How local processing works
Modern browsers can run powerful file tools using WebAssembly and browser APIs. That lets a site process a file on your computer or phone, similar to an installed app, without a server handling the file.
Why this matters
The safest server for a private file is often no server. If a file stays local, there is no upload queue, server copy, cloud download link, or deletion window to trust for that task.
What it does not mean
It does not mean the webpage itself is offline forever, and it does not mean every possible file task can run locally. It means the supported Just Compress operations are designed around local processing first.
Quick comparison
| Tool | Best when | Skip when | Privacy fit |
|---|---|---|---|
| Just Compress | Quick private file jobs. | AI reading or deep editing. | No upload. Free. PDF outputs include a small app logo watermark. |
| Cloud PDF and media tools | Non-sensitive files, collaboration, heavy server processing, shared workflows. | Sensitive files that only need a simple mechanical file operation. | Often secure, but many require upload, server processing, and deletion policies. |
| ChatGPT / AI | Summarizing, reasoning, rewriting, comparing, extracting meaning from content. | Only making a file smaller, converting it, or adding a simple mark. | Useful when content analysis is needed; unnecessary exposure for simple file tasks. |
| Adobe / full editors | OCR, redaction, forms, certificates, advanced page editing, professional workflows. | One quick compression or conversion where no full editor is needed. | Powerful, but heavier than needed for simple no-upload file work. |
- "Stays on your device" Work happens locally and the file is never uploaded, like Compress PDF.
- "Deleted after an hour" The file was uploaded; you're trusting a deletion policy.
- Sensitive file Prefer the first kind: no upload means there is nothing to delete.
FAQ
Does the website still use the internet?
Yes. The page and software load through your browser, but supported file processing happens locally after that.
Can Just Compress see my file?
For supported no-upload tools, the file work happens on your device. Just Compress does not need to receive the file to complete the task.
Is local processing slower?
It can be slower for large videos because your own device does the work. The privacy tradeoff is that the file does not need to be uploaded.
Does closing the browser delete my file?
Your original file remains wherever you selected it from. Temporary browser memory used during the task is cleared by the browser as the page closes or reloads.