What does a text diff checker do?
A diff checker compares two versions of a text line by line and shows exactly what changed: removed lines highlighted in red with a minus, added lines in green with a plus, unchanged lines left plain. Each line keeps its original line number from both versions, and a summary bar counts additions, removals and untouched lines — the same mental model as git diff, without needing the texts to live in a repository.
The comparison runs entirely in your browser. Neither text is uploaded, which matters more for diffs than for most tools: the things people compare — contracts, config files with credentials, unreleased copy — are often exactly the things that shouldn't touch a third-party server.
When to use it
Use it whenever two blobs of text should be identical but might not be: a config file on staging versus the one in the repo, an API response before and after a change, two versions of an email or legal paragraph a colleague edited, or a .env.example against a real environment file to spot missing keys.
It's also the quickest answer to "what did you change?" when someone hands you an edited document with tracking off. Paste the original on the left, the edited version on the right, hit Compare, and the changed lines are impossible to miss. Because the diff is line-based, it works best on text with meaningful line breaks — code, configs, CSVs, lists — rather than a single long paragraph, where any edit marks the whole line as changed.
Example
Paste yesterday's nginx.conf as the original and today's as the modified version. Compare shows client_max_body_size 10m; in red and client_max_body_size 100m; in green directly beneath it, with the surrounding lines untouched — a ten-second answer to why uploads suddenly started succeeding. The line numbers on the left tell you exactly where to look in the real file, and "Copy link to this result" produces a URL that reopens the tool with both texts and the computed diff, ready to drop into a chat thread.
How to use the Text Diff Checker with Line Numbers on Both Sides tool
- 1
Paste the original text
The left panel holds the baseline version you're comparing against.
- 2
Paste the modified text
The right panel holds the newer or edited version.
- 3
Hit Compare
Removed lines show in red, added lines in green, with line numbers from both versions and a change summary.
- 4
Share if needed
Copy a permalink that restores both texts and the diff for anyone who opens it.
Frequently asked questions
Are my texts uploaded to a server?
No. The diff algorithm runs entirely in your browser — both texts stay on your machine, which makes the tool safe for configs, contracts and other content you wouldn't paste into an online service that stores input.
Does it highlight changes within a line?
No — the comparison is line-based, like a classic unified diff. If one word changes in a line, the whole line shows as removed-plus-added. For prose, breaking the text into one sentence per line before comparing makes the output much more readable.
Is the comparison whitespace-sensitive?
Yes. Lines must match exactly, so a trailing space or a tab-versus-spaces difference makes otherwise identical lines show as changed. That's usually what you want when comparing configs, where invisible whitespace can be the actual bug.
How large a text can I compare?
The tool is comfortable with typical files — configs, source files, a few thousand lines. It uses a lightweight look-ahead matcher rather than a full diff algorithm, so on very large or heavily rearranged texts the pairing may be less minimal than git's output, though additions and removals are still correct.
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