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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), and the description goes well beyond them: pricing and per-call URL cap, the exact x402 v2 PaymentRequired error shape and retry path via params._meta['x402/payment'], the rule that invalid input and all-fail calls are never charged, the outbound User-Agent string, and the refusal of private/internal addresses. This is unusually rich behavioral disclosure.

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 core purpose, and each subsequent clause adds distinct operational detail (agent defaults, pricing, error handling, fetch policy). It is a dense single paragraph whose payment clauses run together, so it is efficient but not maximally scannable.

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 carries the burden of explaining results, and it does list what is returned per agent/URL (permission, crawl-delay, sitemaps, llms.txt). It stops short of describing the response shape or ordering, so it is nearly but not fully complete.

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 schema already documents urls, agents, and x402_payment, making 3 the floor. The description adds value beyond it by listing the default agent set (GPTBot, ClaudeBot, etc.) that applies when 'agents' is omitted, and by pointing to params._meta['x402/payment'] as the preferred payment location.

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?

The description names a precise verb+resource+scope: a 'crawl preflight' that checks whether each user agent may fetch each URL under robots.txt, with RFC 9309 longest-match and '*' fallback semantics spelled out. It is clearly distinguishable from siblings like url_status_check and sitemap_urls, and it enumerates the extra outputs (crawl-delay, listed sitemaps, /llms.txt presence).

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?

'Crawl preflight' frames the natural use case (run before crawling), and the payment tier rules (5 URLs per call, $0.001 USDC, when calls are/aren't charged) give concrete operating context. However, it never names a sibling it should be preferred over or states explicit when-not-to-use conditions, so it falls short of a 5.

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