Diff Checker

About this diff checker

What diff algorithm does this use?

A line-based LCS (longest common subsequence) diff — the same principle tools like `diff` and `git diff` use. Lines decide what counts as added or removed; within a changed line, a second word-level pass highlights just the span that actually differs.

Why is only part of a changed line highlighted?

When a removed line and an added line are paired up as one change, a second word-level diff runs between just that pair and highlights the specific word(s) that differ — so "date" → "date fruit" highlights only "fruit", not the whole line. Lines with no clear counterpart (e.g. a run of 3 removals matched against 1 insertion) fall back to a plain whole-line highlight.

What does "Ignore whitespace" do?

Trims each line and collapses runs of internal whitespace to a single space before comparing — so re-indented code or trailing spaces don’t show up as changes. The original text is still shown untouched in the result.

What does "Ignore case" do?

Compares lines case-insensitively, so `Hello` and `hello` are treated as identical. The original casing is still shown in the result.

Side by side vs. Unified — which should I use?

Side by side shows two aligned columns, like a code review diff — good for wide screens where you want to see both versions at once. Unified shows one column with +/− markers, like `git diff` — more compact and the better choice on narrow screens or for copying as plain text.

Is there a size limit?

Yes — 2,000 lines per side, since the LCS algorithm compares every line of one side against every line of the other and cost grows with the product of both lengths. A single very long line (over 400 tokens) skips the word-level highlight pass for the same reason, but still shows as a normal whole-line change.

Can I compare files directly instead of pasting?

"Load file…" (or dropping a file onto either box) reads it as text and fills that side — handy for XML, JSON, config files, or any other plain-text format. Files over 20MB are rejected with an error rather than freezing the tab.

Does this tool upload my data anywhere?

No. Both inputs — typed, pasted, or loaded from a file — are compared entirely in your browser. Nothing ever leaves your device.