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

With no annotations, the description carries the full burden and does so well: it discloses the 7 s timeout cap, the specific failure classes (403/404/5xx, CDN/WAF challenge, timeout), the 422 response with score null and a reason, the charged:false guarantee that no payment is taken, and the $0.012 x402 price. These are exactly the billing and failure semantics an agent needs before invoking a paid tool.

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?

Three dense sentences plus a price clause, front-loaded with what the tool does and followed by failure and cost behavior. Every sentence adds information and nothing is padding.

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 two-parameter tool with no output schema and no annotations, the description covers purpose, failure modes, and payment well, and it does describe the returned score including the null-on-error case. The remaining gap is parameter meaning, which is left entirely to the bare schema.

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?

Schema description coverage is 0%, so the description must compensate, but it never explains the two parameters. The 'keywords' parameter is only glancingly alluded to via the list of checks and it is unclear whether it supplies target keywords or merely reports extracted ones, and the url constraints (maxLength 2000) go unmentioned.

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: 'Fetches a URL and returns an on-page SEO score,' and enumerates the checks (title, meta, headings, alt text, keywords), which separates it from siblings like url_to_markdown, html_clean, and keyword_extract. It does not explicitly name an alternative, so it falls just short of a 5.

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?

Usage is only implied: run it against a URL to get an SEO score. There is no statement of when to prefer this over keyword_extract or url_to_markdown, and no when-not guidance beyond the failure cases, which describe error handling rather than tool selection.

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