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

Goes well past the annotations: per-call charge of $0.01 (x402 USDC or card key), first 25 free, failed calls free, and 'repeats are not free', which explains why idempotentHint is false despite being read-only. It also discloses the key execution constraint, 'Server HTML only', i.e. no JS rendering — exactly the kind of trap an agent would otherwise fall into.

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?

Front-loaded: the capability enumeration comes first, usage second, and commercial/payment terms last where they can be skimmed. The single pricing sentence is dense but carries genuinely decision-relevant facts; a slightly tighter split would be cleaner.

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?

There is no output schema, and the description compensates by listing the returned sections (title/description lengths, canonical, headings, alt text, structured data, score, issues, keywords, OG/Twitter, favicon, robots.txt sitemaps). Combined with the server-HTML caveat and cost model, an agent has everything needed to call it or reject it.

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?

Only one parameter and schema coverage is 100% ('Absolute http(s) URL of the page'), so the schema does the work. The description adds a worked example (url=https://www.wikipedia.org/) that shows expected granularity, which is modest but real added value.

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?

Opens with a specific verb+resource ('on-page SEO analysis of a URL') and then enumerates exactly what is computed: audit fields, keyword/two-word density, social preview, favicon, robots.txt/sitemaps. That enumeration is what distinguishes it from siblings like seo_audit, url_meta, url_favicon, robots and text_keyword_density — it is explicitly the bundle.

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?

'Use before publishing, for an SEO report or to compare a competitor's page' gives concrete usage contexts, and 'Cheaper than the tools one by one' signals it supersedes the singles. It never names the actual alternative tools (seo_audit, url_meta, pack_website_audit), so the agent must infer the routing, and no when-not-to-use case is given.

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