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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.

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Claude Code v2.1.221

The Agent SDK validates skills entries before turning them into permission rules

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Useful3 Signal0
Agents

The SDK now rejects malformed skill names with a clear reason instead of creating a rule that never matches.

skills
What

Each name in the SDK skills option is now checked before it becomes a Skill(name) allowed-tool rule, so a name that could never match is reported instead of silently producing a dead rule.

Details
  • Rejects empty names, unpaired surrogates, leading or trailing whitespace, parentheses, commas, control characters, wildcard suffixes, a leading slash, consecutive backslashes and a trailing unpaired backslash.
  • Each rejection carries a specific explanation of why the resulting rule could not match.
  • Applies to everyone using the SDK skills option; no gate.
Evidence

Invalid skill name '*': use skills: 'all' to enable every skill.

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 v2.1.221 →