A browser-based tool is privacy-preserving when its code reads and processes the selected file on your device without transmitting the file. The browser File API permits local access after you choose a file, but the page's network behavior determines whether it remains local.
Local processing versus uploading
A file picker alone is not an upload. The browser's File API lets a web application access files that a user deliberately selects through a file input or drag-and-drop. The page can then read those bytes in memory and process them with JavaScript.
An upload is a separate action: page code packages some or all of the file into a network request and sends it to another system. A tool can therefore have a web address and still perform the actual work on the user's device.
Tools marked “Runs locally” process supported files in browser memory. Advertising, licensing, or analytics requests may still occur, but the selected document itself is not attached to those requests.
How to verify a local tool
You do not have to rely only on a privacy label. Modern browsers expose network activity through developer tools:
Open Developer Tools
Use the browser menu or the standard keyboard shortcut, then select the Network panel.
Clear previous requests
Clear the list immediately before choosing your test file so unrelated page-loading traffic is easier to separate.
Process a harmless test file
Complete the same steps you would normally use, watching for new POST, PUT, or file-sized requests.
Inspect suspicious requests
Check request payloads, destinations, and transferred sizes. Normal license or analytics traffic should not contain the selected file.
What local processing does not solve
Local processing reduces exposure to a tool provider's storage and server infrastructure, but it is not a complete security boundary. Consider the device, browser, extensions, downloaded output, and the document itself.
- A compromised device or malicious browser extension can still access sensitive information.
- The output may retain visible confidential content, annotations, attachments, or metadata that the chosen operation did not target.
- Very large files can exhaust browser memory or make a mobile device unresponsive.
- Workplace, legal, health, or financial records may be governed by policies that require an approved application even when processing is local.
A practical privacy checklist
- Confirm that the page explicitly says files are processed locally.
- Use a current browser on a trusted device.
- Test network behavior with a harmless file when the material is sensitive.
- Choose the narrowest tool needed for the task.
- Review the downloaded output before sharing it.
- Delete temporary downloads according to your organization's retention rules.
Try a local FreNiMi workflow
Frequently asked questions
Does selecting a file automatically upload it?
No. A browser can make a user-selected file available to page code without sending it over the network. Whether an upload occurs depends on what the page does afterward.
How can I check whether a tool uploads my file?
Open the browser developer tools, select the Network panel, clear existing entries, then use the tool and inspect any requests made while the file is processed.
Is local processing appropriate for every confidential file?
No. Follow your organization's data-handling rules, use a trusted and updated device, and avoid processing regulated files in an unapproved environment.
Primary reference
- MDN: Using files from web applications — how browsers expose user-selected files through the File API.