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

Annotations already declare readOnly, closed-world and idempotent, yet the description still adds substantive context: it is answered from synced IANA and root-zone data, makes no network call, is instant, and fields without data are omitted rather than guessed. It also scopes negatively by naming two fields deliberately absent (registry operator, delegation date), which prevents false expectations.

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?

It is front-loaded: contents first, then usage, then behavior, each in its own paragraph. The one weakness is the very long first sentence, which packs six field groups into a single clause chain and costs more reading effort than a short bulleted list would.

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?

With a single parameter, an output schema carrying the return shape, and annotations covering safety, the description supplies exactly the remaining pieces: data provenance, offline behavior, omission policy, scope exclusions and the sibling alternative. Nothing an agent needs to 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 description coverage is 100% and the single tld parameter is fully documented there, including examples, leading-dot tolerance and the punycode/unicode case. The description adds no parameter-level meaning beyond that, so the baseline of 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 first sentence names a specific verb and resource ('facts about one top-level domain') and enumerates exactly which facts are returned (delegation, type, RDAP server, name servers, DS/DNSSEC, Web3 namespace collisions). The closing line of the usage paragraph explicitly separates it from the sibling lookup_target, so the agent can distinguish it without opening the 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?

Three concrete use cases are given ('where to send an RDAP query for a TLD, whether a TLD is signed, or whether a name under it could mean something else on a blockchain') plus an explicit redirect: 'For one domain use lookup_target instead.' That is when-to-use plus the alternative, nothing left to inference.

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