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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful behavioral context beyond them: the upstream data source (Open Food Facts), the packaged-food scope limit, and the per-call paid cost ($0.002 USDC via x402), which is exactly the kind of thing an agent must budget for.

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 dense sentence, front-loaded with the verb and resource, then the return payload, then cost. It is long but every clause carries information; only the enumeration of Nutri-Score/NOVA/eco-score is arguably padded.

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 no output schema, the description correctly enumerates the return contents (name, brand, ingredients, allergens, scores, per-100g nutrition) and discloses cost and source. Missing only failure behavior for unknown or non-food barcodes, which is minor for a one-parameter 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?

Only one parameter and schema coverage is 100%, with the schema itself documenting 'EAN or UPC digits'. The description restates the same input form without adding format, checksum, or length guidance, so the baseline of 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?

States a specific verb+resource ('Product barcode lookup') and names the data source (Open Food Facts) plus the returned fields, so the agent knows exactly what it gets back. It does not differentiate itself from the sibling barcode_read, which is a real ambiguity given the near-identical name.

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 implied rather than stated: the 'packaged food from its EAN/UPC barcode' scoping tells the agent this is for food products with a numeric barcode, but there is no explicit when-to-use, when-not-to-use, or named alternative to barcode_read/nutrition for non-food barcodes.

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