Free Diff Checker Online
Compare two blocks of text and highlight the differences line by line. Instantly see which lines were added, removed, or unchanged between two versions.
Comparing two versions of a document — to see what changed between a first draft and a revision, to review what a config change actually modifies, or to check that two files that should be identical really are — is a fundamental task in software and writing. This diff checker compares two blocks of text line by line and highlights the differences: lines only in the first version are shown as deletions (red), lines only in the second are shown as additions (green), and lines in both are shown unchanged. The comparison happens entirely in your browser.
Diff Checker
How to use this diff checker
- Paste the original text in the left panel.
- Paste the modified text in the right panel.
- Click Compare to compute the diff.
- Red lines exist only in the original; green lines exist only in the modified version; unmarked lines are unchanged.
Common use cases
- Reviewing what changed between two versions of a configuration file before deploying
- Comparing a draft document to a revised version to see which sentences were added or removed
- Checking that two files that were supposed to be synced are actually identical
- Spotting unintended changes after a search-and-replace operation
- Auditing a generated file against a hand-written reference
Frequently asked questions
Is this a line-by-line or character-by-character diff?
Line-by-line. A line is shown as added if it appears in the second input but not the first, and as removed if it appears in the first but not the second.
Does whitespace affect the diff?
Yes by default — a line with a trailing space differs from the same line without one. Normalize whitespace first if your files may differ only in indentation or line endings.
What algorithm does this use?
A longest-common-subsequence (LCS) algorithm, the same approach used by the Unix diff command. It finds the minimum set of insertions and deletions needed to transform the original into the modified version.
Can I diff code files?
Yes — the tool is plain-text, so it works on source code, JSON, YAML, SQL, or any other text format. For large multi-file reviews, a dedicated tool like git diff is more efficient.