Diff Checker Pro

Compare two texts line-by-line or word-by-word, with side-by-side and unified views — fast, private, and fully offline.

A premium, zero-dependency text diff workbench. Paste two versions of a document, get an instant line- or word-level comparison powered by a hand-written LCS diff algorithm, and read a live summary of what changed — all in your browser, with nothing ever leaving your machine.

Overview

Diff Checker Pro is part of the Web Utility Suite. It runs entirely in the browser with no build step, no frameworks, and no network calls — open index.html from disk and it works. Paste the original text into Text A and the modified text into Text B; the diff recomputes live as you type. Choose Line or Word granularity and Unified or Side-by-side view independently, and read the added/removed/changed/unchanged counts in the summary bar.

Features

• Line and word-level diffing — compare whole lines or individual words/whitespace tokens.
• Unified and side-by-side views — a classic +/- inline diff, or two aligned columns with additions and deletions color-coded and blank fillers keeping rows in sync.
• Self-written LCS diff algorithm — a real longest-common-subsequence dynamic-programming implementation (no external diff library), with a size guard that shows a friendly message instead of freezing the tab on pathological input.
• Live summary bar — counts of added, removed, changed (paired add+delete hunks), and unchanged lines/words, plus a status badge ("Identical" / "N changes").
• Swap — instantly swap Text A and Text B and re-diff.
• Copy and Download the diff as a plain-text +/-/ prefixed file.
• Load sample — a realistic before/after pair to explore the tool.
• Auto-persist — your last inputs and view settings are saved to localStorage and restored on return.
• Dark & light themes, fully responsive down to 360px, accessible, and keyboard-driven.

Installation

No dependencies, no build step.

git clone https://github.com/kasapdev/diff-checker-pro.git
cd diff-checker-pro

Then simply open index.html in any modern browser (double-click it, or file:// it). That's it.

Usage

1. Paste the original text into Text A and the modified text into Text B — or click Sample to load an example.
2. Choose Line or Word granularity, and Unified or Side-by-side view — the diff updates instantly.
3. Use Swap to flip A and B, or Clear to reset both panes.
4. Read the summary bar for added/removed/changed/unchanged counts and the status badge.
5. Copy the diff or Download it as a .diff text file.

Keyboard Shortcuts

Action	Shortcut
Re-diff now	Ctrl/⌘ + Enter
Download diff	Ctrl/⌘ + S
Swap Text A / Text B	Ctrl/⌘ + Shift + X
Show shortcuts help	?
Close dialog	Esc

Screenshots

Screenshots coming soon.

Roadmap

• Character-level diff highlighting within changed words
• Ignore-whitespace and ignore-case toggles
• File upload for Text A / Text B
• Syntax-aware diffing for common code/config formats
• Shareable diff links via a compressed URL fragment

License

MIT Licensed. Part of the Web Utility Suite.