Repeat the observation with a harmless sample

Open the tool first and let its scripts and other resources load. In the browser Network panel, enable preservation of the log if you need to compare several actions, then clear the visible requests. Select a non-sensitive test image with a recognisable filename and run one operation. Note whether a request appears when selecting, processing or downloading the file.

Inspect the method, destination and request payload of any new request. A GET for a processing library differs from a POST carrying file bytes, though methods alone are not proof of content. A blob download normally refers to data held by the browser and does not itself establish that no earlier transfer occurred. Repeat on the specific tool and mode you intend to use; evidence from an image resize does not cover an unrelated remote MCP action. This observation helps evaluate that run, while the source code and request details provide the stronger explanation.

Separate page loading from file handling

Every website must load something: HTML, JavaScript, CSS, images, fonts, ads, or badges. Those requests are different from a request that carries your selected file away after you choose it.

The useful question is narrower: did selecting and processing the file add a data-capable request that could contain the file?

Use the Network panel

Open developer tools, switch to the Network panel, and clear the request list immediately before processing. Run the tool, then inspect what appeared afterward.

Look especially for fetch, XMLHttpRequest, sendBeacon, form posts, or upload-like requests. A local result commonly appears as a blob URL created inside the current tab.

Understand the limit of the test

This is an observable browser check, not a formal security audit. It can show whether the processing action created visible upload-style traffic through common browser request paths.

That is still a strong practical signal. A tool that claims local processing should be willing to explain what it measures, what it does not measure, and which third-party hosts the page itself loads.