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

Annotations already declare readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false, so mutation and network-reaching behavior are known. The description adds a genuinely useful non-schema fact — that the returned handle is reusable across multiple domains and how it is auto-generated when omitted — but says nothing about failure modes, required account/prepaid balance, or validation errors. Useful but partial beyond the 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?

Three sentences, front-loaded with purpose then prerequisites then the handle rule. Efficient, though sentence order puts the input-validation pointers ahead of the more consequential role-boolean semantics that go unmentioned.

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 explained, and the handle semantics are covered. However, for a 16-parameter creation tool with 0% schema description coverage, the description leaves the default_* role flags and the distinction between address and address_line_2, organization, and phone fields unaddressed.

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 16 parameters, and the description only explains the handle default-generation scheme. That is real added meaning for one important optional field, but nine required fields and the four default_* role booleans (default_admin, default_billing, default_technical, default_registrant) get no clarification at all, leaving a large gap for a 16-parameter tool.

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 (create) plus resource (reusable contact for domain registration) with the lifecycle role made explicit — the handle feeds register_domain. This distinguishes it cleanly from siblings like get_contact, list_contacts, and update_registrant_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?

Explicitly routes the agent to list_contact_countries and list_contact_states before choosing country/state values, and names the downstream consumer (register_domain) plus reuse scope. That is when-to-use plus alternatives guidance, not mere implication.

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