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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds real context beyond that: that checkout_url is an external link on shop.nevini.wine, that no order or payment occurs, and that the line_id returned feeds update_cart. It stops short of describing pagination or freshness of 'live' prices.

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 tightly written sentences, front-loaded with the return payload and then the non-side-effects and routing. No redundant or filler clauses.

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?

Output schema exists and annotations carry the safety profile, so the description only needs to clarify side effects and routing — both of which it does. An agent has everything needed to call it correctly and interpret checkout_url safely.

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%, with cart_id documented down to the ?key= suffix and language carrying an enum plus defaults in the schema. The description adds nothing about either parameter, so baseline 3 applies.

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 plus what is returned: 'Returns the current lines, live prices, subtotal and checkout_url of a cart.' It also separates itself from the mutation siblings by noting it changes nothing and by naming update_cart as the tool to use when a line_id is needed.

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 use cases ('show the cart again or to look up line_id for update_cart') and a boundary ('No order is placed and no payment is taken here'). It doesn't explicitly exclude create_cart or restate when a fresh cart is needed, but the routing guidance is clear.

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