Free SKILL.md validator
Paste a skill's SKILL.md below and this page checks it against the published rules for Claude Code and claude.ai skills. The most common silent failure it catches: Claude Code ignores a frontmatter field it doesn't recognize without reporting an error, so a typo like allowed_tools or disable-model-invokation just does nothing.
Everything runs in your browser. Nothing you paste is sent anywhere.
Results
What the checks are based on
- Name: up to 64 characters, lowercase letters, numbers and hyphens only, no XML tags, and it can't contain the reserved words "anthropic" or "claude" (Anthropic's skill authoring best practices). In Claude Code the name is optional and defaults to the folder name.
- Description: non-empty, up to 1,024 characters, no XML tags, written in third person, and it should say both what the skill does and when to use it. In Claude Code the description plus
when_to_useis cut off at 1,536 characters in the skill listing, so put the key use case first. - Fields: Claude Code accepts name, description, when_to_use, argument-hint, arguments, disable-model-invocation, user-invocable, allowed-tools, disallowed-tools, model, effort, context, agent, background, hooks, paths, shell, metadata, license and compatibility. claude.ai uploads and the Skills API accept only name, description, license, compatibility, metadata and allowed-tools, and fail with an "Unexpected key(s)" error on anything else.
- Body: keep it under 500 lines and move long reference material into separate files in the skill folder.
Sources: Claude Code skills docs and Agent Skills best practices. The trigger-word check is a simple word-overlap hint, not how Claude actually decides; the real test is asking for the task in a fresh session.
Starting from scratch? Use the SKILL.md builder, and read how to write a description that triggers. Want a deeper pass on just the description and sample asks? Try the skill description tester. Skill still not firing? Work through the 10-point skill-not-triggering checklist.
Made by Solo Stack Kits. If you'd rather start from skills that already pass, the free 3-skill sample has ready-made skills for proposals and client updates, and the Solo Consultant Kit adds the full set.