How this text diff checker works
A diff (short for "difference") is a comparison of two pieces of text that shows what changed from one to the other. This tool reads both versions as lists of lines and finds the longest sequence of lines they have in common — the Longest Common Subsequence. Those shared lines stay as context, while any line that exists only in the original is reported as a removal and any line that exists only in the changed text is reported as an addition.
Because the comparison is line based, a line that differs by even a single character shows up as one removed line followed by one added line. This keeps the result simple and predictable, and it is exactly how most version-control diffs present changes. The summary at the top counts the total additions and removals so you can gauge the size of a change at a glance.
apple / banana / cherry and the Changed text is apple / blueberry / cherry, the diff keeps apple and cherry unchanged, marks − banana as removed and + blueberry as added — a summary of 1 addition and 1 removal.| Symbol | Meaning |
|---|---|
| (space) | Unchanged line — present in both texts, shown for context. |
| + | Added line — present only in the Changed text (greenish). |
| − | Removed line — present only in the Original text (reddish). |
Reference note: the diff is computed with a classic dynamic-programming Longest Common Subsequence algorithm and runs entirely on your device. No text leaves your browser.
Frequently asked questions
- How do I compare two texts?
- Paste the first version into the Original box and the second into the Changed box, then press Compare. The tool lines up both texts and highlights every line that was added, removed or changed.
- What does a diff show?
- A diff shows the differences between two texts. Unchanged lines give context, removed lines are marked with a minus sign on a reddish background, and added lines are marked with a plus sign on a greenish background.
- How do I find what changed between two versions?
- Put the older version in Original and the newer one in Changed, then compare. The highlighted output and the additions/removals summary tell you exactly what changed.
- Does this compare line by line or word by word?
- Line by line. Each line is treated as a unit, so a line that differs by one character is reported as a removed line plus an added line rather than an in-line word change.
- Is my text uploaded anywhere?
- No — the comparison runs entirely in your browser. Your text is never sent to a server, stored or uploaded, so it is safe for private or sensitive content.
- Can I compare code?
- Yes. The diff works on plain lines of text, so it handles source code, config files, logs and prose alike. Paste both versions and the tool highlights the changed lines.