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

Annotations cover the safety profile (readOnlyHint, openWorldHint), and the description adds critical behavior beyond that: the $0.01 USDC x402 cost, that calling it returns HTTP request plus payment requirements, and that an x402 client is needed to actually get data. That payment flow is material and normally would not be discoverable otherwise.

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?

Four tight sentences with the cost and purpose front-loaded and no filler. It is on the dense side but every sentence (purpose, returns, payment mechanics) earns its place.

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 enumerating the return fields (allowed, matched rule, crawl-delay, sitemaps) plus the payment requirement. What remains unstated (rate limits, failure/error modes when robots.txt is absent) is minor.

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 both parameters (url, ua with default '*') are already documented in the schema. The description's 'for a given user-agent' aligns with the ua parameter but adds no syntax or format detail beyond it, so the baseline 3 applies.

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: 'Check whether a URL may be crawled per the site's robots.txt for a given user-agent.' This is clearly distinct from siblings like link_check, page_check, and page_meta, which probe other aspects of a URL.

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 description explains what the tool does but gives no when-to-use guidance, no exclusions, and no routing to alternatives among the many sibling tools. The agent must infer context from the purpose statement alone.

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