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Text Diff Checker

Spotting exactly what changed between two versions of a document is easy to get wrong when you read them side by side. This free text diff checker compares two texts and highlights the exact added and removed lines, so you can review edits, merge changes and catch mistakes in seconds.

Original

Changed

What is a Text Diff Checker?

A text diff checker, also called a text comparison tool, takes two versions of a piece of text and computes what changed between them. The word diff comes from “difference”. It aligns the two inputs line by line and marks each line as unchanged, added or removed, so you can see precisely where a document diverged.

Diffing is the engine behind version control, code review and collaborative editing. A good diff tool shows the added lines in one colour and the removed lines in another, so nothing is missed. This checker uses the classic longest-common-subsequence algorithm, which finds the minimal set of edits that turn one text into the other.

Editors use a diff to review a teammate’s rewrite, developers use it to check a config or data file changed exactly as intended, and writers use it to verify a co-writer’s edits. Because it runs in your browser, you can compare private or confidential text without uploading it anywhere.

How to use the Text Diff Checker

Paste the original text into the first box (A).
Paste the changed version into the second box (B).
Click Compare to run the diff.
Read the result: added lines are shown in green, removed lines in red, and unchanged lines keep a plain style.
Use the summary to see the number of additions and removals, then click Clear to start over.

Example

Text A: The sun is up

Text B (two lines): The sun is up
And the sky is blue

The checker aligns the two texts line by line. The first line is unchanged, and the second line is highlighted in green as added. The summary reports 1 addition and 0 removals, so you can see exactly which line was introduced.

Who is this Text Diff Checker for?

Spotting what changed in a document, config or data extract is a daily task in most teams. A diff tool makes the change obvious instead of fighting through it.

Developers: review an edit a teammate made to code, config or a data file before you merge it.
Writers and content creators: see exactly which lines a collaborator added or deleted in an article or script.
Marketers: compare two versions of ad copy or an email to confirm the only change was intentional.
Analysts: check that a dataset export matches the previous one line by line.

How the diff is reported

Comparing a short example (right column) against the original (left column) shows exactly how the tool labels each line.

Original	Changed version	Diff label
Hello World	Hello World	unchanged
foo bar	foo baz	changed
line three	line three	unchanged
(none)	fourth	added

Common use cases

Reviewing edits a colleague made to a document or article before you publish.
Comparing a template, config, or data file against a new corrected version.
Checking your own revision history when you no longer remember what you changed.
Merging contradictory drafts by seeing exactly which lines differ.

Pro tips

Paste both versions with identical line breaks so unrelated formatting changes do not swamp the real edits.
Read the summary count first — a huge difference means a formatting change, not a content change.
Use it to verify a find-and-replace behaved: it shows every touched line at a glance.
For very long texts, compare section by section to keep the highlighted changes readable.

FAQ

What is a text diff?

A text diff is the result of comparing two versions of a text to show what was added, removed or left unchanged between them.

How does the tool decide what changed?

It uses a longest-common-subsequence algorithm to align the two inputs and find the smallest set of edits that converts one into the other.

Does it compare word by word or line by line?

This checker compares line by line, which is ideal for reviewing paragraphs, config files and code where line structure matters.

What do the green and red highlights mean?

Green marks added lines and red marks removed lines. Unchanged lines stay in the default style.

Is my text uploaded anywhere?

No. The comparison runs entirely in your browser, so your text never leaves your device.

Can I compare very long texts?

Yes — paste as much as you need, though very large inputs are best split into sections to keep the highlights readable.

What is the longest common subsequence?

It is the longest sequence of lines or characters common to both texts, which the algorithm uses as the anchor to show everything else as an edit.

Is it free?

Yes, it is completely free and unlimited with no signup required.