Code blocks declare a language
Knowing the language of a code block lets agents apply the right tokenizer, syntax highlighter, and execution sandbox. Untagged blocks force agents to guess from the content, which is frequently wrong on short snippets.
How the check decides
The check finds every <pre><code> block on the page and inspects the class attribute on both the <code> element and its <pre> parent for a language-* or lang-* token. Passes if every block has at least one. Fails (with the count of unlabelled blocks) otherwise. Returns N/A if the page has no code blocks at all.
How to implement it
In source markdown, always declare the language after the opening fence: ```typescript, not just ```. Most syntax highlighters (Shiki, Prism, highlight.js) emit class="language-<lang>" automatically when given a fenced code block with a language.
Pass
<pre><code class="language-typescript">const x = 1;</code></pre>
Fail
<pre><code>const x = 1;</code></pre>