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

Annotations already cover the safety profile (readOnly, idempotent, open-world, non-destructive), but the description adds real behavioral substance: it refuses rather than guessing when a registry publishes no RDAP, requires no API key, and details the x402 pricing (free tier, prepaid header). These are invocation-critical facts an agent cannot derive from structured fields.

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 core question, then layered as returns → rationale → refusal semantics → input → pricing. Every sentence carries information, but the pricing and fraud-rationale passages make it longer than strictly needed for selection.

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?

Despite an output schema existing, the description correctly rounds out the agent's picture: what the verdict means, fallback behavior when RDAP is unavailable, and the payment/auth model. Nothing needed to decide whether and how to call it 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% with a single required 'domain' param, so the schema already carries the parameter. 'Required input: domain' restates it and adds no format guidance (e.g., whether URLs, subdomains or IDNs are accepted). Baseline 3 applies when the 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?

States a specific verb+resource and scope: registration age, expiry and registry status for any domain, sourced from RDAP. The GO/HOLD/STOP verdict framing makes the output's decision nature clear, distinguishing it from raw lookups like dns_lookup or ssl_check without needing to name them.

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 a concrete when-to-use context (invoice and vendor-impersonation fraud, changed payment details from a weeks-old domain), which is more than most definitions offer. It stops short of explicit when-not conditions or named sibling alternatives, so it lands at 4 rather than 5.

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