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

Annotations already carry the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false), and the description adds real value on top: the auth requirement, what happens without an account, and a hard rule against fabricating addresses. It does not warn that repeat calls create duplicate records despite idempotentHint=false.

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 tight sentences with the core action and field set front-loaded, followed by the sourcing rule and the auth caveat. No filler and no repetition of schema structure.

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 an output schema present, return values need no explanation, and the description covers auth, data provenance, field scope and the default option. It is nearly complete; duplicate-creation behavior and the boundary with update_address remain 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 coverage is only 45%, so the description compensates by naming nearly every field in the parenthetical, including format cues ('state code, four-digit postcode'). Minor gaps: address_line2 and the home/business meaning of 'type' are not explained.

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 opens with a specific verb plus resource ('Saves an Australian delivery address to the address book') and scopes it to 'the current buying context'. It enumerates the captured fields and notes the optional default flag, which distinguishes it from set_default_address and update_address in the sibling list.

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?

It gives a clear directive on sourcing data ('Collect it from the customer; never invent one') and states the signed-in-account prerequisite, including the fallback sign-in flow. It does not, however, say when to prefer update_address or set_default_address over this tool.

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