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

Annotations declare readOnlyHint=true, idempotentHint=true, and openWorldHint=true, which already cover safety. The description adds the method (DNS brute-force enumeration) and lists return fields (subdomain names, record types, IPs, status), providing helpful behavioral context beyond what annotations convey.

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?

Two sentences front-load the action and output, then add use cases. No wasted words; efficiently conveys all necessary information.

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 an output schema (inferred from context signals), the description need not detail return values but does so anyway. It explains the method, output fields, and use cases. For a single-parameter tool, this is 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?

The only parameter (domain) has full schema coverage (description: 'Domain name to discover subdomains...'). The description reinforces purpose but does not add new parameter-level details. Baseline 3 is appropriate since schema already does the job.

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 that the tool discovers subdomains via DNS brute-force enumeration. It distinguishes itself from sibling tools like whois.dns.lookup (which retrieves DNS records) and whoisjson.ssl.check (for SSL) by specifying the technique and output.

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 use cases: security reconnaissance, asset inventory, infrastructure mapping. While it doesn't explicitly exclude alternatives, the context of sibling tools makes it clear when to use this over other DNS tools. Slight gap in explicit 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.