Free Text Diff Checker – Compare Two Texts

Text Diff Checker

See which lines were added or removed between two text versions — free, private.

Original text

Changed text

Finding What Actually Changed Between Two Versions

Scrolling through two versions of a contract or a config file looking for differences by eye is slow and error-prone — the human eye is bad at spotting a single changed word buried in an otherwise identical paragraph. This tool compares two blocks of text line by line and highlights exactly what was added, removed, or changed.

The Comparison Method

The tool runs a longest-common-subsequence (LCS) based line-matching algorithm, the same family of approach used by tools like Git's diff — it identifies the longest stretch of unchanged lines shared between both versions, then marks everything outside that shared sequence as an addition or removal. This is more reliable than a naive line-by-line position comparison, since it correctly tracks a moved or inserted line rather than falsely flagging every line after an insertion point as "changed."

A Worked Example

Compare a 20-line configuration file where one new setting was added on line 8 and one old setting was removed on line 15. A naive comparison tool would flag every line from 8 onward as different, since everything shifted position. The LCS-based approach here correctly identifies just those two actual changes — one addition, one removal — and shows the other 18 lines as unchanged, which is the difference between a genuinely useful diff and a noisy one.

Where People Rely On This

Developers comparing two versions of a code snippet or config file without pulling up a full Git client. Writers and editors tracking what changed between draft two and draft three of an article. Legal and contract reviewers spotting exactly which clause was modified between a sent draft and a returned redline. Students comparing their own essay draft against a previous version to see what an editing pass actually changed.

Reading the Highlighted Output

Added lines and removed lines are marked with distinct visual treatment so you can scan quickly rather than reading every line in full — this matters most on longer documents, where the goal is spotting the handful of real changes among hundreds of unchanged lines. For documents with heavy internal repetition (like similar boilerplate clauses), reviewing flagged sections in context rather than in isolation avoids misreading a coincidental match as an actual change.

What This Doesn't Catch

Line-level diffing flags a line as changed if any character within it differs — it won't highlight the specific word that changed inside a long, otherwise-identical line, only that the line as a whole differs. For fine-grained word-level comparison within a single sentence, you'd need a word-diff tool rather than this line-based approach, which is optimized for structured content like code, configs, and lists rather than flowing prose.

Handled Entirely On Your Device

Both text blocks are compared using client-side JavaScript in your browser — this matters for anyone comparing confidential documents like contracts, source code, or personal drafts that shouldn't be sent to a third-party server just to spot the differences.

Does this compare word-by-word or line-by-line?

Line-by-line — it identifies which entire lines were added, removed, or match between the two versions, rather than highlighting individual changed words within a line.

Why does a single small edit sometimes show two lines as changed instead of one?

If your edit added a line break or merged two lines, the algorithm correctly interprets that as a structural change (a removal plus an addition) rather than a modification of one line, since the line boundaries themselves shifted.

Can I compare code files with this, or is it just for plain text?

It works well for code, configuration files, and any structured text, since the line-based LCS comparison doesn't depend on the content being prose.

Does whitespace-only changes (like extra spaces) get flagged as a difference?

Yes, by default any character difference including whitespace triggers a line being marked as changed, since trailing or extra spaces are sometimes meaningful in code and configs.

Is there a size limit on the two texts I can compare?

There's no fixed limit, though comparing very large documents (thousands of lines) will take proportionally longer since the comparison runs on your device's processor.

Diff Checker vs. Manually Reading Both Versions

For a two-line change in a ten-line document, reading both versions side by side works fine. For a two-line change buried in a two-hundred-line document, manual comparison becomes genuinely unreliable — the eye tires and starts skimming, which is precisely when a small but important change gets missed. Automated line matching doesn't tire, which is the entire value proposition once documents grow past a page or two.

A Second Example

Comparing two versions of a Terms of Service document where a single sentence about data retention was quietly added on line 340 of 400. A quick visual skim of both documents side-by-side would very plausibly miss that one sentence; the line-matching diff flags it immediately as the sole addition, which is exactly the kind of change a reader would want called out explicitly rather than buried.