Free Text Diff Checker

This tool uses an LCS (Longest Common Subsequence) algorithm — the same foundational approach used by git diff. It finds the longest sequence of tokens that appear in both texts in the same order, then marks everything else as added or removed. This guarantees the minimal edit distance between the two texts.

Line mode splits both texts by newline (\n) and compares line by line — ideal for code, documents, and multi-paragraph text. Word mode splits by whitespace and compares individual words — best for prose editing. Character mode compares every single character — useful for precise typo detection and short strings.

Similarity is calculated as (unchanged tokens × 2) / (total tokens in both texts), expressed as a percentage. 100% means the texts are identical. 0% means they share no common tokens. This metric is equivalent to a simplified Dice coefficient.

Ignore Whitespace trims leading and trailing spaces from each line before comparison. This means a line with extra indentation or trailing spaces is treated as equal to the same line without. It does not ignore spaces within a line.

Ignore Case converts both texts to lowercase before comparison. 'Hello' and 'hello' are treated as identical. The original capitalisation is still shown in the output for readability.

This tool compares two specific texts you provide — it does not search the web or any database. For academic plagiarism detection, use a dedicated service. However, this tool is very useful for comparing a suspected plagiarised passage against an original source you have access to.

No. All diff computation happens locally in your browser using JavaScript. Neither Text A nor Text B is ever sent to our servers, stored in any database, or shared with any third party.

There is no hard limit. For texts over 600 lines or 600 tokens per mode, the tool automatically switches to a faster prefix/suffix trimming algorithm that is slightly less precise but handles large inputs without any slowdown.