Anthropic Engineer Debates Use of Markdown vs. HTML in AI Agent Output

Markdown has emerged as the lingua franca of AI, especially with the proliferation of AI agents. But an Anthropic engineer argues that HTML is a better choice for output. And despite my love of Markdown, I have to say, he makes a compelling case.

“Markdown has become the dominant file format used by agents to communicate with us,” Anthropic’s Thariq Shihipar writes. “It’s simple, portable, has some rich text capability and is easy for you to edit. Claude has even gotten surprisingly good at using ASCII to make diagrams inside of markdown files.”

So what’s the problem? As hinted in that last sentence, Markdown is limited when it comes to output: This is just plain text with some formatting syntax in the form of special characters, and though it’s human-readable, it can’t be made to be as pretty and visual as HTML.

“I want richer visualizations, color, and diagrams and I want to be able to share them easily,” he adds. “I’ve started preferring HTML as an output format instead of Markdown and increasingly see this being used by others on the Claude Code team, this is why.”

He’s onto something here. If you know your Markdown history–I write about this in an as yet unfinished chapter in what might become a book about Markdown for writers–you know that when John Gruber created it, Markdown was two things: It’s a plain text formatting syntax, and a software tool that converts that plain text formatting to HTML, the language of the web. That is, Markdown was never meant to be the output. The output was always going to be HTML.

Shihipar explains, correctly, that HTML can convey much richer information than Markdown and that it can be used to create beautiful visuals with images, code snippets, interactive elements with JavaScript, designs with CSS, and much more. “There is almost no set of information that Claude can read that you cannot fairly efficiently represent with HTML,” he writes. “This makes it a highly efficient way for the model to communicate in-depth information to you and for you to review.”

I use Markdown for writing because it’s simple and fast and infinitely compatible, but it’s worth pointing out that the app I use to write, Typora, is visual in nature and provides a formatted representation of what I write using embedded hyperlinks, headline styles, bold and italic text, and the like. But many Markdown editors provide both source code and output displays, often side-by-side. The output display is HTML.

Shihipar’s post goes into more detail on this topic, but I didn’t have to get too far into it before I realized how right he is. If you think about HTML, there’s a code view with a tags-based syntax that is human readable but not pretty, and then a formatted HTML display. Markdown works the same way, it’s just a lot simpler than HTML. But if you care about this stuff, his post is absolutely worth reading. I’m curious to see what if anything comes out of this.