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

The description goes well beyond the annotations (openWorldHint=true, destructiveHint=false) by disclosing real behavioral traits: verification is what actually claims the hostname (first-to-verify-wins), success triggers global binding and certificate issuance, the server throttles rapid re-checks, and DNS propagation can take minutes. This is crucial context for a tool whose surface behavior ('check DNS TXT') could otherwise look read-only. No contradiction with annotations.

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?

Five sentences, each earning its place: purpose, call timing, non-polling instruction with rationale, monitoring alternative, and the claiming side-effect warning. It is slightly dense and longer than strictly necessary, but the content is high-value operational guidance rather than 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 one-parameter tool with a full output schema and complete parameter documentation, the description covers everything an agent needs to call it correctly: when to invoke it, how to handle the verified=false case, throttling behavior, how to follow up (get_custom_domain), and the side-effect of claiming the hostname. Return-value details are already handled by the output schema.

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% — the hostname parameter is already documented with a concrete example ('shop.customer.com'). The description reinforces that the hostname comes from create_custom_domain but adds no new format, constraint, or semantic detail beyond the schema. Baseline 3 is appropriate because the schema carries the parameter burden.

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 names a specific verb and resource: 'Check the DNS TXT challenge for a claimed domain' and states the consequential outcome ('take the global (hostname -> tenant) binding and start certificate issuance'). It clearly differentiates from the sibling family by referencing create_custom_domain as the source of DNS records and get_custom_domain as the status watcher, so an agent can tell verify_custom_domain apart from create/get/update/list_custom_domain without opening schemas.

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?

Explicit when-to-use guidance is given: 'Call this ONCE after the human confirms they have added the DNS records from create_custom_domain.' It also gives explicit when-not-to-use behavior ('do NOT poll this in a loop') and names the alternative tool for continued monitoring ('Read get_custom_domain to watch the certificate go from CERT_PENDING to ACTIVE'). Nothing is left to inference.

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