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

Adds substantial context beyond the annotations: auth requirement (full_access key), global name uniqueness, plan-based quotas, the exact contents of the returned DNS records (three DKIM CNAMEs, MAIL FROM MX and SPF TXT), and propagation timing (minutes to hours). None of that is derivable from readOnlyHint=false / idempotentHint=false.

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?

Front-loads the operation and the returned records, with constraints and next steps following in a sensible order. The DNS record list is stated twice (paragraphs one and three), which is minor redundancy that could be trimmed.

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?

No output schema exists, so the description carries the burden of describing the return value — and it does, enumerating the DNS records and warning about propagation delay. Prerequisites, quota limits, and the verify/get follow-up chain close the loop for a mutation tool.

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%, so the baseline is 3; the description earns one above by explaining that the MAIL FROM subdomain is what receives the MX/SPF records (illuminating custom_return_path) and that a domain is attributed to a tenant. It does not address the region parameter, which is left entirely to the schema.

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+resource ('Create a domain', 'Registers a domain and returns the DNS records') and immediately distinguishes it from get_domain/list_domains/update_domain by describing the write and its return payload. An agent can tell exactly what this does without opening the 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?

Explicitly prescribes the follow-up sequence ('afterwards call verify_domain and then get_domain') and states the prerequisites (full_access API key, plan ceilings Free 3 / Pro 10 / Scale 1,000). It lacks an explicit exclusion against update_domain for existing domains, but the create-only framing plus downstream routing is strong context.

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