Text Diff Checker
Paste an earlier version on the left and a later one on the right, press Compare, and see every line marked as added, removed or unchanged, with a count of each. The comparison works line by line and is case- and space-sensitive, so one changed word shows as a removed line plus an added line. Free, no sign-up, and nothing is uploaded.
How to Use the Text Diff Checker
- Paste the original. The older or reference version goes in the left box.
- Paste the revised text. The newer version goes in the right box. Put each sentence you want compared on its own line (see below).
- Press Compare. Editing either box clears the result, so press the button again after changing anything. Clear empties both boxes.
- Read the output. Green lines marked + exist only in the revised text; red, struck-through lines marked − exist only in the original; plain lines are in both. Three counters give lines added, lines removed and lines unchanged.
How the Comparison Works
The checker splits each text at line breaks and finds the longest sequence of identical lines that appears in both, in the same order. Everything in that sequence is unchanged. Any other line in the original is removed, and any other line in the revised text is added. This is the same longest-common-subsequence idea behind the Unix diff command. Matching is exact: a different capital letter, an extra space at the end of a line or a changed punctuation mark makes two lines different.
Prose needs one sentence per line
Because the unit is a line, a paragraph typed as one long line is either identical or entirely replaced — one changed word shows as the whole paragraph removed and the whole paragraph added. Put a line break after each sentence in both boxes first and the diff shows the sentences that really changed. It never marks changes inside a line.
Worked Example
Two versions of a three-line note. The revision rewords the second line and adds a fourth:
Original
Sleep helps memory. Students should sleep eight hours. Caffeine does not replace sleep.
Revised
Sleep helps memory. Students should sleep seven to nine hours. Caffeine does not replace sleep. Naps can help.
Result
Unchanged: 2. Removed: 1 (Students should sleep eight hours.). Added: 2 (Students should sleep seven to nine hours.; Naps can help.)
The reworded line appears twice, once struck through and once added, because the tool cannot tell an edit from a deletion plus an insertion. For a whole paragraph in one line it would be 1 removed and 1 added with nothing unchanged.
What It Is Good For — and What It Is Not
- Good for: comparing two drafts of an essay (one sentence per line), two versions of a reference list, two copies of a list or a configuration, or a text before and after cleaning.
- Not word-level. It does not highlight the changed words inside a changed line. Split the lines further if you need that precision.
- Case and spacing count. Introduction and introduction differ, and so do word and word followed by a trailing space. Strip stray spaces first if you want them ignored.
- Not a similarity or paraphrase measure. It tells you what differs, not how close two texts are in wording. For that, use the Paraphrase Checker.
- Large inputs. The method compares every line of one text with every line of the other, so very long documents (many thousands of lines) can make your browser slow.
Which Tool Do You Need?
| If you want to… | Use |
|---|---|
| See which lines changed between two versions | This Text Diff Checker |
| Measure how much a paraphrase echoes its source | Paraphrase Checker |
| Compare two lists of items as sets (common, only in A, only in B) | Compare Lists |
| Count words in each version | Word Counter |
Frequently Asked Questions
- How does the text diff checker work?
- It splits both texts into lines, finds the longest run of identical lines they share in the same order, and marks everything else as added (only in the revised text) or removed (only in the original). It reports the three counts.
- Can I use it to compare essay drafts?
- Yes, if you put one sentence on each line in both boxes. If each paragraph is a single line, any change inside it shows as the whole paragraph removed and re-added.
- Is the comparison case-sensitive?
- Yes, and it is space-sensitive too. Introduction and introduction are different lines, and so are two lines that differ only by a trailing space.
- Why does one changed word show as two lines?
- Because the comparison works by line. A line that has changed is no longer identical to anything in the other text, so the old line counts as removed and the new one as added.
- What do the colours mean?
- Green lines with + exist only in the revised text. Red struck-through lines with − exist only in the original. Grey lines are the same in both.
- Is this the same as the Paraphrase Checker?
- No. The diff checker marks exact line differences between two versions. The Paraphrase Checker scores how many words and phrases a paraphrase shares with a source passage.
- Is my text uploaded?
- No. The comparison runs in your browser and nothing is sent to a server.