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

Annotations already declare readOnlyHint/idempotentHint, so the safety profile is covered, and the description adds genuinely new behavior: polling semantics, expected status transitions and timing, the capability_locked gating response with a next step for the user, and the fact that the record may take minutes to propagate. That is exactly the context an agent needs to avoid misinterpreting a pending status as failure.

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 purpose and polling instruction, then preconditions, then a compact Args/Returns block. Slight redundancy in restating the response_format default that the schema already declares, but the Returns section earns its place since no output schema exists.

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?

With no output schema, the description's inline Returns shape (custom_domain with domain, status, dns_records, certificate, checks, failure, last_checked_at) is necessary and provided. Prerequisites, polling behavior, and the locked-state response are all present for a read-only tool of this complexity.

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 description coverage is 100%, so the schema already fully documents agent_key and response_format; the description's 'Args' line merely restates the response_format enum and default. Baseline 3 applies because the schema carries the parameter burden and the description adds nothing beyond it.

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+resource ('Read the help center's custom domain') and then enumerates exactly what is returned: the domain, the DNS record to add, and the status. This is clearly distinguishable from the sibling mutators helpcenter_set_custom_domain and helpcenter_remove_custom_domain.

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 says to poll it while the user sets up DNS and describes the status progression (pending_dns → verifying → issuing_certificate → live, usually minutes). It also names the preconditions (claimed help center, verified email, active plan) and routes to helpcenter_get_help_center for the capability_locked case, so the when-to-use and when-not-to-use are both covered.

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