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

Annotations already declare readOnly, idempotent, openWorld and non-destructive behavior, so the safety profile is covered. The description adds genuinely new context by disclosing that each call consumes one lookup from a monthly allowance even on a miss — a real cost trait not present in the annotations. It does not say what is returned on a not-found code, leaving the failure behavior ambiguous.

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?

Three short sentences, front-loaded with the core action, with no filler. The return-field list is dense but earns its place given there is no output schema.

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 single-parameter lookup with no output schema, the description covers inputs, probable return fields, and quota cost, which is close to sufficient. The remaining gap is the not-found outcome — it mentions a lookup is consumed on a miss but not whether the result is an empty payload or an error.

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% and the schema already documents the single parameter, its example, and that spaces and dashes are ignored, so the baseline of 3 applies. The format enumeration (UPC-A through ISBN-13) adds some meaning about acceptable inputs, but it does not add notation or normalization rules beyond the schema.

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 gives a specific verb and resource ('Find the product for one barcode') and enumerates the accepted symbologies, so an agent knows exactly what it retrieves. The phrase 'one barcode' implicitly contrasts with the plural sibling lookup_barcodes, but no sibling is named, so differentiation is left to inference.

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 only implied: a single known barcode goes here. There is no explicit guidance on when to prefer lookup_barcodes (batch) or search_products (e.g. when the barcode is unknown or a miss occurs), and no fallback path is suggested after a not-found result.

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