Subdomains

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

Goes well beyond the annotations (readOnly/openWorld/idempotent/destructive) by disclosing that two sources are queried in parallel, that the first responder's result is returned (non-deterministic provenance), and that failure of both sources yields an error instead of a silent empty list. The failure-mode disclosure is exactly the kind of context annotations cannot carry.

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 sentences, each earning its place: what it does and how, what it is for, and how it fails. The most important information (mechanism and source) is front-loaded.

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?

With an output schema present, return values need no explanation, and the description still covers mechanism, provenance, intended use, and failure behavior. Nothing an agent needs to call this correctly is missing.

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?

Only one parameter with 100% schema description coverage ('Registrable domain, e.g. stripe.com'), so the schema already does the work. The description adds the notion of public subdomains of a domain but no format or edge-case detail beyond the schema, making the baseline 3 appropriate.

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 ('Discover a domain's public subdomains') and names the exact data sources (Certificate Transparency logs, crt.sh, Cert Spotter). This is specific enough to separate it from siblings like dns_lookup or domain_intel, which would not be CT-log based.

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 clear usage context ('useful for mapping a company's public attack surface or infrastructure'), which tells the agent when this tool is a good fit. It does not name an alternative or a when-not condition, so it falls short of a 5.

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