Source Intelligence

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.

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Claude Code v2.1.209

Artifact Runtime Capabilities (MCP)

Feature flag
tengu_cloth_snorkel On for this account, and not off by default

The flag server returned on for the one account this site reads, and nothing in this release compiles it off by default. The compiled default is shown below, and says which it is when we cannot read one: a fifth of gates compile in a string or a number rather than on or off, and most published releases have no gate table behind them at all. No client can see what the server returns for your account.

This account: on · anonymous baseline: on · compiled default in v2.1.209: on

These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.

Read once, for one account on one subscription tier, against v2.1.209. It isn't a statement about your account. What a flag value here can and cannot tell you

What

Published Artifact pages can now declare runtime capabilities — starting with mcp, which lets the page call the user's connected claude.ai data sources at runtime rather than embedding static data from the conversation.

Usage
Artifact tool: { capabilities: { mcp: { servers: [...] } } }
Details
  • Artifacts accept a new capabilities input that declares which runtime abilities the published page requires.
  • The first supported capability is mcp, enabling the page to call the user's claude.ai connectors (Slack, Google Drive, etc.) via window.claude.mcp at open time.
  • Omitting capabilities on a republish carries the stored declaration forward; passing {} explicitly clears all capabilities.
  • A new skill, artifact-capabilities, must be loaded before declaring any capability or writing window.claude.* runtime code — it carries the current contract's typed call definitions and per-capability guidance.
  • Type definitions (.d.ts files) for the runtime contract are extracted to a local cache directory and are authoritative over any memorized API shape.
  • Connector tools appear in the tool list as mcp__<connector>__<toolName>; the server value in the capabilities declaration is the <connector> segment.
  • Only claude.ai connectors are valid — locally-configured MCP servers cannot be declared as Artifact capabilities.
  • The dataviz/artifact skill prompt gains a new "## Live data via connected sources" section when this feature is enabled, explaining the workflow.
  • The Artifact tool description itself now mentions the capabilities input and the requirement to load the artifact-capabilities skill.
Status

[Gradual Rollout] — controlled by CLAUDE_CODE_ARTIFACT_MCP env var or tengu_cloth_snorkel feature flag.

Evidence

New skill registered as registerArtifactCapabilitiesSkill (search for "Runtime capabilities for published Artifacts"); capabilities schema added (search for "Runtime capabilities this page declares, as {name: config}"); gated by n4y() which checks CLAUDE_CODE_ARTIFACT_MCP ?? Qe("tengu_cloth_snorkel", !1)

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

See this entry in the whole of v2.1.209 →