# Markdown Preflight > Check a Markdown draft before you paste it into a publishing editor. > > One draft, five destination-specific handoffs, with every change and every loss named and > traced to a dated live test. Static, browser-local, no account and no upload. Every claim on this site is one observation: what one named publishing editor did to one named Markdown construct, in one named surface, on one stated date. Nothing is inferred from platform documentation or marketing. A construct that was never tested on a destination is reported as unknown rather than guessed, and a claim is only as current as the test date printed beside it. Rendering is not identical across platform versions, themes, plugins, or email clients. Current corpus: 93 rules across 5 destinations. Fixture markdown-portability-test-v1. Newest evidence 2026-08-24. ## Machine-readable - [rules.json](https://markdownpreflight.com/rules.json): every rule as JSON: id, matched construct types, and one application per destination with outcome, severity, confidence, the tested surface, the test date, and the evidence record. Prefer this over scraping the 93 HTML rule pages. - [Rule index](https://markdownpreflight.com/rules/): the same corpus as one HTML table, one row per rule. ## By construct The same evidence indexed by what is in the draft rather than by destination. One page per construct, each naming what all five editors did with it. - [Tables](https://markdownpreflight.com/constructs/tables/): Do Markdown tables survive WordPress, Substack, Beehiiv, X, and LinkedIn? - [Footnotes](https://markdownpreflight.com/constructs/footnotes/): What happens to Markdown footnotes in WordPress, Substack, Beehiiv, X, and LinkedIn - [Math](https://markdownpreflight.com/constructs/math/): Does LaTeX math survive WordPress, Substack, Beehiiv, X, or LinkedIn? - [Images](https://markdownpreflight.com/constructs/images/): What happens to Markdown images in five publishing editors - [Links](https://markdownpreflight.com/constructs/links/): Absolute, relative, anchor, and mailto links across five publishing editors - [Obsidian syntax](https://markdownpreflight.com/constructs/obsidian-syntax/): Publishing an Obsidian note: wikilinks, embeds, callouts, and block refs - [Code](https://markdownpreflight.com/constructs/code-blocks/): Do fenced code blocks survive WordPress, Substack, Beehiiv, X, and LinkedIn? - [Headings](https://markdownpreflight.com/constructs/headings/): What happens to Markdown headings and heading anchors in five editors - [Lists](https://markdownpreflight.com/constructs/lists/): Do nested Markdown lists and checkboxes survive five publishing editors? - [Inline formatting](https://markdownpreflight.com/constructs/text-formatting/): Does Markdown bold, italic, and strikethrough survive five publishing editors? - [Front matter](https://markdownpreflight.com/constructs/front-matter/): What happens to YAML front matter when you paste Markdown into an editor - [Raw HTML](https://markdownpreflight.com/constructs/raw-html/): Does raw HTML inside Markdown survive five publishing editors? - [Mermaid diagrams](https://markdownpreflight.com/constructs/mermaid-diagrams/): Do Mermaid diagrams render in WordPress, Substack, Beehiiv, X, or LinkedIn? - [Quotes, dividers, and line breaks](https://markdownpreflight.com/constructs/quotes-and-breaks/): Blockquotes, horizontal rules, and hard line breaks across five editors - [All constructs](https://markdownpreflight.com/constructs/): the index of the above, with a one-line verdict each. ## Evidence records Each record reproduces what was observed on its test date and is never edited afterward. - [WordPress test record, 2026-08-24](https://markdownpreflight.com/evidence/wordpress/): the fixture pasted into WordPress.com desktop Block Editor, with screenshots. - [Substack test record, 2026-08-24](https://markdownpreflight.com/evidence/substack/): the fixture pasted into Substack web post editor, with screenshots. - [Beehiiv test record, 2026-08-24](https://markdownpreflight.com/evidence/beehiiv/): the fixture pasted into Beehiiv web Visual Editor, with screenshots. - [X test record, 2026-08-24](https://markdownpreflight.com/evidence/x/): the fixture pasted into X web post and thread composer, with screenshots. - [LinkedIn test record, 2026-08-24](https://markdownpreflight.com/evidence/linkedin/): the fixture pasted into LinkedIn desktop web Create post composer, with screenshots. ## Destination guides - [Markdown to WordPress: what a Gutenberg paste keeps and breaks](https://markdownpreflight.com/tools/markdown-to-wordpress/): handoff mode: Gutenberg paste. - [Markdown to Substack: why raw paste fails and rich paste is the handoff](https://markdownpreflight.com/tools/markdown-to-substack/): handoff mode: Rich HTML clipboard. - [Markdown to Beehiiv: clean Markdown paste beats rich HTML](https://markdownpreflight.com/tools/markdown-to-beehiiv/): handoff mode: Clean Markdown paste. - [Markdown to an X post or thread, with weighted character counts](https://markdownpreflight.com/tools/markdown-to-x-thread/): handoff mode: Plain text. - [Markdown to a LinkedIn post, counted in UTF-16 code units](https://markdownpreflight.com/tools/markdown-to-linkedin/): handoff mode: Plain text. ## Reference - [Home](https://markdownpreflight.com/): the problem, and a worked example run through the real analyzer. - [Compatibility checker](https://markdownpreflight.com/tools/markdown-publishing-compatibility-checker/): paste a draft and get all five destination results at once. - [Five-destination comparison](https://markdownpreflight.com/research/markdown-publishing-compatibility/): the construct-level matrix across all five editors. - [Methodology](https://markdownpreflight.com/methodology/markdown-compatibility-tests/): the fixture, the evidence levels, the retest policy, and what these tests cannot tell you. - [Substack vs Beehiiv for a Markdown workflow](https://markdownpreflight.com/compare/substack-vs-beehiiv-for-markdown/): the same fixture in both editors, side by side. - [About](https://markdownpreflight.com/about/): who produces the records, what a claim does and does not cover, the recheck policy, and how to report a rule that looks wrong. - [Privacy](https://markdownpreflight.com/privacy/): the draft is analyzed in the browser and is never uploaded.