Free Online Text Diff & Comparison Tool

Frequently asked questions

What is a text diff tool?

A text diff tool compares two versions of a text and shows exactly what changed — which lines were added, removed, or stayed the same. diffDash highlights changes line by line and character by character.

How do I use diffDash?

Paste your original text into the left box and your updated text into the right box. The diff appears instantly — no button to press. Green rows were added, red rows were removed. Use the filter badges to focus on just additions, just deletions, or unchanged lines. Hit ↓ Download .patch to save the result.

What do the colors and symbols mean?

Green rows marked with + are lines that exist in the modified version but not the original — they were added. Red rows marked with − are lines that existed in the original but are gone — they were deleted. Dimmed rows are unchanged. Within changed lines, the exact characters that differ are highlighted more brightly so you can see the precise edit at a glance.

Can I use this to compare code?

Yes. diffDash works on any plain text including source code, configuration files, JSON, Markdown, and prose. Paste both versions and the diff output shows insertions in green and deletions in red.

What does the .patch file contain?

The downloaded patch uses the unified diff format: lines starting with + were added, lines with − were removed, and lines with a space are unchanged context. This format is understood by Git, patch utilities, and most code editors.

How does character-level highlighting work?

For lines that changed, diffDash runs a second diff at the character level using the LCS (Longest Common Subsequence) algorithm — the same technique used by Git. This pinpoints exactly which characters were added or removed within a line.

Is there a limit on how much text I can compare?

There is no hard limit. diffDash runs the diff algorithm entirely in your browser, so performance depends on your device. Texts up to tens of thousands of lines work smoothly on any modern machine.

Is my data private?

Yes. The comparison runs entirely in your browser using JavaScript. Your text is never sent to any server — making this a fully private online diff checker.