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

Annotations already declare readOnly, openWorld and idempotent, so the safety profile is covered. The description adds genuinely new context: the rates are 'live' (an external, real-time dependency) and match what checkout will charge, which tells the agent results are authoritative and consistent rather than cached or approximate.

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?

A single front-loaded sentence that says what it returns, for what input, and why the numbers are trustworthy. The phrasing 'for the items to a destination' is slightly clumsy, but nothing is wasted.

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?

Return-format details are unnecessary because an output schema exists, and the input contract is fully documented in the schema. The description covers the remaining gaps an agent needs: this is a live external call and the rates coincide with checkout.

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%, and the nested address schema already spells out the country/postal-code/state requirements, so the schema does the heavy lifting. The description's restatement that state is needed 'in the US and Canada' adds little beyond what the schema says, which lands at the baseline.

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 gives a specific verb and resource ('Live FedEx shipping options and prices') and scopes it to items plus a destination. It is clear on its own but never names or distinguishes itself from siblings like check_price_and_stock or request_quote, so an agent must infer the boundary.

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?

'the same rates checkout charges' implies this is the pre-checkout rate check, which hints at when to use it. However, there is no explicit when-not guidance and no named alternative, leaving the agent to reason out whether check_price_and_stock or request_quote is the right call instead.

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