highlight.js
Automatic syntax highlighting library for 190+ programming languages. Detects language automatically when not specified, applies token-based syntax highlighting, and outputs HTML with CSS class annotations. Works in browser and Node.js. Used for code blocks in documentation sites, blogs, and developer tools. Highlight.js v11 is a complete ES module rewrite with improved language detection accuracy.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Local computation — no network. Input code is not executed. HTML output is escaped to prevent XSS from highlighted content. BSD 3-Clause. Widely used and regularly maintained.
⚡ Reliability
Best When
You need lightweight, easy-to-integrate syntax highlighting for static code display with automatic language detection and no build step required.
Avoid When
You need VS Code-quality highlighting with TextMate grammar accuracy — use Shiki or Prism.js with themes. For interactive editors, use Monaco or CodeMirror.
Use Cases
- • Highlight code blocks in server-rendered HTML documentation or blog posts before sending to browser
- • Process agent-generated code examples for display in web interfaces with accurate language detection
- • Generate syntax-highlighted HTML from code strings in agent content pipelines
- • Add syntax highlighting to README renderers, wiki systems, and markdown processors
- • Highlight code in emails or static site generators where CSS-class-based output is needed
Not For
- • Real-time editor syntax highlighting — use CodeMirror or Monaco Editor for interactive code editors
- • Applications needing theme diversity — Shiki uses TextMate grammars (VS Code themes) for more accurate highlighting than highlight.js's custom grammars
- • Token-level AST access — highlight.js outputs HTML classes, not parse trees; use language-specific parsers for AST
Interface
Authentication
Local library — no authentication required. BSD 3-Clause licensed.
Pricing
BSD 3-Clause licensed. Zero cost for any use.
Agent Metadata
Known Gotchas
- ⚠ Auto-detection (hljs.highlightAuto) is heuristic-based and can misidentify languages — for agent pipelines, always specify the language explicitly with hljs.highlight(code, {language: 'python'})
- ⚠ highlight.js v11 dropped CommonJS support — import syntax changed from require('highlight.js') to ES module import; use 'highlight.js/lib/core' for Node.js with manual language registration
- ⚠ Loading all 190+ languages significantly increases bundle size — import only needed languages: hljs.registerLanguage('python', require('highlight.js/lib/languages/python'))
- ⚠ HTML output contains class names like 'hljs-keyword' — requires pairing with a highlight.js CSS theme file to actually display colors; HTML alone looks like unstyled spans
- ⚠ Code containing HTML special characters (<, >, &) is automatically escaped in output — don't double-escape when inserting into HTML templates
- ⚠ Server-side rendering in Node.js requires importing the full or core bundle — browser CDN builds are different from npm builds
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for highlight.js.
Scores are editorial opinions as of 2026-03-06.