - Ask what it does when you say no. A well-built tool degrades. A tool that refuses to work at all was probably not asking for the reason it gave.
- Read the privacy policy for specifics. "We respect your privacy" is not a claim. A list of exactly when the extension contacts the network is.
What we do, and what we do not
Pixcrate declares the broad pattern in its manifest, because image addresses cannot be known before you pick some, but it never requests it as a whole. At the moment you ask for a ZIP or a format change, it asks for the specific sites your chosen pictures come from, in one prompt, and nothing else. If you decline, those pictures still download one by one.
Ordinary downloading needs no host permission at all, so on the free tier the question
never arises. Scanning the page uses activeTab, which Chrome grants only for
the tab whose toolbar icon you clicked, and only after you click it. There is no
cross-tab feature, so there is nothing to read from your other tabs.
Our privacy policy lists the five situations in which the extension touches the network, and on the free tier opening it makes no network request at all.
You do not have to take that on faith. The install prompt, the Site access setting, and the permission prompt when it appears will each tell you the same thing, and they are harder to fake than a marketing sentence.
See also: how to download all the images on a page, and how to save a CSS background image.