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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

All of v2.1.239 Home All releases olderv2.1.238 v2.1.240newer
Claude Code v2.1.239

Mermaid diagrams render by default

Use it now
Useful4 Signal2
Rendering not in their notes

Code blocks tagged mermaid now always render as diagrams, no capability probe involved.

mermaid
What

Fenced code blocks tagged mermaid are turned into rendered diagram blocks wherever Claude Code emits formatted output, such as artifacts and pull request bodies. Rendering used to depend on a runtime probe for diagram support, which could silently leave diagrams as plain code; that probe is gone and the language tag on the fence is now the only condition checked.

Details
  • The rendering option defaults to true instead of to the result of a support check, so diagrams appear unless something deliberately opts out.
  • A caller passing mermaidOn: false still disables rendering and leaves the fence as ordinary code.
  • A matching fence is emitted as a <pre class="mermaid"> block for the diagram renderer to pick up.
Evidence

<pre class="mermaid">, mermaidOn

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.239 →