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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds meaningful behavioral detail: results cover every shop that carries the product, are sorted cheapest-first, and include stock status and purchase links. No contradiction with the annotations exists.

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?

A single sentence front-loads the core action ('Look up a single product by its EAN barcode') and then packs the output details into a compact list: price at every shop, cheapest-first, stock status, and purchase links. Every phrase earns its place and there is no 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 an output schema present and annotations covering read-only/idempotent behavior, the description supplies exactly the remaining selection-level context: single-product EAN lookup, cross-shop price comparison, ordering, stock, and links. Nothing an agent needs to choose or invoke this tool correctly appears to be 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%: ean has a pattern and example, country has an enum and default, and reference_shop is explained. The description adds no extra parameter meaning beyond saying 'by its EAN barcode,' but it doesn't need to because the schema fully handles semantics. Baseline 3 is appropriate.

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 uses a specific verb ('Look up') and resource ('single product by its EAN barcode'), and it names the exact output: price at every shop, sorted cheapest-first, with stock status and direct purchase links. This clearly distinguishes it from siblings like search_product or find_alternatives_for_product. The 'single product' qualifier removes ambiguity about scope.

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: use this when you have one EAN barcode and need prices across shops. The word 'single' and the focus on price comparison imply when this tool is appropriate. It stops short of explicitly naming alternatives or stating when not to use it, but the context is unambiguous enough.

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