Markdown Preflight

Markdown publishing compatibility checker

Paste a draft or open a local .md file. Markdown Preflight prepares one handoff per destination and lists every change, every manual step, and the dated test behind each rule.

Your Markdown

Your draft stays in this browser. Nothing is uploaded.

0 characters, 0.0 KB
Source context (optional)

Relative links and local files stay unresolved until you confirm where they point. Each unresolved target gets its own manual step rather than a guess.

What each destination needs

There is no single correct export, because the five editors disagree. These are the tested handoffs, each one chosen because it beat the alternatives in a live paste on 2026-08-24.

What it checks for

Front matter, heading depth and anchors, nested and task lists, tables of any width, fenced and long-line code, footnotes, inline and block math, Mermaid diagrams, raw HTML, Obsidian wiki links and callouts, local and remote images, relative links, unsafe link schemes, and Unicode including CJK, right-to-left text, and emoji. Each one gets an outcome per destination, and anything that needs your hands gets a step with the content preserved.

Where the rules come from

Every rule traces to a dated test in a real editor with a screenshot saved. Where a construct was never tested on a platform, the result is reported as unknown rather than guessed. See how the tests are run or the five-platform comparison.

What this tool does not promise