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

Goes well beyond the annotations by disclosing how the lookup resolves (IANA bootstrap selection), how availability is inferred (RDAP 404), the exact fields returned for registered names, the DNS NS fallback for non-RDAP TLDs, subdomain flagging, and — critically — the paid x402/Solana billing model at $0.005 per successful call. Cost and payment requirements are exactly the kind of behavioral context annotations cannot convey.

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?

Four tightly packed sentences with the core purpose and limits first, then result semantics, then fallback, then pricing and the HTTPS mirror. Every clause earns its place, though the density borders on telegraphic and the pricing/endpoint sentence could be split for readability.

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, no-output-schema tool, the description supplies the return-field inventory (registrar, IANA id, dates, status, nameservers), the availability signal, the TLD fallback path, and payment terms — everything an agent needs to call it and interpret the response without opening a schema.

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 already specifies comma-separated input, max 20, ASCII/punycode, and the 'domain' alias. The description only restates the 20-domain cap, adding no format or edge-case detail (e.g., how invalid or duplicate entries are handled). Baseline 3 is appropriate when the schema carries the parameter burden.

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 — bulk domain availability via authoritative RDAP lookup — with the operational scope (up to 20 domains) front-loaded. It is clearly distinguishable from siblings like domain_intel, rdap_age, and dns_dump because it frames itself as a registry-authoritative availability check with per-domain result fields.

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?

The bulk framing and 'up to 20 domains' limit imply when this tool applies, and the RDAP/DNS-fallback note tells the agent how results are derived. However, no sibling is named (e.g., domain_intel for richer intel, rdap_age for single domain age) and there are no explicit exclusions or when-not-to-use conditions.

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