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

Annotations cover the safety profile (readOnly, idempotent, non-destructive), and the description goes well beyond them: cache behavior and hourly refresh, stale-feed handling, the exact pricing model ($0.02 USDC via x402 in _meta), and that errors are not charged. It also warns that leak-site claims are unverified attacker assertions. This is rich behavioral disclosure.

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 is dense and fairly long, but it is front-loaded with the core question and each subsequent clause carries distinct information (mechanism, verdicts, caveat, failure/pricing). No filler sentences; slightly heavy for a single-parameter tool.

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 no output schema, the description compensates by enumerating the return verdicts (listed, claimed, listed_and_claimed, no_known_threat) and the matching reports. Error/payment semantics are fully covered, so an agent has everything needed to invoke and interpret the tool.

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?

With one parameter at 100% schema coverage the baseline is 3, but the description adds real meaning: it explains that the input hostname is resolved (A/AAAA) and matched both as the name, its parent domains, and resolved IPv4, clarifying what form of input is accepted and how it is used.

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 opening question plus the mechanism sentence state a specific verb (check/resolve/match) and resource (domain against IOC feed and leak-site claims), so an agent knows exactly what this does. However, it never differentiates itself from the obvious sibling bulk_threat_check, leaving the single-vs-bulk choice implicit.

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?

Usage context is implied (look up whether a domain is known-bad) and the caveat 'No match is not proof of safety' usefully frames interpretation. But there is no explicit when-to-use/when-not or named alternative, and the sibling bulk_threat_check for multi-domain cases is never mentioned.

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