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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description earns credit by disclosing how the estimate is derived: Deer's product-page quotes, a noon Eastern same-day ship cutoff, and fastest-service shipping for pens. It does not address error handling for invalid postal codes, but that is minor given the annotation coverage.

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 states the purpose first and then the computation rules. Dense but every clause (Canadian postal code, noon Eastern cutoff, pen service) carries information; no filler or repetition.

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?

For a simple read-only estimate with no output schema, the description supplies the basis of the calculation and the meaning of both inputs, which is enough for correct invocation. It could say more about the shape of the returned dates, but the 'ship and arrive' phrasing covers the essentials.

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 50%: includes_pens is documented in the schema, but postal_code is not. The description partially compensates by specifying the postal code must be Canadian and by explaining the pen-shipping behavior that maps to includes_pens ('pens travel on the fastest service'). It adds meaningful constraint beyond the schema but does not fully cover the undocumented parameter's format.

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 names a specific computation (ship and arrival dates for an order placed now) and the resource (a Canadian postal code), making it clearly distinct from track_order (existing orders) and get_store_info. It stops short of explicitly naming a sibling to route against, but the hypothetical-new-order framing makes the purpose unambiguous.

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?

It clarifies the scenario (an order placed now) and the input domain (Canadian postal code), which implies when to reach for it. However, there is no explicit when-to-use/when-not guidance or named alternative (e.g., 'for an order you already placed, use track_order instead'), leaving the boundary to inference.

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