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

Annotations already declare readOnlyHint=true and openWorldHint=true, and the description adds substantial behavior beyond that: the two-source query chain with fallback, the 100-name cap, the 10-second timeout, the caveat that a log name is not proof the host still exists, and the full status response contract. It even tells the agent how to interpret not_applicable versus error, which is critical for correct action.

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 front-loads the core purpose in the first sentence, then packs each subsequent sentence with non-redundant operational detail: fallback behavior, limits, interpretation caveat, and return-status semantics. Every sentence earns its place; there is no filler or repetition of schema or annotation content.

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, read-only tool with no output schema, the description is unusually complete. It covers the data source, failure fallback, scaling caps, timeout, and a full enumeration of possible status values with their semantic meanings. An agent has everything needed to invoke the tool and interpret the result correctly.

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 description coverage is 100%, so the schema fully documents the domain parameter, including what is rejected. The tool description adds nothing about the parameter itself, which is fine because the schema already carries that burden. Per the baseline rule, a 3 is appropriate when the schema does the heavy lifting.

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 a specific verb and resource: 'List subdomains of a domain that appear in Certificate Transparency logs.' This clearly distinguishes it from sibling DNS and web-surface tools by naming the data source (CT logs) and the exact output (subdomain names). The additional 'map what hosts a domain has exposed' phrasing reinforces the intent without ambiguity.

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 states a concrete use case: 'Use to map what hosts a domain has exposed through the certificates issued for it.' It also clarifies behavioral context (fallback from crt.sh to certspotter, caps, timeout) that helps an agent decide when this is appropriate. It does not explicitly name alternatives or exclusion criteria, but the use case is clear enough for routing among the sibling tools.

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