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

Annotations indicate readOnlyHint=true, so the description aligns with read-only behavior. It adds value by disclosing that the estimate uses placeholder contact details and is not the final rate, which is a meaningful behavioral caveat beyond the annotations. It doesn't mention rate limits or further data, but the read-only nature is well covered.

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 two sentences long, front-loaded with the primary function, and includes a crucial caveat about placeholder details. No waste; every sentence earns its place.

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 moderate complexity (5 parameters, all documented, read-only, no output schema), the description is sufficient. It tells the agent what the tool does and the key limitation (placeholder rates), which is the main contextual gap. It doesn't need to explain return values since no output schema is expected, and the safety is clear from annotations.

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. The description does not add extra meaning to parameters beyond what the schema provides, but it reinforces the context that the estimate depends on the destination and items. No parameter is undocumented, so the schema carries the weight.

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 clearly states the verb 'estimate' and the resource 'delivery services, charges, and transit times' for a basket to a destination. It distinguishes itself from siblings like check_shipping_availability and check_express_eligibility by focusing on estimation with placeholder details, which is a unique purpose.

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 implies when to use: when an estimate is needed before checkout, and notes that exact rates are confirmed at checkout. It doesn't explicitly name sibling alternatives like check_shipping_availability, but the context is clear enough for an agent to infer.

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