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

Annotations already cover safety (readOnly/idempotent/non-destructive), yet the description adds genuinely new operational facts: a 5,000-entry cap, that gzip sitemaps are NOT decoded (a real failure mode), and a per-call price of $0.008 USDC via x402 on eip155:8453. Cost and decode limitations are exactly the behavioral traits 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?

Three tight sentences: purpose and payload first, resolution behavior second, output shape and constraints third. No filler, no restatement of the title, and the cost caveat is placed last where it belongs.

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?

With no output schema, the description does the work of describing return values (page URLs with lastmod/changefreq/priority, or child sitemaps of an index), which is the critical piece. Minor gap: it does not say what happens when no sitemap is found or robots.txt is empty, which matters for an openWorld fetch.

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 carry parameter meaning. It clarifies that 'url' may be either a sitemap URL or a bare site URL, which is real added semantics, and 'Up to 5,000 entries' hints at the cap. But the 'limit' parameter (default 1000, min 1, max 5000) is never named or explained, leaving half the parameters undocumented.

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 ('Read a sitemap.xml') and immediately enumerates the payload (URLs with lastmod, child sitemaps), including the index-vs-page distinction. An agent can distinguish it from web_robots (which reads robots.txt) and web_extract without opening the schema.

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?

Gives explicit input-mode guidance: pass a sitemap URL directly, or pass a bare site URL and it will follow robots.txt-declared sitemaps then fall back to /sitemap.xml. That resolves the main ambiguity of what to put in 'url'. No when-not-to-use or named alternative sibling, so it stops short of 5.

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