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

Adds substantial consequences beyond the annotations: name/organization/email edits trigger registrant verification and can impose a 60-day inter-registrar transfer lock, and accepted changes report as verification pending. This tells the agent why the destructive flag matters and what the caller commits to, which annotations alone (destructiveHint, non-idempotent) cannot convey.

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?

Four sentences, each carrying a distinct fact: purpose, contact_handle behavior, verification/lock consequence, and the resulting status. The core scope is front-loaded and nothing is repeated from the schema.

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?

An output schema exists, so return values need not be described, and the high-stakes verification/lock behavior is well covered. The remaining gap is update semantics for the many optional fields—whether a partial payload replaces or clears existing contact data—which an agent needs before mutating a registrant record.

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 0% across 13 parameters, and the description only explains three of them: contact_handle's apply-without-copy semantics, acknowledge_transfer_lock's gating role, and which fields trigger verification. It leaves ten address/phone fields undocumented, including whether omitted fields are preserved or cleared, so it only partially compensates for the coverage gap.

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 ('Update the registrant contact') with explicit scope ('a domain owned by the authenticated customer'). It also distinguishes the mode of operation from contact creation, noting that passing contact_handle applies an existing reusable contact rather than copying fields into a new record, which separates it from create_contact.

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?

Gives concrete conditions: pass contact_handle by itself to reuse an existing contact, and set acknowledge_transfer_lock=true when changing name, organization, or email. It does not explicitly name sibling tools like create_contact or list_contacts as alternatives, so the routing guidance is implied rather than stated.

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