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

Beyond the readOnlyHint annotation, it adds 'Read-only; files nothing' and 'A lookup, not legal advice; it does not guarantee removal'. It also discloses distinct behavior for direct hosts vs proxied domains, giving the agent robust expectations about results and limitations.

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 description is front-loaded with the primary purpose and each sentence contributes unique value: scope, specific identifiers, behavior variations, and caveats. It is detailed yet concise, with no wasted words.

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?

Given that an output schema exists and annotations already declare read-only and open-world nature, the description sufficiently covers purpose, behavior, and limitations. It also addresses edge cases (proxied vs direct hosts) and sets expectations, making it complete for the tool's complexity.

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?

The input schema fully describes the only parameter 'url' as 'The infringing URL or bare domain' (100% coverage). The description does not add details about URL format or examples, so it adds no semantic value beyond the schema. Baseline 3 is appropriate.

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 the specific verb-resource pair 'Look up who hosts a URL and where an abuse/takedown notice would go', making the tool's purpose immediately clear. It further specifies outputs (CDN/proxy, platform, direct host, abuse contact), distinguishing it from action-oriented siblings like 'start_takedown' and 'preserve_evidence'.

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 provides context for when to use this lookup tool versus proceeding to a takedown: it explains that for proxied domains it states that revealing the true host requires initiating an abuse report, implying a next step. However, it does not explicitly name alternatives or provide clear 'when not to use' guidance.

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