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Text Diff Checker

A diff checker to compare text: paste two versions and see exactly which lines were added, removed or left alone.

Loading Text Diff Checker…

Runs entirely in your browser. What you enter stays on your device — nothing is sent to a server. Verify it yourself

How does a text diff work?

It finds the longest common subsequence between the two texts — the same approach git uses — so it identifies which lines genuinely correspond. Comparing line by line in parallel would report everything after a single inserted line as changed.

Cost
Free, no limits
Upload
None — runs on your device
Sign-up
Not required
Works offline
Yes, once loaded

How to compare two texts

  1. Paste the original

    Put the earlier version in the left box.

  2. Paste the changed version

    Put the later version in the right box. Both stay in your browser.

  3. Adjust the comparison

    Turn on "ignore whitespace" if re-indentation is hiding the real change, or "ignore case" for prose where capitalisation is not the difference you are looking for.

  4. Read the result

    Added lines are green, removed lines red, with line numbers from both versions so you can find the change in the source.

Examples

  • Two drafts of a paragraphThe changed lines, marked as added or removed

    Faster than reading both and trying to spot the difference.

  • Two configuration filesExactly which settings differ

    The usual reason one environment behaves differently from another.

Key features of the Text Diff Checker

  • Line-by-line comparison with additions and removals marked
  • Works on any two blocks of text, not just code
  • Runs in the page — neither version is uploaded
  • Handles large blocks without a server round trip

What it compares

Input

  • Plain text, pasted
  • Up to 2,000 lines a side

Comparison

  • Line by line

Options

  • Ignore case
  • Ignore whitespace

When should you use this?

  • Checking what an editor changed in your draft.
  • Comparing two versions of a configuration or data file.
  • Verifying that a copy-paste actually matched the source.
  • Reviewing a contract revision against the previous version.

Limitations

  • The comparison is by line. A change to one word marks the whole line as changed, which is the standard behaviour but less precise than a word-level diff.
  • Reordered content shows as a removal and an addition rather than a move — the algorithm has no concept of a block moving.
  • Whitespace differences are real differences here. Trailing spaces and tab-versus-space changes will show up.
  • Very large inputs are limited by browser memory, since the comparison happens on your device.

Troubleshooting

Every line shows as different

Usually line endings (CRLF versus LF) or a change in indentation. Both alter every line even when the visible text is identical.

The page slows down on large inputs

The comparison runs on your device. Very large documents are bounded by browser memory; comparing the relevant sections separately is faster.

Common mistakes to avoid

  • Comparing a re-wrapped version against an unwrapped one and concluding everything changed. Wrapping alters the line boundaries the diff works on.
  • Assuming an unchanged diff means identical files. Invisible characters and encoding differences can survive a line-level comparison.

Pro tips

Tips for better results

  • Line endings

    Normalise line endings across operating systems first

    Normalise line endings before comparing files from different operating systems, or every line will show as changed.

  • Whole-file diffs

    If everything changed, suspect indentation or re-wrapping

    If the whole document appears changed, check for a difference in indentation or a re-wrapped paragraph — both alter every line.

Standards and terms behind the Text Diff Checker

The named things this tool works with, and the documents that define them.

Edit distanceHow it works
The number of insertions, deletions and substitutions between two texts; the basis of every diff view.
Character encodingHow it works
The mapping from bytes to letters; the wrong one turns accents and emoji into rubbish.

Also searched as: compare two documents, spot the difference between two texts, line by line comparison.

How the comparison works

The tool computes a longest common subsequence between the two texts — the same approach git diff uses. That matters: comparing the two line by line in parallel would report every line after a single inserted line as changed, which for a diff is not an approximation but the wrong answer.

Finding the longest common subsequence means the tool identifies which lines genuinely correspond between the two versions, so an insertion shows as one added line rather than shifting everything below it.

Ignore options

Ignore whitespace collapses runs of spaces and trims the ends of lines before comparing. Use it when re-indentation or a trailing space is hiding the real change.

Ignore case compares case-insensitively. Useful for prose where a capitalisation change is not the difference you are looking for.

Both change what counts as "the same line", so the diff will look different with them on. The displayed text is always the original, with its original casing and spacing.

Size limit

The comparison is capped at 2,000 lines per side. The algorithm builds a table proportional to the two lengths multiplied together, and past that point the browser tab would lock up rather than finish. If you are comparing something larger, a command-line diff is the right tool.

Privacy

The Text Diff Checker runs entirely in your browser. What you enter and the result it produces stay on your own device — nothing is sent anywhere, because nothing needs to be.

You can confirm this rather than take our word for it: open your browser’s developer tools, watch the Network tab, and use the tool. No request carries your input. It also keeps working with the connection off.

Details are in the privacy policy.

More text tools

What next?

Word and character counts for either version.

Count what changed

Text Diff Checker — questions

How does this compare two texts?

With a longest-common-subsequence algorithm — the same family of approach that git diff uses. It identifies which lines genuinely correspond, so inserting one line does not mark everything after it as changed.

Can I compare code?

Yes. The comparison is line-based and format-agnostic, so code, JSON, configuration files and prose all work. Turn on "ignore whitespace" if re-indentation is obscuring the real changes.

Why is there a 2,000-line limit?

The algorithm needs a table proportional to the length of both texts multiplied together. Past a few thousand lines that becomes slow enough to freeze the browser tab, so the tool declines rather than hanging.

Are my texts uploaded?

No. The comparison runs entirely in your browser — useful when you are diffing something you would rather not paste into a website.

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