42 Skills Point at example.com. Which Ones Mean It?

A placeholder domain is a good documentation habit and a bad execution instruction. Skills blur the two more often than you would expect.

Scanning the corpus for the reserved documentation domain:

The average score of the 42 is 8.70 — slightly above the corpus average. These are not broken skills. They are skills using a standard documentation convention in a context where the convention has a second meaning.

The two kinds of placeholder

Illustrative. A URL appears in an example response or an explanation:

> The API returns a JSON object: {"url": "https://example.com/page"}

This is correct usage. example.com exists precisely so examples can be unambiguous. No agent will call it.

Instructional. A URL appears in a workflow step or a code block the agent is meant to execute:

curl https://api.example.com/v1/generate \
  -H "Authorization: Bearer $API_KEY"

This is where it gets ambiguous. Is the agent supposed to replace the host, or call it? The skill may explain elsewhere, but the code block is what the agent copies.

What the safer version looks like

Make the host a variable with a required value, and fail loudly if it is unset:

: "${API_BASE_URL:?Set API_BASE_URL to the provider base URL}"
curl "$API_BASE_URL/v1/generate" -H "Authorization: Bearer ${API_KEY:?}"

Two changes: the example host is gone from executable code, and a missing configuration stops the skill instead of sending a request to a reserved domain.

For prose examples, keep example.com — it is the right tool. The problem is only when illustrated and executable text share the same literal.

The placeholder-token count

Eleven skills contain tokens like <YOUR_KEY> or YOUR_API_KEY. Some explain how to replace them; some do not. An agent that follows a code block literally will send <YOUR_KEY> as the header value and receive a 401, then have to infer that angle brackets are not part of the key.

A one-line rule prevents this:

> Never execute a code block containing <...>; replace the placeholder with a value from the environment first.

The general principle

Skills are executed text, not documentation. A convention that is unambiguous to a human reader — "this domain is fake" — is not necessarily unambiguous to an agent that pattern-matches a URL out of a code block.

The fix is cheap: separate illustration from instruction, and make every executable endpoint come from a variable that must be set.