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

Annotations already declare readOnly/openWorld/non-destructive, so the description's added value is the plan gating and the per-domain quota accounting — genuine behavioral facts not in structured data. It stops short of describing batch failure semantics (e.g. whether one bad domain fails the whole call), but covers the commercially important behavior well.

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?

Two sentences, zero filler, with the core action front-loaded and the plan/quota caveat second. Every clause earns its place.

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 three-parameter read tool with no output schema, the description plus rich schema descriptions and annotations cover calling correctly. The notable remaining gap is return/error shape for partial batch failures, which 'normalized RDAP registration data' only hints at.

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 description coverage is 100%, so whois, follow, and domains are already fully documented in the schema, including the 1-10 limit and IDN handling. The description adds nothing parameter-specific, making the baseline 3 the correct score.

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 ('Look up normalized RDAP registration data') plus the batching scope ('several domain names in one pooled call'), which is exactly what separates it from the sibling domain-lookup. An agent can pick between single and bulk 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?

Gives real eligibility and cost context (requires Pro or Business plan; each domain counts against quota), which is useful pre-call guidance. However, it never states when to prefer this over domain-lookup for a single name, or when-not to batch, so alternative selection is left to inference.

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