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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so safety is covered. The description adds genuinely new context with the '(Cost: 2 credits)' billing disclosure, which influences call budgeting, but it does not say what happens with an unrecognized or malformed TLD, whether any TLD is guaranteed to resolve, or whether results are cached.

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?

The core sentence is tight and front-loads what is returned, but it opens with a redundant 'TLD Lookup: TLD Lookup' prefix that merely restates the name and title. The cost note is well-placed at the end, but the definition as a whole contains one wasted clause and no structural separation between purpose and cost.

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?

This is a simple one-parameter read tool with full schema coverage, an output schema, and complete annotations, so most requirements are already met by structured fields. The description supplies the return semantics and the credit cost, leaving only edge-case behavior (invalid TLD) unspecified, which is minor at this complexity.

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%: the single 'tld' parameter is documented with a description and an example ('com'), including tolerance for a leading dot. The prose does not add any meaning beyond that, so the baseline 3 for schema-driven documentation is appropriate.

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 uses a specific verb ('retrieves') with a specific resource ('information about any top-level domain') and enumerates the fields returned (type, sponsoring organization). An agent can distinguish this from domain-adjacent siblings like WHOISLookup or DomainAvailability by the TLD-metadata framing, though it never explicitly names those alternatives.

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?

There is no when-to-use or when-not-to-use guidance, no mention of prerequisites such as passing the TLD without a leading dot vs. a full domain, and no routing away from overlapping siblings like WHOISLookup, DomainAvailability, or DomainAge. The only situational signal is the cost note, which tells the agent this is a paid call but not when to prefer it.

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