Text Diff Checker

What Is a Text Diff?

A "diff" (short for difference) compares two versions of text and identifies exactly which lines were added, removed, or unchanged between them. This concept originates from software version control (the Unix diff command dates back to the 1970s) but is broadly useful anywhere you need to compare two versions of a document, list, or piece of content and quickly spot what changed, rather than re-reading both versions line by line.

How to Read the Diff Output

Lines highlighted in green appear in the "Changed Text" box but not in the "Original Text" box — these are additions. Lines highlighted in red appear in the original but not in the changed version — these are removals. Lines with no highlighting are unchanged and appear identically in both versions. A line that was edited (rather than purely added or removed) typically shows up as one red line (the old version) followed by one green line (the new version), since the algorithm treats a modified line as a removal-plus-addition pair.

Common Uses for Text Comparison

Writers and editors use diff checking to review changes between draft versions of an article or document. Developers use it constantly to review code changes before merging (this is the core function behind every pull request review in tools like GitHub). Legal and contract professionals use diffing to spot exactly what changed between contract revisions — a critical task where a single altered clause can have major consequences. Students and researchers use it to compare citation lists or check for accidental duplication across document versions.

Frequently Asked Questions

Does this compare word-by-word or line-by-line?

This tool compares line by line — the standard approach for most diff tools, and the most useful granularity for documents, code, and lists. If a single line has a small change, the whole line is flagged rather than just the altered word.

Does whitespace matter in the comparison?

Yes — this tool performs an exact comparison, so trailing spaces or different indentation will cause two visually similar lines to be flagged as different. If this creates noise in your comparison, consider trimming both texts consistently before pasting.

Can I compare very long documents?

Yes, though for very large documents (thousands of lines), consider comparing section by section for easier review, since a diff with hundreds of changes can be harder to scan visually even when technically accurate.