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

Annotations already declare read-only, open-world, non-destructive behavior, but the description adds useful operational context: the 4xx missing-file behavior, the returned fields, pricing, failed-call charging, and repeat-call cost. This goes well beyond what the annotations provide and does not contradict them.

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 definition is front-loaded with the purpose, rule semantics, return values, and usage guidance. It is mostly efficient, though the pricing sentence and the later 'each call is charged' clause are somewhat redundant.

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 still explains the return fields and the missing-robots.txt edge case. Combined with the fully documented two-parameter schema and the annotations, an agent has enough information to invoke it correctly.

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 'url' and 'agent' are already documented in the input schema. The description provides an example URL and mentions crawler/user-agent rules, but it does not add much parameter meaning beyond the schema descriptions.

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 specific verb and resource: 'Read a site's robots.txt and say whether a crawler may fetch a URL.' It also distinguishes the tool from the related sitemap use case, so an agent can identify it 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?

It explicitly says to 'Use before scraping or crawling a site politely' and routes sitemap URL exploration to the separate sitemap tool. The missing-robots.txt behavior is also stated, giving clear context for when the tool applies.

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