How to Compare Two Texts Online and Spot Every Difference

Text comparison — finding exactly what changed between two versions of a document — is a daily task across many professions. A text diff tool handles this instantly, highlighting every addition and deletion without manual reading.

What a text diff tool shows you

• Additions (green) — text in the second version that was not in the first
• Deletions (red, strikethrough) — text removed from the first version
• Unchanged text — content identical in both versions

How the algorithm works

The standard approach uses the Longest Common Subsequence (LCS) — the longest sequence of words appearing in both texts in the same order. Everything in text A not in the LCS is a deletion; everything in text B not in the LCS is an addition. This is the same algorithm used by git diff and most code review tools.

This tool performs word-level diffing which produces readable output for natural language. Character-level diffing is better for code where a single character change carries meaning.

Common use cases

Writing and editing — See what a client, editor, or co-author changed between two drafts instantly.

Contract comparison — Identify added, removed, or modified clauses in seconds rather than hours.

SEO content auditing — Confirm a keyword, paragraph, or CTA is present in an updated page version.

Translation verification — Check that translated text has the same structural elements as the source.

Plagiarism check — Paste similar articles to see overlap and differences at a word level.

Limitations

For code comparison use a character-level diff tool or your IDE's built-in diff viewer. Very large texts may be slow because the LCS algorithm is O(n×m) in complexity.

Frequently asked questions