How Shridha Tools works on your files without uploading them

When you merge a PDF, shrink a photo or sign a document on Shridha Tools, the file is not sent to a server. This post explains how that works and how you can check it, because a claim like "your files stay on your device" is only worth something if you can test it.

What happens to your file#

1. You pick a file. Your browser reads it into memory on your device.
2. The page's own code works on it there. PDFs are edited with a library called pdf-lib, and pages are drawn with pdf.js, the PDF reader that is built into Firefox. Photos are resized and compressed with the browser's built-in drawing surface, the canvas.
3. The result is made in memory too. When you press Download, the browser saves it from there to your device.

Nothing in that path needs a server, so we did not build one.

How to check it yourself#

Open your browser's developer tools (F12 on most computers) and go to the Network tab. Then use a tool on a file.

• You will see requests for the page, its scripts and its fonts, all from the Tools site itself.
• You will not see a request that carries your file or its contents. Nothing is uploaded when you press the button.

The code is written so that the only fetch calls in the site read a QR code image the page has just made on your device, to save it as a file.

What we do see#

Tools is delivered by Google Firebase Hosting. Like any web host, it handles standard request details such as your IP address, the time, the page you asked for and your browser type, and may keep them in routine logs. We do not use these logs to identify anyone. We add no analytics, no ads and no tracking tools of our own, and the site sets no cookies. Your theme choice and similar small settings, where used, stay in your browser.

The limits of working on your device#

Doing the work locally is a trade, and some of the costs are yours:

• Memory. Big files need a lot of memory. A very large photo, over about 50 megapixels, can fail on an older phone.
• Page limits. "Pages as pictures" in Compress PDF works up to 100 pages at a time. Split large files first.
• Compress PDF has two modes. "Keep text" repacks the file and often saves little. "Pages as pictures" can save a lot, but text can no longer be selected or searched, and links and form fields stop working. The tool says so and shows the new size before you download.
• Password-protected PDFs cannot be opened. Remove the password first.
• Photos lose camera details. Resized and compressed photos are redrawn, so details such as the location are not copied into the new file.

Why we built it this way#

Part of it is privacy: the safest place for a file is the one you already control. Part of it is cost. With no server handling your files, an idle tool costs almost nothing, and that is what lets us keep it free without ads. The next post covers that: why Shridha has no ads.