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

Goes well beyond the annotations: it discloses that the offer is re-checked at the requested quantity, that the return is a checkout_url, that nothing is charged until the order is placed, and that a concierge offer follows a different path returning the product page and creating a pending hold during shop hours. That is real behavioral context an agent could not derive from the schema.

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?

Front-loads the trigger and the required identifiers, then the outcome, then the concierge exception. It is dense and slightly run-on in the second sentence, but nearly every clause carries information an agent needs.

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?

Covers the trigger, all required inputs, the outcome (checkout_url and the pending-hold exception) and the no-charge-until-placement guarantee. With an output schema present, return-value documentation is not owed, so nothing material is missing.

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%, so each parameter is already documented, and the description largely restates those same constraints (exact variant product_id, eligible store_id). The only added nuance is that quantity is re-validated against the offer, which is marginal. Baseline 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?

States a specific action (starting a checkout for a chosen purchase) and enumerates exactly what inputs identify the item and offer. It implicitly separates itself from complete_checkout by noting 'nothing is charged until they place the order', but never names that sibling, so the differentiation is left to inference.

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 a clear trigger condition ('Call when the shopper has chosen to buy') plus preconditions on product_id (exact variant) and store_id (offer with is_eligible_checkout true). It stops short of naming alternatives or an explicit when-not-to-use case, e.g. what to do if the offer is not eligible.

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