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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety bar is low. The description still adds real value beyond them: 'Passive only' (no traffic touches the target) and a full inventory of what the response contains — counts, examples, rationale, naming clusters, issuers, wildcards, and 10 newest names.

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 first clause front-loads the action and source, followed by the output inventory. The category enumeration is long but each item conveys what an agent will actually receive, so it largely earns its place; it could be trimmed without loss.

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?

There is no output schema, so the description must describe the return payload — and it does so thoroughly, listing every grouping dimension and supplementary section. Missing only the response shape/ordering and pagination or size limits, which matters for consumers of large domains.

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%, including the source fallback chain and include_expired semantics, so the schema already carries parameter meaning. The description adds nothing about domain normalization, source selection, or the cost tradeoff of expired certificates beyond what the schema states. Baseline 3 applies.

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 (reads subdomains from certificate transparency) and immediately qualifies the value-add: grouping for recon triage. The enumerated group categories make it clearly a summarization tool rather than a raw enumeration tool. It never names a sibling to contrast with, so the boundary with find_subdomains must be inferred.

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 trailing 'Passive only' signals the operating mode, which is a useful selection hint versus active-resolution siblings. However, there is no explicit when-to-use, when-not-to-use, or named alternative (e.g., 'for a raw name list use find_subdomains'). Usage must be inferred from the purpose statement.

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