Text Diff Checker
Paste two texts to instantly see what changed. Line-by-line diff with colour-coded additions and deletions, plus word-level comparison.
How to use Text Diff Checker
The Text Diff tool compares two blocks of text side by side and highlights every addition, deletion and modification using colour-coded inline markup. Based on the Myers diff algorithm (the same engine used by Git), it shows line-level changes with optional character-level highlighting, making it invaluable for comparing document revisions, contract edits, configuration files and code snippets outside of a full version-control system.
- Paste the original (left/before) text into the first input panel.
- Paste the revised (right/after) text into the second input panel.
- The diff is computed and colour-coded automatically: green for additions, red for deletions, yellow for modifications.
- Toggle "Word-level diff" to highlight individual changed words rather than entire lines.
- Toggle "Ignore whitespace" to suppress diffs caused purely by spacing or indentation changes.
- Use "Side by side" or "Unified" view depending on your preference.
Your data never leaves your device — 100% private processing.
How the Myers diff algorithm works
The Myers algorithm (Eugene W. Myers, 1986) finds the shortest edit script (SES) — the minimum number of insertions and deletions needed to transform one sequence into another. It solves the longest common subsequence (LCS) problem by working in O(ND) time, where N is the sum of input lengths and D is the edit distance. Git uses a variant of Myers as its default diff engine. The algorithm produces results that feel "natural" to humans by preferring to keep large contiguous unchanged blocks together rather than interleaving them.
Practical uses for text diff in non-developer workflows
Text diff tools are not just for developers. Legal teams use them to compare successive contract drafts and ensure no clauses were silently removed or changed. Academic editors use them to track revisions between manuscript versions. Content teams use them to audit what changed when a CMS article was updated after publication. Translators use them to identify which source paragraphs changed between versions, so only those segments need re-translating. Quality-assurance testers compare expected vs actual API responses without writing code.
| Role | What to compare | Key diff setting |
|---|---|---|
| Legal / contracts | Successive draft revisions | Character-level, ignore whitespace |
| Academic editor | Manuscript v1 vs v2 | Line-level with context |
| Content marketer | Published vs updated article | Word-level inline diff |
| Translator | Source text versions | Paragraph-level (sentence boundary) |
| Developer | Config files / API responses | Line diff with unified output |
| QA tester | Expected vs actual output | Exact character diff |
Glossary
- Edit distance
- The minimum number of single-character (or single-line) edits required to transform one string into another.
- Diff
- A representation of the differences between two files or text blocks, showing additions and deletions.
- Hunk
- A contiguous block of changed lines in a unified diff output, preceded by a @@ header.
- LCS
- Longest Common Subsequence — the longest sequence of lines (or characters) that appears in both texts in the same order.
- Unified diff
- A diff format showing context lines plus changes in a single output column, used by Git patches and code reviews.
Related reading
Frequently Asked Questions
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Why use Text Diff Checker?
- Instant results with no signup or account creation
- Works offline once the page is loaded
- Supports Unicode and multilingual text
- Copy results to clipboard with a single click
Common use cases
- Count words in an essay before submission
- Sort a list of items alphabetically
- Remove duplicate lines from CSV exports
- Change the case of text copied from PDFs
- Find and replace text across large documents
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