Difference Checker

Spot the difference between two texts in seconds

Two documents that look identical to the eye almost never are. A line that was added or moved, a punctuation change, a date that was silently updated — these small differences matter a lot when you are reviewing a contract, accepting a code change, comparing two versions of a translation, or trying to figure out why a configuration file stopped working after "no changes". This Difference Checker compares two texts side by side and highlights every addition, deletion, and modification.

How to use the diff checker

Paste your first text (the "before") on the left and your second text (the "after") on the right. Click Compare. The tool aligns the two inputs and shows you exactly what changed: green for additions, red for removals, with unchanged content shown in normal weight for context. You can copy either version, or copy a clean version of the changes.

What the colours mean

A standard diff uses two basic markers: added content (lines or characters present in the new version but not the old) is highlighted in green, and removed content (lines or characters present in the old version but missing in the new) is highlighted in red. A "modified" line is technically a combination of both — the old version removed, the new version added — and is shown that way for accuracy.

Real-world uses

Contract and legal review. When a counter-party returns a contract draft "with minor edits", they usually mean dozens of small changes scattered through clauses you would never spot on a normal read-through. A diff makes every change instantly visible. This is the same principle redlining works on, without needing both parties to use Microsoft Word's tracked changes feature.

Code review. Developers see diffs in their IDE all day, but for a quick comparison of two snippets pasted from a chat message, a Stack Overflow answer, or two versions of a configuration file, an online diff is faster than spinning up a project.

Configuration file debugging. "It worked yesterday and now it doesn't" is almost always a config or environment change. Paste the old known-good config and the current broken one, and the diff will surface the one or two changed lines that broke things.

Translation QA. Bilingual editors compare a draft translation against an updated source text to find newly added or deleted sentences. The diff makes this fast even when the translated text is in a different script.

Document version control. Compare two drafts of a blog post, two versions of a press release, or two drafts of a meeting agenda. See exactly what was added, removed, or rewritten.

Data export comparison. Two CSV exports from the same database taken at different times — what records or columns changed? The diff will show you.

Tips for getting the most accurate diff

Normalise both texts the same way before comparing. If one version has Windows line endings (\r\n) and the other has Unix line endings (\n), the diff will show every single line as different, which is technically true but useless. Run both through a normalisation step first.

Trim trailing whitespace. Many editors silently add or remove trailing spaces, which produces a noisy diff with no real information value.

For very long documents, compare a section at a time. A diff over thousands of lines becomes harder to interpret because small unrelated changes mix with the real ones you care about.

For minor changes inside long lines, you may want a "word diff" instead of a line diff. The Difference Checker offers both, with character-level granularity for finely detailed comparison.

How the diff is computed

Behind the scenes, the tool runs a variant of the Myers diff algorithm — the same family of algorithms used by Git, Subversion, and most professional diff tools. It computes the shortest sequence of edits that turns one text into the other, then formats the result for display. This is more accurate than a naive line-by-line comparison because it correctly handles inserted or deleted lines without flagging everything below them as "different".

Privacy

Both texts are compared entirely in your browser. Nothing is uploaded or stored. That makes the tool safe for comparing confidential contracts, internal source code, proprietary configurations, and any other sensitive content. The text you paste is gone the moment you close the tab.