Text Diff Checker

What a diff checker is for

A diff checker lines up two blocks of text and shows you exactly what changed between them — which lines were added, which were removed, and which stayed the same. Instead of squinting back and forth between two versions trying to spot the one word that moved, you get a color-coded, line-by-line comparison that points straight at the difference.

When you'd actually use it

Developers reach for this when comparing two versions of a config file, a function, or a log to see what a change touched. But it's just as handy outside of code: comparing two drafts of an email or contract to catch an edited clause, checking what a copy editor changed in an article, spotting the difference between two lists of names, or confirming that a pasted block really matches the original. Anytime you have a "before" and an "after" and need to know precisely what moved, a diff saves you from missing a small but important edit.

How the comparison works

The tool compares the two texts one line at a time. A line that exists only in the second block is marked as added, a line that exists only in the first is marked as removed, and unchanged lines are shown for context. A useful gotcha to know: most diffs are line-based, so if two lines differ by even a single character — a trailing space, a changed comma, a different capital letter — the whole line reads as changed. That's a feature, not a bug: it means nothing slips past you. Trailing whitespace and blank lines count too, so if lines look identical but flag as different, check for invisible spaces at the end.

How to use it

1. Paste your original text into the first box (the "before" version).
2. Paste the text you want to compare into the second box (the "after" version).
3. Run the comparison to see the two side by side, with added lines and removed lines highlighted.
4. Scroll through the highlighted results to review each change, then edit either box and compare again to check your fix.

FAQ

Does it compare word by word or line by line?

Line by line. If a single word on a line changes, that entire line is flagged as different so you never miss an edit.

Is my text private?

Yes. The comparison runs entirely inside your browser — nothing you paste is uploaded or stored anywhere.

Why do two lines that look the same show as different?

Usually invisible characters: a trailing space, a tab versus spaces, or different line endings. Trim the ends of the lines and compare again.

Is it free?

Yes, it's completely free and supported by ads on the page.