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

Annotations already declare readOnlyHint and openWorldHint, yet the description adds substantial context: pricing ($0.002 USD per successful call via x402 on Base/Solana/Arc), no charge on failure, 404 rather than charge for missing barcodes, community-data caveat, and ODbL licensing/attribution. This is exactly the extra behavioral signal the annotations do not cover.

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?

Front-loaded with the return payload, then source, caveat and cost, so the most selection-relevant content comes first. The long nutrient enumeration is slightly verbose, but each clause carries signal an agent would otherwise have to infer.

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?

An output schema exists, yet for a paid open-world lookup the description still supplies the critical operational facts: data source, error semantics (404 for unknown barcodes), data-quality caveat, licensing, and billing behavior including which failures are free. Nothing needed to invoke it correctly is 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%, so all three parameters (barcode, name, limit) are already documented and the baseline is 3. The description echoes the barcode formats and confirms the name lookup, but adds no syntax, bounds, or interaction rules beyond what the schema provides.

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 resource (packaged food) and precisely what it returns (name, brand, quantity, Nutri-Score, NOVA group, per-100g nutrients, allergens, labels, ingredients, image), plus the two lookup keys (barcode formats or name). This is fully distinguishable from generic sibling tools like package_search or producthunt.

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?

It explains the two input modes (by barcode or by name) but never states when to prefer one over the other or when not to use this tool versus any sibling. Usage is implied from the input examples rather than an explicit when/when-not rule.

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