Diff Checker
Two drafts of a paragraph, two versions of a config, two clauses of a contract — when the question is "what exactly changed?", eyeballing two documents side by side is how mistakes slip through. This checker compares line by line using a longest-common-subsequence algorithm and lays the answer out as a unified view: removals marked −, additions marked +.
How to use it
- Paste the original text on the left and the revised text on the right.
- Press Compare.
- Read the unified result: − lines were removed, + lines were added, unmarked lines are unchanged. The summary counts all three.
Key facts
- Comparison is by whole line — the clearest granularity for prose, code and configuration.
- The summary totals added, removed and unchanged lines so you can gauge a change before reading it.
- The underlying algorithm is quadratic in the number of lines, which stays comfortable up to a few thousand lines per side.
About this tool
Two drafts of a paragraph, two versions of a config, two clauses of a contract — when the question is "what exactly changed?", eyeballing two documents side by side is how mistakes slip through. This checker compares line by line using a longest-common-subsequence algorithm and lays the answer out as a unified view: removals marked −, additions marked +.
The comparison runs in your browser, which is the whole point for sensitive material. Unreleased copy, internal configuration and legal drafts should not need a trip to a stranger's server just to be compared.
Like every TextKit tool, the Diff Checker runs entirely on your device. There is no account, no upload and no record of the content you process — close the tab and everything is gone.
Frequently asked questions
Why line-by-line instead of word-by-word highlighting?
Line-level output is calmer and more honest for most documents: you see the shape of the change at a glance, without the confetti of character-level highlighting inside every edited line.
What does it mean if everything shows as removed and added?
Usually that the line endings changed (for example CRLF pasted from Windows versus LF) or that every line was genuinely rewritten. Check the invisible characters first.
Is there a size limit?
Practically, a few thousand lines per side. The diff algorithm compares every line against every other, so truly huge files belong in a desktop diff tool.
Related tools
Word Counter
Words, characters, sentences and reading time — counted live as you type.
~/tool/case-converterCase Converter
Switch text between UPPERCASE, camelCase, snake_case and six more styles.
~/tool/lorem-ipsum-generatorLorem Ipsum Generator
Generate placeholder paragraphs, sentences or words for your layouts.