If Claude doesn’t seem to follow a Skill you created, test its behavior with clear matching prompts, near misses, and unrelated requests. Skills are selected dynamically according to relevance; a response that follows a distinctive instruction from your Skill is useful evidence, but it does not prove how Claude made its selection.
Why Claude may not use a Skill on every related request
A Claude Skill is a folder containing a SKILL.md file. Its YAML frontmatter must include name and description; the description should say what the Skill does and when Claude should use it. Anthropic lists a maximum description length of 1,024 characters in its Agent Skills overview. That is a format limit, not a recommended target length or a trigger threshold.
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Anthropic’s Claude Help Center explains: “When you ask Claude to complete a task, it reviews available skills, loads relevant ones, and applies their instructions.” See “What are skills?” This describes relevance-based selection, not a guarantee that every prompt touching the same broad subject will invoke a Skill.
Check that the Skill is available and valid
- Make sure the Skill is installed or available in the Claude product surface where you are testing, and that it is enabled.
- Check that
SKILL.mdhas valid YAML frontmatter and includes the requirednameanddescriptionfields. The Agent Skills overview describes the format. - Confirm the current plan and settings for that surface. Anthropic’s Help Center article says Skills are available on Free, Pro, Max, Team, and Enterprise plans and that code execution must be enabled. Product availability and settings can change, so check the interface you are using.
Test matching prompts, near misses, and unrelated tasks
The following is a practical test method based on Anthropic’s documented relevance-based behavior—not an official Anthropic testing protocol. Keep the context consistent, and look for a distinctive instruction in your Skill, such as a required sequence, output format, or question Claude should ask.
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- Write at least three clear positive prompts. Make each request plainly fit the Skill’s stated task and conditions. Use the terms and circumstances named in its description.
- Add boundary prompts. Use similar vocabulary but change a key condition so the request falls outside the Skill’s stated use case. These show whether the description distinguishes a true match from a near miss.
- Add unrelated negative controls. Ask for tasks that should not involve the Skill. Note whether its distinctive steps or format appear anyway.
- Run each prompt more than once. Use a fresh conversation for each run, or otherwise keep context consistent. Record the exact prompt, Claude surface, whether the Skill was enabled, and whether the answer followed a distinctive instruction.
- Change one thing at a time. Start with the description, then repeat the same prompt set. A controlled comparison makes it easier to see whether a revision changed observable behavior.
Improve the description before expanding the instructions
Because the description is discovery information, make it explicit about the task, the conditions for using the Skill, and the phrases or requests that signal that task. For example, a description that says only “Helps with documents” gives less guidance than one that names the document task and the circumstances in which it applies. This is a reasoned authoring recommendation, not a guaranteed fix: Anthropic does not publish a deterministic trigger threshold.
If a Skill’s distinctive directions are missing from matching responses, clarify the description and rerun the same tests before adding more body text to SKILL.md. Keep the body focused on the instructions Claude should apply after the Skill is relevant.
What a test can—and cannot—tell you
If Claude repeatedly follows a distinctive instruction on clear positive prompts, that is useful observable evidence that the Skill’s behavior is being applied. If it does not, one failed response alone does not establish that the Skill was unavailable or never selected. Likewise, seeing the behavior does not reveal Claude’s internal selection process.
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Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to include when asking for help
If the behavior remains unclear, provide the Claude surface you used, whether the Skill was enabled, its name and description, and the exact prompts and observed responses. Include positive, boundary, and unrelated examples so others can understand what you expected and what happened. Do not assume a universal hidden-selection audit mechanism is available.
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