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

With no annotations, the description carries the full burden. 'Look up' weakly implies a safe read, but it says nothing about what happens when the EAN isn't found, whether an error or empty result is returned, or what the response shape looks like (no output schema either).

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 front-loaded sentence with zero filler; the resource and the lookup key come before anything else. Nothing in it is redundant.

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 simple single-parameter lookup with full schema coverage, the description covers the core purpose, but with no annotations and no output schema it leaves the not-found / error behavior entirely unspecified. That is the one thing an agent most needs for an exact-key lookup.

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 100% — the schema already gives the EAN-13 pattern and an example. The description names the parameter domain ('EAN barcode') but adds no format or handling detail beyond what the schema states, so 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?

Specific verb ('look up') plus resource ('product in the ShelfAtlas catalog') plus key ('by its EAN barcode'), so the agent knows exactly what this does. It doesn't distinguish itself from siblings like search_products or search_catalog_offers, which an agent could easily confuse with an exact-EAN lookup.

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 'by its EAN barcode' phrasing implicitly frames this as an exact-identifier lookup, which a careful agent can contrast with its search-shaped siblings. However, no explicit when-to-use or when-not-to-use guidance is given, and no alternative is named.

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