About the Text Diff Checker
A fast, private, browser-based tool for comparing two texts and highlighting exactly what changed.
What it is
The Text Diff Checker is a free, client-side tool that compares two blocks of text and highlights every difference — additions, deletions, and changes — at the line level and right down to individual words or characters within a changed line. Paste your original text in one pane and the updated version in the other, and the diff appears instantly.
Everything runs in your browser using JavaScript. No text is sent to a server — your content stays entirely on your device. The tool is designed for developers comparing config files, writers reviewing drafts, and anyone who needs to quickly understand what changed between two versions of any plain text.
How diffing works
The tool uses the Longest Common Subsequence (LCS) algorithm to identify the largest set of lines that appear in both texts in the same order. Lines not in the common sequence are classified as deletions (in the original only) or additions (in the changed version only). For lines that were modified rather than simply added or removed, a second LCS pass runs on the words or characters within those lines to pinpoint the exact changed segments.
Features
Line-level diff
LCS algorithm finds the minimal set of changes across all lines.
Word & char diff
Highlights the exact words or characters that changed within a modified line.
Side-by-side view
Two aligned columns so you can read original and changed versions together.
Inline view
Unified diff stream with − and + markers — the format familiar from git diff.
Ignore case & whitespace
Filter out formatting noise so only meaningful changes show up.
Change summary
At-a-glance +N / −M count of lines added and removed.
Copy unified diff
One click copies a standard unified diff patch to your clipboard.
Fully private
No server, no storage — everything runs in your browser.
Accessibility
Added and removed lines are marked with + and − symbols in addition to color coding, so the diff is readable for users who cannot distinguish red from green. Color is used as a reinforcement, not as the sole signal.