Diff Checker

How to read the comparison

The tool compares your two texts line by line and works out the smallest set of changes that turns one into the other.

Side-by-side view puts the original on the left and the changed version on the right, with corresponding lines kept level. Removed lines are marked on the left, added lines on the right. This view is easiest when you want to see both versions in context.

Unified view shows a single column in the style of git diff: lines starting with - were removed, lines starting with + were added, and unmarked lines are unchanged. This is more compact, easier to copy and paste elsewhere, and it's what's used on narrow screens where two columns won't fit.

A short summary above the output tells you how many lines were added, removed, and left alone — or confirms plainly that the two texts are identical, which is often exactly what you needed to know.

Comparison options

Three options change what counts as a difference.

• Ignore leading and trailing whitespace treats lines that differ only in indentation or trailing spaces as identical. Useful when comparing code that's been reformatted, or text copied from sources that handle spacing differently.
• Ignore case treats uppercase and lowercase as the same. Useful for comparing content where capitalisation isn't meaningful.
• Ignore blank lines skips empty lines entirely, so a version with extra spacing between paragraphs doesn't show up as a wall of changes.

Each option re-runs the comparison immediately, so you can toggle them to see which differences are substantive and which are just formatting.

What people use a diff checker for

• Comparing document drafts — see exactly what an editor or colleague changed between two versions of a document, without reading both in full.
• Reviewing code changes outside of a git workflow — comparing a file before and after an edit, or checking what differs between two configuration files.
• Checking configuration files — spotting the one changed setting between a working config and a broken one is a classic use, and often much faster than reading both.
• Verifying copies — confirming that a file, list, or block of text really is identical to another, which the summary answers directly.
• Comparing exported data — checking what changed between two exports of the same dataset, particularly for line-based formats like CSV or logs.

How line-based comparison works

The comparison uses a longest-common-subsequence algorithm, which is the same general approach behind git diff and most other diff tools. It finds the longest sequence of lines that appears in both texts in the same order, treats those as unchanged, and marks everything else as added or removed.

The comparison works on whole lines first, then takes a second pass over lines that changed and highlights the specific words that differ within them. So a single altered word in a long sentence is picked out for you, rather than leaving you to compare two near-identical lines by eye. Where two lines are too dissimilar to be a modification of one another, they're shown as a straightforward removal and addition instead, since highlighting every word would be noise rather than help.

Frequently asked questions

Is my text sent to a server?

No. The comparison runs entirely in your browser. Nothing you paste is uploaded, logged, or stored.

How large a text can I compare?

There's no hard limit, but there are practical ones. Past 2,000 combined lines, live comparison pauses and you'll need to click Compare manually; extremely large or very dissimilar inputs can take a while, or occasionally fail to compute, since everything runs in your browser rather than on a server.

Does it highlight the specific words that changed?

Yes. After comparing line by line, the tool takes a second pass over changed lines and emphasises the individual words that differ. You can switch this off with the "highlight changed words" option if you prefer plain line-level output.

Why are some changed lines not word-highlighted?

When two lines are too different to be a modification of one another, they're treated as a separate removal and addition. Highlighting nearly every word in that case would obscure the real changes rather than reveal them.

Why do the two texts show as different when they look the same?

Usually invisible differences: trailing spaces, different indentation, or different line endings. Try the "ignore leading and trailing whitespace" option.

Can I compare files?

Paste the contents of each file into the two boxes. The tool works with any plain text — code, config, CSV, logs, or prose.

Is it free?

Yes, completely free with no sign-up.