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

Goes well beyond the annotations by disclosing billing semantics (invalid XML and execution errors uncharged, valid empty match charged), hard limits (512 KiB expanded, 1000 entries), supported encodings, and explicitly justifies the readOnlyHint=false annotation ('not marked read-only because each call is charged'). The price and free-tier details add decision-relevant context; the pricing detail is somewhat needlessly granular for a definition.

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 operation and the primary routing hint, and every sentence carries actionable information about limits, errors, or cost. The single dense pricing clause ('Price $0.002/call via x402 USDC or a card key (/credits), first 25 free; failed calls free') is useful but coupled with the read-only rationale, making the tail heavier than necessary.

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 an output schema present, return-format explanation is unnecessary, and the description covers everything else an agent needs: scope limits, encoding support, filtering, pagination, charging behavior, error handling, and the relationship to /extract. Nothing required to invoke it correctly is missing.

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 the baseline is 3, but the description adds real value above the schema: gzip support, substring filtering, pagination, and the 512 KiB/1000-entry caps that bound what offset/maxUrls can meaningfully reach. It does not, however, restate or clarify the case-insensitivity or 200-char constraint already in 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 ('Read one public XML sitemap or sitemap index as structured URLs and source-reported dates') plus scope boundaries that separate it from siblings like feed and extract. An agent can identify the operation 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?

Explicitly routes usage: 'Use to find which pages of a docs site to read before calling /extract,' naming the sibling it precedes. It also states exclusions ('Does not crawl pages or follow child sitemaps'), removing the main ambiguity an agent would face.

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