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

Annotations already cover read-only/idempotent/open-world, and the description adds substantial behavior beyond them: the sitemap discovery order (robots.txt Sitemap: lines, then /sitemap.xml, /sitemap_index.xml, /wp-sitemap.xml), gzip support, sitemap-index expansion semantics, and the paid-tool model (x402 USDC on Base, $0.002 per successful call, PaymentRequired object when unpaid). The cost and payment-failure behavior are exactly the kind of detail annotations cannot express.

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 with the 'Use when' trigger, then flows through input, return values, index behavior, and pricing in a single dense paragraph with no filler sentences. It is long and somewhat run-on, but every clause carries operational information.

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, so the description carries the return-value burden and does so: it names the fields returned (page URLs with lastmod, changefreq, priority) and the sitemap-index case. Combined with the discovery order and payment model, an agent has everything needed to call and interpret this tool.

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 coverage is 100%, so baseline is 3, but the description adds real meaning: it clarifies that 'url' accepts either a site URL (triggering discovery) or a direct sitemap URL, and explains what expand does for a sitemap index ('returns its child sitemaps and (expand=true, default) the URLs of the first child sitemaps up to the limit'). It goes beyond restating the schema.

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: returns the list of pages a site publishes, in the form of sitemap URLs with lastmod/changefreq/priority. This is clearly distinguishable from siblings feed, links, meta, and read, which cover RSS, link extraction, metadata, and page content respectively.

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?

Opens with an explicit trigger: 'Use when you need the list of pages a site publishes (to crawl it, find recent posts, or audit SEO)', giving three concrete scenarios. It does not, however, name or contrast with the sibling tools (feed, links) that an agent might otherwise reach for.

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