MD vs OPML
A detailed comparison of Markdown and OPML Outline — file size, quality, compatibility, and which format to choose for your workflow.
Markdown
Documents & TextMarkdown is a lightweight markup language that uses plain text formatting syntax. It is widely used in software development, technical documentation, and content management systems.
About MD filesOPML Outline
Documents & TextOPML (Outline Processor Markup Language) is an XML format for structured outlines and lists. It is most widely used for exchanging RSS feed subscription lists between podcast apps and feed readers, and for hierarchical note-taking.
About OPML filesStrengths Comparison
MD Strengths
- Readable as plain text even before rendering — fits in version control beautifully.
- Dead-simple: 90% of needs covered in 10 minutes of learning.
- Converts trivially to HTML, PDF, EPUB, and DOCX via Pandoc.
- Every modern IDE, note-taking app, and developer tool renders it natively.
- Lightweight — a typical Markdown file is kilobytes, not megabytes.
OPML Strengths
- Standard RSS subscription interchange format.
- Simple XML — easy to parse and generate.
- Highly extensible via arbitrary attributes.
- Supported by every major outline and RSS tool.
Limitations
MD Limitations
- No formal authoritative spec — CommonMark, GFM, and MultiMarkdown differ on edge cases.
- Tables and complex layouts are clunky; footnotes and math require extensions.
- Links to images stay external — no embedded media unless you base64-inline.
- Styling is limited to what HTML allows — custom branding requires CSS outside Markdown.
OPML Limitations
- XML verbosity — larger than a JSON-based equivalent.
- Specification is loose — different tools disagree on edge cases.
- Primary use (RSS reading) has shrunk dramatically since Google Reader.
- No strong central stewardship.
Technical Specifications
| Specification | MD | OPML |
|---|---|---|
| MIME type | text/markdown | text/x-opml |
| Extensions | .md, .markdown, .mdown, .mkd | — |
| Standard | CommonMark, GitHub Flavored Markdown (GFM) | OPML 2.0 (2006) |
| Encoding | UTF-8 (conventional) | — |
| Companion spec | RFC 7763 (2016) | — |
| Extension | — | .opml |
| Format | — | XML with nested <outline> elements |
| Primary use | — | RSS subscription interchange |
Typical File Sizes
MD
- README 1-15 KB
- Blog post 2-30 KB
- Full technical manual 50 KB - 2 MB
OPML
- Typical RSS reader export (50 feeds) 5-30 KB
- Deep outline (Scrivener novel plan) 20-200 KB
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Frequently Asked Questions
Markdown is a lightweight text-based markup language created by John Gruber and Aaron Swartz in 2004. A .md file uses simple conventions (*italic*, **bold**, # headings, - lists) that compile to HTML. It became the default writing format for GitHub READMEs, Stack Overflow posts, Discord messages, and most developer documentation.
Markdown files are plain text — open in any text editor. For formatted preview use VS Code (built-in preview), Typora, Obsidian, or upload to GitHub/GitLab which render Markdown automatically. Every note-taking app (Notion, Bear, Joplin) handles Markdown natively.
Use KaijuConverter's Markdown-to-PDF converter, or command-line Pandoc (the gold standard — installed with one command, converts MD to PDF/HTML/DOCX/EPUB in a single line). VS Code with Markdown PDF extension also works locally.
Markdown for almost everything — it's 10× faster to write, version-control-friendly, and compiles to HTML automatically. Write raw HTML only when you need fine control over layout, embedded JavaScript, or features Markdown doesn't support (complex tables, forms). Static-site generators (Hugo, Astro, Jekyll) compile MD to HTML for you.
Markdown never had a formal spec for its first decade. CommonMark (2014) and GitHub Flavored Markdown (2017) standardized the core syntax, but edge cases (nested lists, HTML embedding, table syntax) still differ across renderers. For portability, stick to basic GFM features.
Yes — most modern doc tools are built on Markdown. MkDocs, Docusaurus, Astro Starlight, GitBook, and Read the Docs all accept Markdown input. For documentation needing rich features (tabs, callouts, versioning), MDX (Markdown + JSX components) extends MD with React-style embeds.