File selection does not automatically upload
Choosing a file gives page JavaScript permission to read that file in the browser. The code can inspect bytes, draw pixels, calculate hashes, and create downloads without sending the file elsewhere.
An upload occurs only when code transmits the file or derived content through a network request, form submission, WebSocket, or similar channel.
The webpage still uses the network
HTML, CSS, JavaScript, icons, and other assets are downloaded from the site. Analytics, advertising, error reporting, or third-party libraries may create additional requests.
A precise privacy statement should separate local file processing from general website hosting and logs.
Verify with synthetic data
Open developer tools, clear the Network panel, choose a harmless test file containing a recognizable fake value, run the tool, and inspect every request. The test value should not appear in request bodies, URLs, or headers.
Repeat after major updates and test both success and error paths.
Understand browser limits
Large files can exhaust memory because many browser APIs read the complete file. A local tool may also support fewer formats or advanced features than a server application.
For sensitive files, local processing is one risk reduction measure, not a replacement for approved software, access controls, and review.
Final review checklist
- Processing path described clearly
- Network panel tested
- Third-party requests understood
- Large-file memory limits considered
- Sensitive workflow policy followed