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

With no annotations, the description carries the full burden and does well: it discloses that the call is mutating, consumes the per-user zone quota, provisions on a hosting node, and auto-wires delegation for site domains. It omits permission/auth requirements and failure modes, but the operational side effects are covered.

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 dense sentence with the resource and the parameter-choice constraint front-loaded; every clause earns its place. It is slightly overloaded with the provisioning/delegation clauses, but there is no wasted text.

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 two-param create tool with no annotations and no output schema, the description covers creation modes, quota cost, and delegation side effects. It stops short of describing the return value or the required caller permissions, which an agent would still want.

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 0%, so the description must compensate, and it does: domainId is tied to a site-registered domain, externalFqdn to an external one, plus the mutual-exclusivity constraint. It does not add format details (uuid, 253-char max, error behavior when both or neither are supplied), leaving a small gap.

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 ("Create a DNS hosting zone") and immediately distinguishes the two input modes an agent must choose between. It is unambiguous against siblings such as dns_zone_get, dns_zone_delete, and dns_record_create without needing their schemas.

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 specifies the selection rule "exactly one of the two" and explains which input path applies to which scenario (site-registered domain vs external domain). It gives clear context but does not address when to prefer this over related tools like domain_register or dns_record_create.

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