Diff checker — offline

Diffing is something you do to the documents that matter most: two versions of a contract, a production config against a staging one, an environment file with real credentials in it, a legal clause someone edited without telling you. Pasting both halves into an online diff tool means uploading two complete copies of exactly the material you were being careful about.

The comparison here is computed by an open-source diff library running in your browser. Neither text is transmitted; the site has no backend, and a Content-Security-Policy blocks third-party requests. Load the page, go offline, and it still works.

Line mode compares whole lines and is the right choice for code, configs, CSVs, and logs — anything where a line is a meaningful unit and you want to see precisely which lines changed.

Word mode compares word by word, which is what you want for prose. When a single word changes in the middle of a long paragraph, line mode reports the entire paragraph as replaced and leaves you to find the difference by eye; word mode points at the word. For contract revisions and edited documentation it is the difference between a useful diff and a wall of red and green.

Additions appear in green, deletions in red with strikethrough, and unchanged text stays plain, all in one combined view rather than two columns you have to scan in parallel.

Most "unreadable" diffs are formatting noise rather than real change. Normalising both sides first fixes it, and every step stays on your device:

• Comparing JSON? Format both with the JSON formatter using the same indent, and enable Sort keys — otherwise reordered keys show up as changes when the data is identical.
• Comparing code? Run both through the code formatter first, so indentation and brace style stop dominating the result.
• Comparing lists? Sort and deduplicate both sides when order is not meaningful.
• Comparing SQL? Format both queries to a consistent layout first.

Comparing two PDFs rather than two texts? Extract the text from each and diff the results — also entirely on your device.