Text Diff Checker
Compare two blocks of text and see exactly what changed. Runs in your browser — nothing is uploaded.
About Text Diff Checker
Text Diff Checker compares two versions of a text line by line and marks precisely what changed — additions in green, removals in red, unchanged lines left alone. Everything is computed in your browser, so contracts, code and drafts stay on your machine.
Reading two versions side by side and trying to spot the differences by eye is unreliable in a specific way: the mind skims familiar text and quietly fills in what it expects to see. A single altered number in a quotation, a negation removed from a clause, or one changed character in a configuration value will survive several careful readings. A diff finds them without depending on attention.
The comparison here is line-based and uses a longest-common-subsequence algorithm, which is the same approach behind version control diffs. Rather than comparing line one against line one, it finds the longest sequence of lines the two texts share and treats everything else as inserted or deleted. That is why adding a paragraph at the top does not mark the whole rest of the document as changed — the shared lines are still recognised as shared.
The practical limit worth knowing is that this class of algorithm needs time and memory proportional to the two lengths multiplied together. Two very large documents would be slow enough to freeze the tab, so the input is capped and tells you when you exceed it rather than appearing to hang.
How to compare two texts
- Paste the original version into the left box.
- Paste the changed version into the right box.
- Tick Ignore whitespace if indentation changes are noise for your purposes.
- Click Compare.
- Read the result — green lines were added, red lines were removed, and the line numbers on the left map back to each version.
Tips & common problems
Ignore whitespace when comparing code
Reformatting or re-indenting marks nearly every line as changed. Turning whitespace off isolates the edits that actually alter meaning.
A moved block shows as a delete plus an add
Line-based diffs have no concept of relocation, so a paragraph moved elsewhere appears twice — once removed, once added. That is expected, not an error.
Identical text is a useful answer too
When the tool reports no differences, that is a positive confirmation that two files match exactly — handy for checking a copy against an original.
Compare exports, not screenshots
To compare document versions, export both to plain text first. Comparing rendered output cannot show you the underlying change.
Frequently asked questions
Is my text uploaded anywhere?
No. The comparison runs entirely in your browser. That matters here, because the things people most often compare — contracts, legal drafts, source code — are exactly the things you would not want to upload.
Does it compare word by word or line by line?
Line by line. Any line that differs at all is shown as removed and re-added, which keeps the output readable for prose and code alike.
What does 'ignore whitespace' actually do?
It ignores leading and trailing spaces and tabs when deciding whether two lines match, so re-indented code is not reported as changed. Differences inside a line still count.
Is there a size limit?
Each side is limited to 2,000 lines. The algorithm's cost grows with both lengths multiplied together, so the cap keeps the page responsive rather than letting it freeze.
Can I compare two files instead of pasting?
Open each file, copy its contents and paste them in. This page works on text you paste, which keeps it fast and avoids handling your files at all.
Why is a moved paragraph shown twice?
Because a line-based diff has no notion of a move. It sees the lines gone from one place and present in another, so it reports a deletion and an insertion.