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

With no annotations to lean on, the description carries the behavioral burden. It discloses that this is a metadata operation, that it will not consume the monthly quota, and what information it returns when describing a specific TLD. It does not detail response format or rate-limit behavior, but for a read-only metadata tool the disclosed traits are meaningful and sufficient.

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 with no filler. The primary action is front-loaded, the detailed return values are briefly summarized, and the quota-exemption note is a valuable standalone behavioral detail. Every sentence 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?

The tool is simple, has zero required parameters, and the schema covers all parameter semantics. The description fills the remaining gap by explaining what the response will contain in both list and describe modes, and it adds operational context via the quota note. Nothing material is missing for an agent to decide when and how to invoke it.

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?

All three parameters are already fully documented in the input schema, so the baseline is 3. The description adds useful context for the 'tld' parameter by naming the exact fields returned, but it does not add meaning for 'since' or 'server' beyond what the schema already provides.

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 clearly states the tool's dual function: list all supported TLDs or describe one with specific details like the answering RDAP server, support date, and field fill frequency. This is a specific verb+resource combination that distinguishes it from the sibling lookup tools, which all perform network/data lookups rather than API metadata discovery.

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 description gives strong contextual guidance by labeling the operation as metadata and explicitly noting it never counts against the monthly quota, signaling safe exploratory use. It does not explicitly name alternative tools or provide when-not-to-use conditions, but the framing clearly separates this discovery/metadata tool from the lookup-focused siblings.

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