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

Annotations only declare readOnlyHint=false, so the description correctly signals a mutation and adds real value with the confirm-gating note ('previews until confirm: true') and the return payload. However it omits what happens on an already-connected domain, whether domain verification is required, and who is authorized to call it.

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?

Two compact clauses, front-loaded with the action and the immediate result, then the confirm-gating caveat. No redundant restatement of the name or title.

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 mutation tool with no output schema, the description does state the return value (DNS records), which offsets part of the burden. But it leaves out follow-up behavior (verification/refresh), error conditions, and hostname requirements, which matter for a 3-param domain-connection operation.

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 67%: organizationId has a source hint and confirm explains the preview/execute switch, but hostname is undocumented in both places. The description adds no format guidance for the hostname (bare FQDN, no scheme, min length 3), so the remaining gap is not compensated.

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?

Specific verb+resource ('Connect a custom domain to a gym's public page') plus the outcome ('returns the DNS records to add'). The 'gym' scoping implicitly distinguishes it from connect_my_custom_domain, but the sibling is never named, so differentiation relies on inference.

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?

Usage is implied by the name and the gym scoping, but there is no explicit when-to-use guidance: no mention of prerequisites (org admin rights), no pointer to get_gym_custom_domain to check current state, and no routing away from connect_my_custom_domain or refresh_gym_custom_domain.

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