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

Beyond the annotations, the description discloses that validation exactly matches the Studio subdomain field, that replacement takes effect immediately, that there is NO redirect, and that the previous subdomain is released for anyone to claim. It also notes passing an empty string clears it. These are non-obvious side effects an agent must know, going well beyond the structured hints.

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 sentences with the main action front-loaded, followed by high-value side effects and a routing note. There is no filler or repetition of schema content. Every clause earns its place.

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 2-parameter setter with no output schema, the description fully covers validation parity, immediate effect, absence of redirect, release of the old subdomain, clearing behavior, and the alternative tool. Nothing essential is missing for an agent to invoke it 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?

Both params are fully described in the schema (100% coverage), so the baseline is 3. The tool description adds background context about the subdomain's role in the hostname but does not add syntax or format details beyond the schema. No param-level information needs compensating.

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?

The description opens with a specific verb phrase 'Set or clear the app platform subdomain', naming both the action and the resource, and defines the exact meaning via the '<subdomain>.<base domain>' host pattern. It also explicitly contrasts with add_custom_domain, preventing confusion with sibling tools. This is a model of purpose clarity.

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 explicitly states when not to use this tool: 'For a domain the user owns, use add_custom_domain instead.' It also clarifies the clearing behavior via an empty subdomain, giving an agent the full decision context for set versus clear. The alternative is named directly, satisfying the 'explicit alternatives' bar.

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