Can it ignore formatting differences?

Yes. Turn on "Ignore case" or "Ignore whitespace differences" to hide changes that only affect capitalisation or spacing.

What is the .diff download?

A unified diff, the standard patch format understood by git apply, patch and most code review tools.

No. The text is processed in your browser as you type and is never uploaded or stored.

JavaScript is turned off. InspireTools processes files in your browser, so the tools need JavaScript to run.

Compare two texts and highlight what was added, removed or changed.