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In-Browser Processing and Safe Data Handling

We will summarize the points to check when using web tools that are labeled as ``processing only within the browser'' or ``local processing.''

What In-Browser Processing Means

JavaScript loaded by the page performs the processing on your device and returns the result on screen or as a download. The browser can read only files that you explicitly select.

Each Develop Tools page explains how it handles input data. Features that require network access, such as clock checking, clearly state that exception on the page.

Before You Begin

  1. Make sure the page uses HTTPS on the official domain.
  2. Review the Privacy and Limitations sections at the bottom of the tool.
  3. Extract only the necessary parts of sensitive data before entering them.
  4. Visually check the processing results before saving or sharing them.

How Browser Storage Differs

Processing in the browser is different from storing data in the browser. Some tools use localStorage to retain display settings, but this does not mean that the entered code or selected files are stored. In private browsing mode, saved settings may be removed when the session ends.

Specific example: Confirmation before loading in-house images into the image conversion tool

When using online tools such as image conversion, CSV viewing, and code masking, do not rely solely on the explanation that ``processing is done within the browser.'' Instead, check the communication destination, saved content, and required permissions separately.

  1. Open a legitimate domain with HTTPS and check the tool's privacy statement.
  2. If you can use your browser's developer tools, use test data to check whether there is communication.
  3. Check whether the entered content remains even after the page is refreshed, and understand the storage range such as localStorage.
  4. Reduce and mask production data to the minimum required scope, then verify that no original information remains in the result.

In-browser processing may also result in communication for other functions such as page display, advertisements, time/IP confirmation, etc. Consider whether input data is sent or whether the page does not communicate at all.

Frequently asked questions

Do you want to read all files on your PC just by pressing the file selection button?
With the standard File API, a page can read only files selected by the user. If a feature requests folder access or additional permissions, verify the scope you are granting.
Is it always safe to work offline?
No network communication is one useful signal, but you must also consider where results are saved, whether the device is shared, and which browser extensions are installed.

Reference information