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

Annotations already declare the write/non-idempotent/open-world profile, and the description usefully adds beyond that: the app is left in a 'pending DNS state', DNS instructions are returned, duplicate hostnames are rejected, and routing only activates after a separate verify call. It doesn't cover failure modes or rollback, keeping it just short of a 5.

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?

Four short sentences, front-loaded with the core action and scope, each contributing distinct information (state, requirements, rejection rule, next step). Slight redundancy with the schema enum values, but 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 write tool with full annotation coverage, complete schema, and only three params, the description covers the action, resulting state, constraints, and the required follow-up call. No output schema exists, yet return content (DNS instructions) is still summarized, so nothing essential is missing.

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% with all three params (including the enum) documented in the schema itself. The description repeats the dns_mode enum values but adds no syntax, format, or constraint detail beyond what the schema provides, matching the baseline for fully documented params.

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 (attach) and resource (a new hostname/domain to a deployed app), and clarifies the resulting state (pending DNS) plus what it returns (DNS setup instructions). It also implicitly distinguishes itself from verify_custom_domain and get_custom_domain_instructions.

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 names the follow-up tool (verify_custom_domain) and the condition that triggers it, states the required dns_mode values, and gives an exclusion (hostnames already registered are rejected). An agent knows exactly when to call this and what to do next.

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