File Diff Checker

How the comparison works

The tool compares the two texts line by line in a single pass. A line is reported as modified when the content at the same position differs on both sides. There is no view mode to pick: the side-by-side table is the result.

• Grey rows are lines that match on both sides.
• Green rows are lines present only in the modified text.
• Red rows are lines present only in the original text.
• Amber rows are lines that exist in both texts but differ.

Because the comparison is positional, inserting a block of lines shifts everything below it, and those lines are reported as changed.

Ignoring what doesn’t matter

The tool offers two toggles to keep the comparison focused:

• Ignore whitespace, formatting-only changes won’t appear.
• Ignore case, useful for SQL keywords or configuration keys.

Algorithm

The comparison runs in a single pass, so results appear near-instantly even for large files. It does not attempt to find a longest common subsequence the way git diff does; two files with content added at the top will report the rest of the file as modified.

Common uses

• Code review before opening a PR, to sanity-check what you actually changed.
• Config auditing between a staging and production environment file.
• Content proofing between a draft and a final article.
• License comparison when upstream dependencies ship new LICENSE files.
• Data reconciliation across two CSV exports from different systems.

Common mistakes

• Diffing two minified files. They are one line each, so everything is reported as “whole line changed”. Pretty-print both sides before pasting.
• Diffing files with different line endings. CRLF and LF are compared as exact characters, so every line shows as changed; normalize the line endings before pasting.
• Confusing whitespace-only diffs with logic changes. Use the “ignore whitespace” toggle when a teammate reformatted a file.