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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive. The description adds crucial context beyond annotations: it clarifies the call 'opens nothing, holds nothing, and no money moves' and explains the token-binding behavior ('retype the address and it stops matching'). This exceeds what annotations convey, giving the agent a complete safety and state model.

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 somewhat long but every sentence carries weight: purpose, requirement, flow, token binding, safety, and exclusion. It is front-loaded with the core purpose and ends with the digital-only caveat. The density is justified by the tool's complexity, though it could be trimmed slightly without loss.

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?

Given the nested parameters and no output schema, the description adequately explains the return content (carrier services with price and rate_token), the token's binding, and the absence of side effects. An agent has all necessary information to call the tool correctly and understand the result. No critical gaps remain.

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 parameters are already documented. The description reinforces the semantic connection between parameters ('Pass the same `items` and the same `ship_to` you will check out with') and explains the rate_token's lifecycle, which is not in the schema. This adds meaning beyond the schema, though the baseline was already 3.

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 states a precise verb and resource ('what it costs to ship an order, and the token that lets you buy it') and clearly distinguishes from siblings by naming checkout_intent and explicitly excluding digital-only orders. An agent can immediately understand the tool's role in the checkout flow.

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 gives explicit when-to-use ('REQUIRED before checkout_intent on anything physical'), when-not-to-use ('A digital-only order needs none of this'), and the exact invocation sequence (pass same items/ship_to, receive rate_token, pass token to checkout_intent). It also warns about the address-binding caveat, leaving no ambiguity about prerequisites or alternatives.

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