Text Diff Checker

A text diff checker compares two blocks of text line by line and highlights what was added, removed, or unchanged. It uses the LCS (Longest Common Subsequence) algorithm — the same algorithm behind git diff and Unix diff — to compute the minimal set of changes between the two inputs. Use it to compare API response versions, review config changes, spot differences in copy drafts, or verify that a refactor did not change output.

Reading the output

Lines in green prefixed with + are in the new text but not the original. Lines in red prefixed with - are in the original but not the new text. Unchanged lines are shown in grey for context. This is the unified diff format familiar from code review tools like GitHub and GitLab.

When to use a text diff vs git diff

Use git diff for code tracked in a repository — it has access to full history, commit context, and syntax highlighting. Use this browser tool when you have two text blobs that are not in version control: a before/after copy paste from a CMS, two configuration files from different environments, two versions of a JSON API response, or two AI prompt drafts you want to compare.

This tool performs line-by-line diffing. For word-level or character-level diffing (useful for spotting single changed words in long paragraphs), a more specialised tool is needed. The LCS algorithm here works well for structured text (code, config, Markdown) and line-oriented prose.