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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds that it returns the product's best offer for the given country, which is useful. However, it does not disclose behavior for not-found cases or per-language differences, leaving some gaps beyond 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?

The description is three sentences: first states the main action, second provides usage guidance, third summarizes the result. Every sentence earns its place with no redundancy or fluff.

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?

The tool is simple and has an output schema and good annotations, so the description need not cover return values. Core usage is explained well, but the language parameter is entirely omitted and edge behaviors (e.g. no match) are not mentioned, making it not fully complete.

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 67% (id and country described). The description enhances id by specifying GTIN/EAN/UPC barcode and Ponito product id, and frames country as determining country-specific offers. However, the language parameter has no schema description and is not mentioned in the description, leaving that parameter under-specified.

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 clearly states the tool 'looks up one product' by specific identifiers (GTIN/barcode or Ponito product id), making the verb and resource explicit. It also distinguishes this from sibling search_products by noting it is for when you already know exactly which product you mean.

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?

The description gives clear context for when to use the tool ('when you already know exactly which product you mean') with practical examples. It does not explicitly name alternatives or exclusion criteria, but the 'use this when' phrasing implicitly contrasts with search behavior, so it is clear.

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