Text Diff Checker

A text diff checker that compares two versions line by line using the longest-common-subsequence algorithm, marking removed lines with a minus and added lines with a plus so you see exactly what changed — including small insertions in the middle of long documents.

This tool compares two texts line by line and shows exactly what changed: paste the original in the first box and the new version in the second, and you get a report with unchanged lines plain, removed lines marked with a minus, and added lines marked with a plus — the same convention developers have trusted in code diffs for decades. That answers "what exactly did they change?" — the question behind every contract revision, edited article, updated policy and reworked email, where reading two versions side by side and spotting differences by eye is slow and unreliable.

Under the hood it computes a longest-common-subsequence alignment, the classic diff algorithm, so it finds the minimal set of changes rather than declaring everything after the first difference "changed". Insert a paragraph in the middle of a document and the diff shows exactly that one insertion, with everything after it still recognised as unchanged.

Typical uses: checking a supplier's "minor updates" to a contract before re-signing, verifying which clauses a landlord edited in a rent agreement, reviewing a colleague's changes to marketing copy, comparing two exports to find the records that differ, or confirming that a template you re-generated matches the old one. Since comparison runs entirely in your browser, it's safe for confidential documents — nothing is transmitted or stored. For prose with heavy rewording inside lines, split it into shorter lines or sentences first for a more granular result.