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

Beyond the annotations, the description discloses the external data sources queried, the read-only/no-action/no-persistence posture, and limited caching. It also resolves the apparent tension between 'deterministic' and idempotentHint=false by explaining that external evidence may change between calls — context the annotation alone would leave confusing, though the response shape is left to the output schema.

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-loaded with the decision outcome and behavior, then labeled USE WHEN / DO NOT USE WHEN sections and a concrete example. Dense but every clause contributes routing or behavioral information; no filler.

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 decision tool with a full output schema and rich annotations, the description covers purpose, exclusions, data provenance, side-effect profile, and volatility caveat. Nothing an agent needs to select or call it 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?

Schema coverage is 100% and the schema itself already spells out the bare-hostname constraint, rejection of localhost/IP literals, and length cap. The description adds only a worked example ('domain=example.com'), which is marginal value over the schema — baseline 3 applies.

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 names a specific verb and resource ('domain risk and trust evaluation'), states the decision vocabulary (ALLOW / REVIEW / BLOCK), and enumerates the evidence sources used (DNS, RDAP, TLS, HTTP/redirect, URLhaus, local indicators). An agent can distinguish it from siblings like domain_agent_discovery_check 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 USE WHEN (interaction, onboarding, outreach, payment) and DO NOT USE WHEN clauses that name the correct alternative tool for each excluded case (domain_agent_discovery_check for health inspection, email_suitability_decision for email validation). Routing is fully determined.

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