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

Annotations already mark readOnlyHint and idempotentHint, and the description reinforces and extends this with non-obvious behavior: it 'opens nothing, holds nothing, and no money moves,' the token is bound to the priced address, and an escrow hold cannot be topped up later. There is no contradiction with 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?

The description is longer than average but every sentence carries a critical constraint or next step, and the purpose is front-loaded. The length is justified by the domain complexity: token binding, escrow behavior, and checkout sequencing all need explanation.

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 no output schema, the description covers the essential return information (carrier services, prices, `rate_token`), the lifecycle of the token, the prerequisite relationship to checkout_intent, and the digital-order exception. An agent has enough to call the tool correctly and know what to do with the result.

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 100%, so the baseline is 3, but the description adds important semantic meaning: the same `items` and `ship_to` must be reused at checkout, the `buyer_email` must be the real one, and the address the token is bound to must not be retyped. This goes beyond the schema's field descriptions.

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 'What it costs to ship an order, and the token that lets you buy it' and then defines its output as carrier services with prices and a `rate_token`. It is clearly distinguished from siblings like checkout_intent, which consumes the token, and booking_intent.

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 description explicitly states when it is required: 'REQUIRED before checkout_intent on anything physical', and when it is not needed: 'A digital-only order needs none of this.' It also gives the exact follow-up: pick a service and pass its token to checkout_intent, with the same `items` and `ship_to`.

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