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

No annotations are provided, so the description carries the full burden: it correctly discloses that the method is passive with no traffic to the target and states the cost (1 credit per call). It does not mention result limits, pagination, or whether historical/expired certs are included, which are the remaining behavioral gaps.

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?

Three short sentences, front-loaded with the action and source, then safety context, then cost. No filler or restated title text.

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?

For a single-parameter lookup with no annotations and no output schema, the description covers what the tool returns (a list of subdomains), the passive safety profile, the authorization expectation, and the credit cost. It stops short of describing result shape or volume, which is the only notable omission.

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?

There is one parameter with 0% schema description coverage, but the schema's pattern and maxLength already imply a bare hostname rather than a URL, and the description's phrase 'of a domain' reinforces this. It adds only that modest clarification and no format examples.

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?

States a specific verb and resource (list subdomains) plus the exact data source (public certificate-transparency logs), which cleanly separates it from siblings like dns_lookup, domain_info, and reverse_dns that query different sources.

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?

Gives a clear use context (attack-surface mapping) and an authorization prerequisite ('domains you own or are authorised to assess'), but never names an alternative tool for the case where a live-DNS enumeration is wanted instead of historical CT data.

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