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

Annotations already cover the safety profile (readOnlyHint, destructiveHint false, openWorldHint), and the description adds genuinely new behavior: the 1-credit cost and the explicit scope boundary that link crawling is excluded. It does not disclose authentication expectations around api_key or what happens when credits run out, which matters for a paid endpoint.

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?

One tight sentence plus a short scope disclaimer; the cost and the check inventory are front-loaded, and no wording 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?

The enumeration of inspected items effectively communicates the shape of the result even without an output schema, and credit cost is disclosed. However, with no output schema and zero parameter documentation, the undefined api_key/auth handling is a real hole for a tool an agent must call correctly on the first try.

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 carries the full burden. 'url' is self-evident, but 'api_key' with an empty-string default is never mentioned — an agent gets no signal on whether it must supply a key or whether the default implies optional/pre-authenticated calls.

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+resource ('on-page SEO check') and enumerates exactly what is inspected: title, meta description, headings, alt coverage, canonical, Open Graph, robots.txt, sitemap.xml. The closing 'Skips link crawling' separates it from check_broken_links and scan_website without needing their schemas.

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?

The 'Fast on-page SEO check (1 credit)' framing plus 'Skips link crawling' tells an agent this is the cheap single-page audit rather than a crawl, which implicitly routes link checking elsewhere. It stops short of naming the sibling to use for crawling or full-site scans, so the alternative is inferred rather than stated.

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