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

Goes well beyond the readOnly/openWorld/idempotent annotations by disclosing the hourly cache, that a stale feed errors and is not charged, that invalid input or upstream failure errors without charge, and the exact $0.01 USDC x402 cost with the payment field name. This is the kind of billing and failure semantics an agent needs before invoking.

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?

Front-loads purpose then layers returns, usage, caveat, and billing; every sentence carries information. It is dense and slightly long, but without an output schema the enumeration of return fields is necessary rather than padding.

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 correctly enumerates the return shape (listed/not_listed, match type, reason, linked reports/clusters). Combined with cache, error, and payment semantics, an agent has everything needed to call and interpret the result.

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?

The single parameter is fully documented in the schema (100% coverage), so the baseline is 3. The description adds one genuinely new nuance, that parent domains are also checked, but omits the schema's URL acceptance, so it neither compensates nor richly extends the schema.

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: checks a domain/parent domain/IPv4 against ThreatCluster's 30-day IOC feed and answers whether it is attacker infrastructure. The scope ('one domain or IPv4', 'high-confidence 30-day feed') cleanly separates it from sibling indicator_batch_check and the cve_*/group_* tools.

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 concrete usage contexts ('before opening a link, in email triage or SOC enrichment') and an important interpretive caveat ('Not listed is not proof of safety'). It does not name the batch alternative for multi-indicator workloads, so the single-vs-bulk routing decision is left implicit.

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