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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), so the bar is lower, and the description adds real substance beyond them: the exact price aggregates returned, the distinction between open promotions and club-only promotions, a 90-day history window, and the purpose of the `page` field for quoting. It does not cover failure behavior (e.g., product not sold anywhere) or response shape/pagination, keeping it short of a 5.

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?

One dense, front-loaded sentence that enumerates only output-relevant facts; no filler or restatement of the name. It is somewhat list-heavy and would read better split, but every clause carries information.

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 no output schema and no annotations describing returns, the description correctly carries the return-value burden by naming each aggregate and the `page` link. It is nearly sufficient, missing only edge-case behavior (product absent from all chains) and any note on chain/currency coverage limits.

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% for the single `code` parameter (barcode GTIN/EAN, 6-14 digits), so the schema fully documents it. The description only echoes 'by barcode' and adds nothing about format or fallback behavior, which is the expected baseline when the schema does the work.

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 verb+resource with scope: prices of a single product identified by barcode, across every chain that sells it. This implicitly separates it from basket- and city-level siblings (compare_basket_by_chain, cheapest_stores_in_city), but no sibling is named explicitly.

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?

Usage is implied rather than stated: the 'one product (by barcode)' framing signals this is the lookup to use once you already have a barcode (unlike search_products). There is no explicit when-to-use, when-not-to-use, or named alternative, so the agent must infer routing from the input shape.

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