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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds value beyond that by disclosing the returned payload shape and situating the call in the add/configure/verify workflow. It does not mention auth requirements or error behavior, keeping it 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?

Front-loaded with the when-to-use condition, then return contents, then the sibling routing. Roughly three dense sentences, each earning its place. Slightly long on the lifecycle narration, 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?

No output schema exists, so the description carries the return-value burden and does so by listing hostnames, DNS instructions, stage proxy targets, fallback IPv4 addresses, and next steps. Combined with the annotated safety profile and the workflow guidance, an agent has everything needed to call and interpret this 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 single app_id parameter is fully documented with a description in the schema. The description only implies an app scope ('for an app') without adding format or syntax detail. Baseline 3 is appropriate when the schema does the work.

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: returning setup guidance and current custom domain status for an app. It further enumerates what comes back (hostnames, DNS instructions, proxy targets, IPv4 addresses, next steps). This cleanly separates it from add/delete/verify siblings, which it names directly.

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 gives the trigger ('when you need setup guidance or to check the current custom domain status') and routes the agent through the full lifecycle: add_custom_domain to attach, then verify_custom_domain to activate, and delete_custom_domain to remove. The alternative tools are named with their conditions, leaving little to inference.

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