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

Annotations already establish this as a safe, idempotent, non-destructive read, so the bar is lower. The description adds genuinely new behavioral content: how offers are matched into the same product set, that the result is ordered by cheapest total price, and that each entry carries a delivery promise. It omits result limits/pagination.

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?

Three tight sentences: what it returns, why you'd call it, and which argument to supply. The core behavior is front-loaded and no sentence is filler.

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 annotations covering the safety profile and no output schema, the description does the heavy lifting well by describing the returned list, its ordering, and the delivery information. One gap remains: zero parameters are marked required, yet the description only says to pass one of the two identifiers, leaving the behavior when neither is supplied unspecified.

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 the baseline is 3. The description goes slightly beyond the schema by framing product_key and offer_id as interchangeable ways to address the same product and by explaining the matching basis (barcode or brand + part number) that underlies the key.

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 concrete verb and resource ('list every shop selling the same item'), plus the matching rule (barcode or brand + part number) and the ordering (cheapest total price first). The 'for one product' scoping implicitly separates it from compare_products (multi-product) and search_products, so an agent can route correctly.

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 gives clear context via the two questions it answers ('where is this cheapest', 'who delivers it tomorrow') and guidance on which identifier to pass ('Pass product_key or offer_id'). It stops short of naming alternatives or stating when not to use it, so no explicit exclusion guidance.

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