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

Annotations cover the read-only/idempotent/no-destruction profile, and the description adds substantial extra context: DNS resolution is performed on each domain and the resolved IPv4 is also matched, the feed is 30-day high-confidence IOC, no ransomware lookups, a stale feed returns an error, and billing terms ($0.50 USDC per call, not charged on stale/invalid/upstream failure, payment in _meta['x402/payment']).

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?

Dense but appropriately sized: three sentences covering scope, sibling routing, feed behavior, and billing. Slightly packed with billing/wrapper details, but every clause earns its place and the core capability 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?

For a single-param, no-output-schema tool, the description covers scope, limits, sibling alternatives, resolution behavior, feed freshness, failure modes, and payment mechanics. An agent has everything needed to invoke it correctly and interpret billing consequences.

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%, so the schema already documents items as 'Up to 100 domains/IPv4, comma or newline separated' with maxLength 20000. The description repeats the 'up to 100 domains or IPv4' limit but adds no new syntax or format detail. Baseline 3 is appropriate when 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?

Specific verb+resource+scope: 'Check up to 100 domains or IPv4 addresses at once against ThreatCluster's high-confidence 30-day IOC feed.' It explicitly distinguishes itself from the sibling threat_check ('use threat_check for one domain'). An agent can route between the two without opening either schema.

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?

Explicit when-to-use (bulk domains/IPs) and when-not (single domain -> threat_check; ransomware claims not supported). Also states that stale feed and invalid input return errors with no charge, giving clear operational boundaries.

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