What Is a Text Diff?

A diff (short for difference) is a comparison between two versions of text that shows exactly what changed. The concept comes from the Unix diff command, which compares files line by line. Modern diff tools extend this to character-level comparison, making it easy to spot even a single changed character in a long block of text.

Diffs are used by developers to review code changes (pull requests show diffs), by editors to track document revisions, by translators to compare source and translated text, and by anyone who needs to audit changes between two versions of any content.

Types of Text Comparison

Type	Granularity	Best For
Line-by-line diff	Whole lines	Code files, scripts, config files
Word-level diff	Individual words	Documents, articles, translated text
Character-level diff	Single characters	Spotting typos, small edits in data
Semantic diff	Meaning	Comparing paraphrased or restructured text

How to Read a Diff

Standard diff output uses a colour-coded convention:

• Red / strikethrough — text removed from the original (left side).
• Green / underline — text added in the new version (right side).
• No highlight — text unchanged in both versions.

A line that appears both red and green means it was modified — the old version is shown in red, the new version in green. Some tools merge these into a single line with inline character-level highlighting.

Common Use Cases for Text Comparison

• Code review — see what a colleague changed before merging a pull request.
• Document revision tracking — compare draft 1 vs draft 2 of a report or contract.
• Translation review — ensure the translated text covers all content from the source.
• Copy editing — confirm an editor's changes before publishing.
• Data validation — compare two CSV exports to find discrepancies.
• Academic work — compare an original essay against a revised version.

Tips for Accurate Text Comparison

• Normalise whitespace first — extra spaces or different line endings can show false differences. Use our Whitespace Remover before comparing if needed.
• Match encoding — UTF-8 vs ASCII differences can appear as garbled characters in a diff.
• Use line-level diff for code and word/character-level diff for prose.
• Compare plain text — strip HTML or Markdown formatting before comparing if you want to see only content differences.

How to Compare Two Texts Online

Open the ToolsBox Text Diff Checker. Paste your original text in the left panel and the new version in the right panel. Click Compare and every difference is highlighted instantly — additions in green, deletions in red. No account, no download, and your text never leaves your browser.

Frequently Asked Questions

What is a text diff?

A text diff compares two versions of text and highlights additions (green), deletions (red), and unchanged sections. The term comes from the Unix 'diff' command. Modern diff tools work at line, word, or character level.

What does a red/green highlight mean in a diff?

Red (or strikethrough) means text was removed from the original. Green means text was added in the new version. Unchanged text is shown without highlighting. Some tools also highlight changes within a line at the character level.

Can I compare two Word documents?

Paste the text content from each document into the diff tool. For tracking changes inside Word itself, use Review > Compare Documents. For plain-text comparison in your browser, the ToolsBox Text Diff Checker is the fastest option.

Is the text I compare sent to a server?

No. The ToolsBox Text Diff Checker runs entirely in your browser using JavaScript. Your text is never uploaded to any server, making it safe for confidential documents, contracts, or proprietary code.