Add domain

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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely new behavior: the external DNS precondition and the 409 rejection path, which is consistent with idempotentHint=false. It does not mention auth/permission requirements or what a successful call returns.

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?

Three short sentences, each doing distinct work: what it does, the precondition with the helper tool, and the duplicate error. The purpose is front-loaded and there is no filler.

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 single-parameter mutation tool with no output schema, the description covers the operational essentials an agent needs: the external DNS prerequisite and the duplicate-domain failure mode, while annotations cover the safety profile. Missing only secondary details such as permission requirements and the success response shape.

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?

There is a single parameter with 100% schema description coverage including a pattern, minLength, and an example.com hint, so the schema carries the semantics. The description never mentions the 'domain' argument at all, adding no meaning beyond the schema; 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?

States a specific verb and resource ('Adds a domain to the account') and immediately distinguishes itself from the read-side sibling by pointing to get_domain_verification_key for the prerequisite. An agent can tell this apart from list_domains, get_domain, and delete_domain without opening any 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?

It gives a concrete precondition (the verification TXT record must already be in DNS) and names the tool that supplies it, plus the failure condition (409 if the domain already exists), which implicitly tells the agent not to call this for existing domains. It stops short of naming alternative tools for adjacent operations such as create_domain_pointer, so it is clear context without explicit exclusions.

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