What is a diff checker?
A diff checker compares two versions of text and highlights the differences between them — additions, deletions, and modifications. It's essential for code review, document comparison, and change tracking. This tool runs entirely in your browser using a line-by-line diff algorithm.
How a diff checker works
A diff checker compares two blocks of text and highlights exactly what changed — which lines were added, removed, or modified. Instead of reading both versions and hunting for differences by eye, you see them marked side by side, which is how code review, document comparison, and change tracking are done in practice.
The comparison is line-based: each line in the original is matched against the revised text, and the tool shows insertions and deletions so the smallest edit is easy to spot in a large file.
Common uses
Compare two versions of a config file to see what a deployment changed, check what edits a collaborator made to a document, or verify that a copy-pasted block matches the original. Swapping the two sides lets you view the change from either direction, which helps when you are trying to understand who changed what.
Reading a diff
Read a diff as instructions to turn the original into the revised text: removed lines are what to take out, added lines are what to put in, and unchanged lines give context. Focusing on only the marked lines lets you review a large change in a fraction of the time.
How to compare two texts
- 1Paste both versions. Put the original text on one side and the revised text on the other.
- 2Click Compare. Added, removed, and changed lines are highlighted between the two.
- 3Swap if needed. Use Swap to reverse the two sides and view the difference from the other direction.
Examples
A changed line
Input
Original: color: red Revised: color: blue
Output
- color: red + color: blue
An added line
Input
Original: a b Revised: a b c
Output
a b + c
Diff markers
How changes are shown.
| Marker | Meaning |
|---|---|
| + (added) | Line present only in the revised text |
| - (removed) | Line present only in the original |
| unchanged | Line identical in both |
| modified | Line present in both but different |
Frequently asked questions
What kind of differences does it detect?+
Line-level additions, deletions, and modifications between two texts, highlighted so you can see exactly what changed.
Can I compare code as well as prose?+
Yes. Any plain text works — source code, config files, logs, or documents. The comparison is based on lines, which suits code well.
What does Swap do?+
It reverses which text is treated as the original and which as the revised, so you can view the same change from the opposite direction.
Is there a size limit?+
Because comparison runs in your browser, you are limited only by your device's memory, so large files compare without an upload.
Is my text private?+
Yes. Both inputs stay in your browser and are never sent to a server.
Is it free?+
Yes — free with no limits.
Does it detect moved lines?+
A line that moved appears as a removal in its old place and an addition in its new one, because the comparison is position-based.