How this works in your browser
The comparison runs a diff algorithm over the two texts in your browser, treating each line as an atomic unit and finding the longest sequence of lines common to both. Everything outside that common sequence is classified as added or removed. Working at line granularity is what makes the output readable for code and structured documents, and it is equally why a single word changed in a long paragraph flags the whole paragraph: the line is the unit, so any change within it makes the line different. Nothing is transmitted, which is what makes this usable on contracts, legal drafts and internal documents.
Who uses Text Diff Checker
Reviewing document revisions
See exactly what changed between two drafts.
Checking contract amendments
Spot every alteration in a returned agreement without uploading it.
Comparing code or config
Find differences between two versions of a file.
Verifying a copy
Confirm two blocks of text are genuinely identical.
Frequently asked questions
Does it compare word-by-word or line-by-line?
Line-by-line. Each line is compared as a whole unit, which is the most common way to review document or code revisions.
Is my text uploaded anywhere?
No, the comparison algorithm runs entirely in your browser using JavaScript.
Can it handle very long documents?
Yes, though extremely large documents may take a moment longer to compute.
Why does changing one word mark the whole line as changed?
Because the comparison works on whole lines, which is the standard approach for reviewing revisions. It suits code and structured documents well. For prose written as long unbroken paragraphs it is less helpful, since a single edited word flags an entire paragraph. Breaking prose onto shorter lines before comparing gives a much more readable result.
Can I compare two documents rather than pasted text?
Open each file and paste its contents in. Because everything is compared locally, there is no size limit imposed by an upload, and confidential contracts or internal documents never leave your device.
Why do lines show as changed when they look identical?
Almost always invisible whitespace: a trailing space, a tab where the other has spaces, or different line endings from a file that has moved between Windows and Unix systems. Running both sides through the whitespace trimmer first usually clears the phantom differences.
Is this the same as version control?
It answers the same question for two blocks of text you have in front of you, but it keeps no history. Version control records every change over time with authorship; this is for the moment you have two versions and need to see what moved between them.