About Markdown Preflight

Markdown Preflight answers one question: what will this specific publishing editor do to this specific Markdown construct. It answers it from observation, not from documentation. Every one of the 93 rules behind the tool comes from pasting a versioned fixture into a real editor, on a stated date, with a screenshot saved.

Who runs this

Markdown Preflight is built and maintained by one person. Every test record on this site was produced by hand, in the real editor, by that person. Nothing here is generated, crowdsourced, or scraped from platform documentation, which is also why the corpus is 93 rules and not ten thousand: a rule exists only once someone has watched the editor do the thing.

What this site will and will not say

• A claim names the surface it was tested in and the date it was tested on. It describes that surface on that date, and nothing wider.
• A construct that was never tested on a destination is reported as unknown. It is not inferred from a sibling platform, and it is not filled in from a help-center article.
• Rendering is not the same across platform versions, themes, plugins, or email clients, and no result here should be read as saying it is.
• A record is never edited to match later behavior. When an editor changes, a new dated record is added and the old one is kept, so a claim you relied on last month is still there to check.

How current this is

The newest evidence on the site is dated 2026-08-24. A platform claim older than 90 days keeps its date and gains a recheck marker rather than quietly disappearing, because the observation is still true about the day it was made. A price or commission claim is different: a stale one is likely wrong now, so it is withheld instead of aged. The full protocol, including what these tests cannot tell you, is on the methodology page.

Report a rule that looks wrong

Editors change, and a rule that was right in 2026-08 can be wrong today. If one does not match what you see, say so at @SukeJ56505 on X. The useful details are the destination, the construct, what you saw instead, and the date you saw it. A confirmed report becomes a new dated record, not an edit to the old one.

How this is paid for

There are no ads and no affiliate links on the site today. If a paid link ever appears it will be labeled as one, it will sit next to the problem it actually solves, and it will never change which destination the tool recommends or how a warning is worded. Commission does not get a vote in the rules; the rules come from the records.

What it does with your draft

Nothing leaves your browser. There is no account, no upload, no AI, and no network request that carries your text, your titles, your links, or your media paths. That is enforced by tests rather than promised in a policy, and the list of what is excluded is on the privacy page.

The corpus

• All 93 rules, one page and one permanent address per rule.
• rules.json, the same corpus as one machine-readable file.
• The five-destination matrix, construct by construct.
• The dated records themselves: WordPress, Substack, Beehiiv, X, LinkedIn.