Privacy
Client-Side vs Server-Side PDF Tools: How Browser PDF Tools Work
By SnapPDF · 6 min read
You may have noticed that some PDF websites say your files never leave your device. That is the idea behind client-side processing. This article explains the difference between client-side and server-side tools in plain language, and what it means for your privacy and speed.
Server-side tools
A server-side tool sends your file to a computer owned by the website. The server does the work, then sends the finished file back. This is how most traditional online converters operate. It means your upload speed matters, large files take longer, and a copy of your file exists on someone else's machine.
Client-side tools
A client-side tool downloads its code to your browser and uses your own computer to do the work. Modern browsers are powerful enough to read, merge, split, rotate and draw on PDFs using JavaScript libraries. Your document is opened in memory on your device and the result is saved directly to your downloads.
Benefits of client-side processing
- Privacy: the file does not need to be uploaded.
- Speed: no waiting to upload or download large files.
- Works with fewer limits: there is no server cost per file, so tools can be free without file caps.
- Fewer accounts: there is nothing to store on a server, so no need to sign up.
Limits to be aware of
- Very large PDFs depend on your device's memory.
- Older phones may be slower with big documents.
- Some heavy tasks, such as advanced OCR on scanned pages, are harder to run locally.
How SnapPDF does it
SnapPDF is built with open web technology. It uses libraries such as pdf-lib and PDF.js to read and change PDFs, and jsPDF to create them, all running inside your browser tab. When you close the tab, the data in memory is gone.
How to check for yourself
Open your browser's developer tools, switch to the Network tab and use a tool. If the page does not send your document to a server, the work is being done locally.
For practical advice on choosing tools, read our privacy checklist for online PDF tools.
Frequently asked questions
What does client-side mean?
It means the work happens on your own device, in your browser, instead of on a company's server.
Is client-side processing slower?
Usually it is faster, because you do not upload or download large files. Very large files depend on your device.
Which libraries does SnapPDF use?
SnapPDF uses pdf-lib, PDF.js and jsPDF, running in your browser.