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

With no annotations, the description carries the full burden and does so: it discloses the email-confirmation prerequisite, the 30-day reaping consequence, the atomic claim+record coupling, and the meaning of 400/503/409 responses. This is exactly the mutating-operation context an agent needs before writing.

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?

Five sentences, each carrying distinct load: what it does, the email prerequisite, the return shape, the atomic failure mode, and the 409 semantics. Nothing is redundant and the scope statement is front-loaded.

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?

There is no output schema, so the description supplies the return contract ('returns the fqdn and, when a record was requested, the created record') plus error-mode behavior. For a 6-parameter mutating tool with no annotations, it covers everything needed to invoke correctly.

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, but the description adds real meaning: 'email' is conditionally required on first registration, 'domain' selects which suffix the label lives under, and 'host'/'type'/'content' are bound together as one optional first record. The coupling of these parameters is not obvious from the schema alone.

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 ('register a subdomain on this account') and immediately scopes it with concrete examples of the naming space (label.makes.fyi / label.agentdomains.co). It is clearly distinct from siblings like add_dns_record (record-only) and check_availability (read-only).

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 routes the agent between claim_domain and attach_email ('pass email here or call attach_email first'), and gives a decision rule for the 409 case ('carry on using it, not pick another label'). It also states the retry condition for malformed/refused records.

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