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

Annotations already declare readOnly/non-destructive/closed-world, so the safety profile is covered. The description adds genuinely useful non-annotation context: the quota exemption for metadata calls, and the shape of the per-TLD answer (RDAP server, support-since date, per-field fill rates).

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?

A single front-loaded sentence carries the purpose, both modes, the return content, and the quota caveat with zero filler. The dense colon-list is still readable, and the most decision-relevant fact (metadata, no quota cost) lands before any elaboration.

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 zero-required-parameter, fully documented listing tool with no output schema, the description covers purpose, both operating modes, and quota behavior. The only modest gap is that the exact list output shape (names only vs. richer objects) is implied rather than stated, though the schema hints at 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?

Schema coverage is 100% and all three optional parameters are already documented in-schema with examples and precedence rules, so the description need not compensate. It restates the omit-to-list behavior but adds no syntax or format detail beyond the schema, warranting the baseline.

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 names a concrete resource (TLDs this API supports) and a concrete verb, plus two distinct modes: enumerate the set or describe a single entry. That scope is clearly distinct from every sibling (domain/ip/asn/entity/nameserver lookups), which all query records rather than enumerate API metadata.

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?

It gives clear mode-selection guidance — pass nothing to list names, or supply one TLD to describe it, with the schema reinforcing that `since` and `server` are filters ignored when `tld` is set. It stops short of naming an alternative or any when-not-to-use condition, so no explicit routing.

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