What is the difference between a line diff and a word diff?

A line diff tells you which whole lines were added or removed. A word (or character) diff goes further and highlights exactly which words inside a changed line are different, so a one-word edit does not look like the entire line was rewritten. Diff Checker Pro does both at once — it aligns changed lines and then highlights the precise inline edits.

Can I compare two files instead of pasting text?

Yes. Each pane has a Load file button that reads a local text or code file directly into the browser. The file never leaves your machine — it is read with the browser FileReader API and compared locally.

What does the unified diff output look like?

It is the same format git and the patch command use — a header with both filenames, hunk markers, and lines prefixed with a space, a minus or a plus. You can copy it into a pull request description or save it as a .patch file and apply it with `git apply changes.patch`.

How do ignore-case and ignore-whitespace work?

Ignore-case compares letters without regard to upper or lower case, so Hello and hello are treated as equal. Ignore-whitespace collapses runs of spaces, tabs and newlines and trims each line, which is handy when only indentation or trailing spaces changed. Both options affect the highlighting and the exported patch.

Is there a size limit on what I can compare?

There is no hard limit, but because everything runs in your browser, very large inputs (tens of thousands of lines) will diff more slowly. For typical config files, code snippets, documents and JSON payloads it is effectively instant.

Completely. The whole tool runs client-side in your browser with no network calls. Your two versions, file contents and the generated patch are never uploaded, and your last comparison is remembered only in this browser via local storage.

Diff Checker Pro — Gera Tools

Diff Checker Pro compares two pieces of text and shows you exactly what changed — not just which lines differ, but which words or characters inside each changed line are new or removed. It is built for developers reviewing a code change, writers comparing two drafts, ops engineers checking a config file against a known-good version, and anyone who needs to spot the difference between two near-identical blobs of text. Paste both versions, or load local files, and the result updates instantly as you type.

Most simple “compare text” boxes only do a line-by-line diff: change one word and the whole line lights up red and green, leaving you to hunt for the actual edit. Diff Checker Pro aligns the changed lines first and then runs a second, finer diff inside each pair, so a single renamed variable or a fixed typo is highlighted precisely while the rest of the line stays neutral. You can switch between a side-by-side view (original on the left, changed on the right) and a unified view (the familiar plus/minus format used by Git), pick word-level or character-level inline highlighting, and toggle ignore-case and ignore-whitespace to filter out noise. When you are done you can copy a standard unified diff to paste into a pull request, or download it as a .patch file.

How it works

The tool runs a classic line diff to decide which lines were added, removed, kept or changed. Adjacent removed-and-added blocks are paired into modified rows, and for each pair it runs a second diff at the word or character level to produce the inline highlights. Added segments are shown in green, removed segments in red, and unchanged text is left plain. The ignore-case and ignore-whitespace toggles normalise the text before comparison — for example collapsing repeated spaces — so cosmetic differences do not drown out the real ones. The export uses the same unified-diff format that git diff and the patch utility produce, including a header with both labels and hunk markers, so the output is genuinely usable in a real workflow. Everything — parsing, diffing, highlighting and patch generation — happens in your browser; there are no network requests at any point.

Example

Suppose the original line is const total = price + tax and the changed line is const total = price + tax + shipping. A plain line diff would show the whole line as removed and re-added. Diff Checker Pro instead keeps const total = price + tax neutral and highlights only + shipping in green, so the review takes a second instead of a double-take.

Feature	Plain line diff	Diff Checker Pro
Whole-line add/remove	Yes	Yes
Word-level inline highlight	No	Yes
Character-level highlight	No	Yes
Side-by-side and unified views	Sometimes	Both
Export unified `.patch`	Rarely	Yes
Ignore case / whitespace	Rarely	Yes

Your last comparison is saved in this browser so it is still there when you come back, and nothing you paste or load is ever sent anywhere.