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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint. The description reinforces these with 'Read-only. No side effects. Idempotent.' and adds extra behavioral info: daily quota, source (HackerTarget API), and 24-hour cache. No contradictions.

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 well-structured and front-loaded with the main purpose. It includes necessary details without redundancy. Every sentence adds value, covering purpose, constraints, use cases, quota, source, and fallback. It is slightly long but still concise for the information provided.

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 the tool has one required parameter, annotations, and an output schema (implied), the description covers all key aspects: purpose, input format, constraints, caching, quota, source, and a fallback mechanism. It is complete and leaves no obvious gaps for an AI agent to select and invoke this tool.

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 has one parameter with a description. The description adds value by explaining that if a domain is given, it is first resolved to its IPv4 A record, and that IPv6-only domains are not supported. This goes beyond the schema's basic description.

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 clearly states the tool's purpose: 'Find domains co-hosted on the same IP address (reverse IP lookup).' This is a specific verb ('find') and resource. It distinguishes well from sibling tools like domain_fetch_dns_records and domain_fetch_domain_history.

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 clear context for when to use the tool ('identifying shared hosting risk and mapping corporate infrastructure'). It also notes constraints (IPv6 not supported) and includes a fallback instruction to call report_feedback if needed. However, it does not explicitly state when not to use or compare with alternative tools.

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