Pasting an AI Response's Markdown Safely: Why Raw HTML Never Runs Here

Markdown pulled from an AI response, a forum post, or anywhere else you don't fully control can technically contain a literal `<script>` tag or an HTML event-handler attribute sitting right in the text. Markdown to HTML is built so that content can never execute, and it's worth explaining exactly why, not just asserting it.

The decision underneath this: escape, not filter

Some Markdown renderers handle unsafe content by parsing it into real HTML and then running that HTML through a filter afterward, stripping out anything dangerous - a "clean up the mess after making it" approach. This tool does something structurally different: it never recognizes an angle-bracket sequence in the Markdown source as an HTML tag in the first place. It only ever matches a fixed, closed set of actual Markdown constructs - headings, bold, links, and so on. Everything else, script tags included, falls through to the parser's plain-text path.

Why that's a stronger guarantee than a filter

A filter can have a bug - a clever payload it doesn't recognize, an edge case its allow-list missed. There's a long history of exactly that happening to sanitizers across the web. This tool sidesteps the whole category of that bug: since raw angle brackets are never parsed as markup to begin with, there's no filter to have a bug in. The text is placed into the page using the same safe method browsers use for genuinely plain text, never the method that would let a string become a real, running element.

The one place real elements do get created

Two Markdown constructs deliberately do create real elements: a link (`[text](url)`) becomes a real `<a>`, and an image (``) becomes a real `<img>`. Both run their URL through a check first - only ordinary web addresses, mailto, tel, and relative links are allowed through. A `javascript:` URL typed into otherwise-valid link syntax keeps its visible text but never gets an `href` at all, so clicking it does nothing dangerous.

What this means practically, pasting an AI response

You can paste Markdown from a source you don't fully trust and know that nothing in it will execute in your browser - a stray script tag shows up as literal, visible text, exactly as typed, never as a live element doing something. That's the honest, safe outcome for previewing content you didn't write yourself.

What this doesn't do

Raw HTML blocks - a real, supported Markdown feature in the full specification, meant to let you drop actual HTML into your document - are never rendered as live markup here, on purpose. If you genuinely need to preview raw HTML alongside Markdown, that's a different tool's job; this one is for previewing Markdown safely, including Markdown you don't fully trust.

For the preview steps themselves, see the how-to guide. For why previewing matters before publishing at all, this piece covers it. Or preview Markdown now.