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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely non-derivable behavior: a free-tier quota of 10 calls/day, per-call pricing beyond it, and the two payment paths (params._meta["x402/payment"] or X-API-Key credits). It does not describe failure modes (e.g., unreachable robots.txt) or result-shape caveats, keeping it at 4.

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?

The lead question is front-loaded, followed by capability detail, then commercial terms — a logical order with little filler. The trailing origin tag "[served by tools.moneytools.dev]" is the one element that doesn't serve selection or invocation, and the pricing sentence is dense but necessary for a paid endpoint.

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, annotations covering safety, and full parameter documentation, the description only needs to convey purpose, standard, and access terms — which it does. The marginal gap is that it never states how to interpret a deny or what happens when robots.txt is missing, which an agent would want before relying on the answer.

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 100% for both parameters, so the schema already explains url and userAgent including the '*' default. The description's only added semantic is that the allow/deny table spans 12 AI crawlers, which hints at the meaning of the userAgent argument without adding format or matching rules. 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?

The description opens with a precise framing question ("May this user agent fetch this URL?") and names the concrete operation: RFC 9309 robots.txt evaluation with the matching rule, crawl-delay, sitemaps, llms.txt presence and a 12-crawler allow/deny table. The verb+resource is unmistakable and the output contents are enumerated. It stops short of distinguishing itself from the adjacent sibling llms_txt_validate, which is why it isn't a 5.

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?

Usage is only implied — an agent can infer this is the pre-crawl permission check — but there is no explicit when-to-use/when-not statement and no routing to alternatives such as llms_txt_validate or broken_links. The only explicit conditional guidance concerns billing thresholds (10 free calls/day, then $0.001/call), which is cost guidance rather than tool-selection guidance.

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