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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds real value by disclosing the returned payload (per-store stock, category path, card link), which matters since there is no output schema. It does not mention behavior when neither key is supplied.

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?

Two tightly packed sentences: the first front-loads what data is returned, the second states the two lookup keys. No filler or redundant restatement of the name.

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 read-only lookup with no output schema, the description compensates by enumerating the return contents and both lookup paths. The only gap is that both parameters are optional with no statement of precedence or behavior when neither is given.

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 both parameters (product_id provenance, EAN-8/EAN-13 barcode with significant leading zeros) are already documented in the schema. The description only restates these at a higher level, adding no syntax or format detail beyond the structured fields. Baseline 3 applies.

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 (retrieve full info about a specific product) and enumerates the returned fields: price, barcode, SKU, brand, category path, card link, per-store stock. It also names the sibling search_products as the origin of product_id, letting an agent distinguish lookup from search without opening either schema.

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 clear context: look up by product_id obtained from search_products, or by EAN barcode. The barcode path is presented as an alternative input, which is implicit routing guidance, but no explicit when-not-to-use or exclusion is stated.

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