Showdown
Bidirectional Markdown-to-HTML converter (and HTML-to-Markdown) for JavaScript, working in both browser and Node.js. Supports GitHub Flavored Markdown extensions (tables, strikethrough, fenced code blocks) via options. Extensible with custom converters. Well-established alternative to marked.js with bidirectional conversion capability.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
MIT licensed. HTML output may contain XSS if Markdown contains raw HTML tags — always sanitize with DOMPurify or sanitize-html before browser rendering.
⚡ Reliability
Best When
You need a battle-tested Markdown converter that works in both browser and Node.js with bidirectional HTML-to-Markdown capability.
Avoid When
You only need server-side Markdown processing at high volume — marked.js or remark are faster and more actively maintained.
Use Cases
- • Convert Markdown content to HTML for agent content generation pipelines in browser or Node.js
- • Parse Markdown documentation and convert to HTML for agent knowledge base ingestion
- • Enable Markdown input in web applications that need browser-side Markdown rendering
- • Convert HTML back to Markdown for agent content normalization pipelines
- • Render agent-generated Markdown responses as HTML in chat interfaces or documentation tools
Not For
- • Performance-critical bulk Markdown processing — marked.js is faster for high-volume server-side processing
- • GitHub-flavored Markdown with all GitHub extensions — use marked-gfm or remark for comprehensive GFM support
- • MDX (Markdown with JSX) — use the @mdx-js ecosystem for React component embedding in Markdown
Interface
Authentication
Local library — no authentication required. MIT licensed.
Pricing
MIT licensed. Zero cost.
Agent Metadata
Known Gotchas
- ⚠ Must sanitize HTML output before rendering in browser to prevent XSS from Markdown inputs with embedded HTML — Showdown allows raw HTML by default
- ⚠ Create converter once and reuse: const converter = new showdown.Converter({ ghCodeBlocks: true }) — don't create new converter on each conversion
- ⚠ GFM extensions must be explicitly enabled: new showdown.Converter({ tables: true, strikethrough: true, tasklists: true }) — not enabled by default
- ⚠ HTML-to-Markdown (makeHtml → makeMd) bidirectional conversion is lossy — complex HTML structures may not round-trip cleanly
- ⚠ Showdown's latest release cadence has slowed — marked.js or remark may have better recent GFM spec compliance
- ⚠ Link handling: [links](url) work but Markdown input containing user-provided links requires URL sanitization to prevent javascript: URLs in output
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Showdown.
Scores are editorial opinions as of 2026-03-06.