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

Well beyond the annotations (which only say it is a non-read, non-idempotent, non-destructive, closed-world write), the description discloses that custom creation spawns a DNS zone and that the returned ns_servers must be configured at the registrar before verification succeeds. That is a non-obvious side effect plus a required follow-up step, exactly the kind of behavior an agent cannot infer from structured fields.

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 tight sentences, no filler. The core action comes first, the mode distinction next, and the operational caveat last, which matches the order an agent needs to reason about the call.

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 write tool with no output schema, the description covers the important gaps: what each mode creates, the async registrar step, and the ns_servers return field. It omits permission/subscription prerequisites and gives no guidance on dns_provider_id, which is a minor but real gap.

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 baseline is 3, but the description earns more by explaining what the enum values actually produce (system = free random subdomain, instant; custom = owned domain requiring DNS), and by tying the name parameter to the custom case only. dns_provider_id is still left to the schema, with no hint of when it matters.

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?

"Add a tracking domain" gives a specific verb and resource, and the next two sentences split the operation into its two concrete variants (system vs custom), so an agent knows exactly what will be created. It does not name sibling tools such as update_domain or list_domains, so differentiation from the rest of the domain family is implicit rather than stated.

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 clearly states the decision rule between the two modes: system for a free random subdomain that works immediately, custom for a domain the user already owns and must be verified via NS records. It also includes an explicit exclusion ("Buying a domain is panel-only"), which prevents a misuse. It stops short of routing the agent to alternatives like update_domain or list_domains.

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