Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations only declare it is non-read-only, non-destructive and closed-world; the description adds the important context that no email or payment is required, that a key with 25 credits is issued, and that the key must be retained for later calls. It does not cover idempotency or whether calling twice creates multiple keys, leaving a small gap.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short sentences, front-loaded with the core action and its benefit, followed by the one post-call instruction that matters. No redundant or filler wording.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a parameterless tool with no output schema, the description supplies everything needed: what it creates, what it costs (nothing), and what to do with the returned key. There is no hidden complexity left unexplained.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes zero parameters, so there is nothing the description needs to disambiguate; baseline for a parameterless tool is 4. The description correctly avoids inventing inputs.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: 'Register a free SiteDoctor API key', plus concrete terms (25 credits, no email or payment). This is clearly distinguishable from siblings like add_credits and check_credits, which manage credits rather than create a key.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly tells the agent what to do with the result: 'Store the returned key and pass it as api_key to the scanning tools', which effectively routes usage toward scan_website/check_page_seo. It does not state whether repeated calls are safe or when not to call it, so it falls short of full when/when-not coverage.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.