[BUG] Mismatch of YAML frontmatter skill format

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The spec says "YAML frontmatter" but the web
implementation is really "a strict subset of YAML that only accepts name and description as
double-quoted inline strings." That's not YAML, that's a custom format wearing a YAML costume. At
minimum they should either use a real YAML parser (js-yaml handles all of this) or document the
restrictions explicitly rather than showing a generic "malformed" error.

What Should Happen?

One format that works fine with Claude Code and Claude.ai

Error Messages/Logs

Steps to Reproduce

Create a perfectly valid skill for Claude Code that is accepted and functions. Upload same skill to the web and receive error:

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.2.234

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_