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Text Diff Checker
Compare two blocks of text line by line and see what changed — additions in green, removals in red — instantly in your browser.
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Quick Answer
Paste an original and a changed text and the tool compares them line by line, marking unchanged lines plainly, removed lines in red and added lines in green. It compares by position — line one against line one, line two against line two — which is simple and clear, but means inserting a line near the top can show everything below it as changed. Everything runs in your browser; nothing is uploaded.
What the Text Diff Checker Does
This tool shows the differences between two versions of a text. It lines them up and marks each line as unchanged, removed or added, so you can see at a glance what was edited between the original and the changed version.
It is the quick way to spot edits between two drafts, two configs or two snippets — what was taken out, what was put in, and what stayed the same.
How It Works
The tool splits both texts into lines and compares them position by position: the first line of the original against the first line of the changed text, the second against the second, and so on. Where two lines match, the line is shown unchanged; where they differ, the original line is marked as removed and the changed line as added.
This positional approach is simple and easy to read, but it is not the kind of diff that git or most diff tools use. Those use the Myers algorithm, which finds the longest common subsequence so that inserting or deleting a line is recognised as a single change. Here, an insertion near the top shifts every line below it out of alignment, so they all show as changed.
What it checks & how
- Split into lines. Break both the original and the changed text into lines.
- Compare by position. Line up the two and compare line one to line one, line two to line two, and so on.
- Mark each line. Show matching lines plainly; mark a differing original line as removed and the changed line as added.
- Show the result. Display the marked-up comparison, removals in red and additions in green.
How it compares
for each line position i:
original[i] == changed[i] → unchanged
original[i] != changed[i] → - original[i] (removed) and + changed[i] (added)Worked example
apple / banana / cherry vs apple / BANANA / cherry → line 2: - banana + BANANA (lines 1 and 3 unchanged)Because it compares by position, inserting a line near the top pushes the following lines out of alignment, so they all show as changed. A Myers or longest-common-subsequence diff would recognise the single insertion.
Standards & references
- Positional line comparison — The two texts are compared line by line at the same positions. It is simple and predictable, and works well when edits happen in place without adding or removing lines.
- Not a Myers / LCS diff — git, GNU diff and most diff tools use the Myers algorithm (Eugene Myers, 1986), based on the longest common subsequence, which treats an inserted or deleted line as one change. This tool does not, so inserts and deletes shift the alignment.
- Line granularity — Differences are shown at the whole-line level — a changed line appears as a removed line plus an added line. There is no word-level or character-level highlighting within a line.
Accuracy & Limitations
For in-place edits — where lines are changed but none are added or removed — the comparison is accurate and clear: the changed lines are flagged and the rest shown as unchanged.
For insertions and deletions it can mislead. Because it compares by position, adding or removing a line near the top shifts everything below out of alignment, so many unchanged lines are reported as changed. A Myers or longest-common-subsequence diff would handle this correctly.
It works at the line level, not within a line. A line with a one-word edit is shown as a whole removed line plus a whole added line, with no highlighting of the specific word that changed.
It is case-sensitive and exact. A difference in capitalisation, spacing or punctuation makes two lines count as different, which is precise but means trivial formatting changes show up as edits.
Real-World Use Cases
Comparing two drafts
See what changed between two versions of a text.
Checking config edits
Spot changed lines between two configurations.
Reviewing a snippet
Find the edits between two versions of code or text.
Proofreading changes
Confirm exactly which lines were altered.
When to use it — and when not to
Good for
- Comparing two texts line by line
- Spotting in-place line edits
- A quick, readable change view
- Checking config or draft changes
Not the best choice for
- Texts with inserted or deleted lines
- Word-level or character-level diffs
- Large files needing an exact diff
- Merging or three-way comparison
For inserts and deletes, or word-level changes, a tool using the Myers / longest-common-subsequence algorithm — like git diff or a dedicated diff app — aligns the texts correctly. This tool is a simple positional line comparison.
Frequently Asked Questions
How does it compare the two texts?
Line by line, by position: the first line of the original against the first line of the changed text, the second against the second, and so on. Matching lines are shown plainly; differing lines are marked as removed and added.
Why does it show every line as changed after I add a line?
Because it compares by position. Inserting a line near the top shifts every line below it down by one, so each no longer matches the line at the same position and all show as changed. A Myers or longest-common-subsequence diff would recognise the single insertion.
Is this the same diff git uses?
No. git and most diff tools use the Myers algorithm (1986), based on the longest common subsequence, which treats an inserted or deleted line as one change. This tool uses a simpler positional line comparison.
Does it highlight the exact word that changed?
No. It works at the whole-line level, so a changed line appears as a removed line plus an added line. There is no word-level or character-level highlighting within a line.
When is the comparison most accurate?
When edits happen in place — lines are changed but none are added or removed. Then the changed lines are flagged correctly and the rest shown as unchanged.
Is it case-sensitive?
Yes. A difference in capitalisation, spacing or punctuation makes two lines count as different. The comparison is exact, so even small formatting changes show up.
What do the colours mean?
Removed lines from the original are shown in red with a minus, and added lines from the changed text in green with a plus. Lines that match are shown plainly as unchanged.
Can it compare more than two texts?
No. It compares exactly two — an original and a changed version. For a three-way comparison or a merge, a dedicated diff or merge tool is needed.
Does it work for code as well as prose?
Yes, for in-place line edits. But code edits often add or remove lines, where the positional comparison shifts out of alignment, so a Myers-based diff is better for code with insertions.
Why are two visually identical lines marked as different?
Usually a hidden difference — a trailing space, a tab versus spaces, or different punctuation. The comparison is exact, so any character difference counts.
Is my text uploaded?
No. The comparison runs entirely in your browser. Nothing is sent to a server, so both texts stay on your device.
How can I get a more accurate diff?
Use a tool built on the Myers or longest-common-subsequence algorithm, such as git diff or a dedicated diff application. Those align the texts so inserts and deletes are recognised as single changes.
References
Compares the two texts line by line, by position; a simple positional diff, not the Myers or longest-common-subsequence algorithm that git and most diff tools use.
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