diff
JavaScript text diffing library implementing the Myers diff algorithm. Produces word, character, line, sentence, JSON, and CSS diffs between two strings. Outputs unified patch format, HTML diff markup, or structured change arrays. Used in code review tools, content editing systems, test assertion output, and anywhere you need to show what changed between two versions of text. Includes patch application and reverse patch utilities.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Text processing utility — no network surface. Diff output may reveal sensitive content if applied to secrets; ensure diff results are appropriately access-controlled.
⚡ Reliability
Best When
You need to compute, display, or apply text diffs in JavaScript — for showing what changed between two versions of any text content.
Avoid When
You need binary diffing, real-time collaboration, or structured object diffing (use deep-diff or jsondiffpatch).
Use Cases
- • Show diff between agent-generated and user-edited text to highlight AI modifications
- • Display code changes in human-readable format for code review or audit logging
- • Implement undo/redo systems by storing diffs instead of full document snapshots
- • Generate unified diff patches for version-controlled document management
- • Visualize configuration changes in deployment pipelines by diffing before/after configs
Not For
- • Binary file diffing — diff handles text only; use binary diff tools for file comparison
- • Real-time collaborative editing — diff is for point-in-time comparison; use operational transform or CRDTs for real-time
- • Database schema diffs — use database-specific diff tools for schema migrations
Interface
Authentication
No authentication — text processing library.
Pricing
Fully free, BSD licensed.
Agent Metadata
Known Gotchas
- ⚠ Diff performance: Myers algorithm is O(n*m) — for very large texts (>100KB), consider chunking or streaming; large diffs can be slow
- ⚠ createPatch() vs createTwoFilesPatch(): createPatch takes oldStr/newStr; createTwoFilesPatch takes full file paths for git-like output header — choose based on display needs
- ⚠ Patch application: applyPatch() can fail if context doesn't match — fuzz tolerance configurable; returns false (not throw) if patch can't be applied
- ⚠ JSON diffing: diffJson() compares JSON objects and shows human-readable key differences — useful for config comparison, but for precise object diff use jsondiffpatch
- ⚠ Line-ending normalization: diffs on text with mixed \r\n and \n may show spurious differences — normalize line endings before diffing if cross-platform comparison
- ⚠ Word-level diff: diffWords() splits on whitespace; diffWordsWithSpace() preserves spacing in output — choose based on whether whitespace changes matter
Alternatives
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Scores are editorial opinions as of 2026-03-06.