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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, but the description adds meaningful behavior: it computes an optimal split, accounts for shipping costs and free-shipping thresholds, and returns the lowest total including shipping. It also surfaces the dependency on prior get_best_price calls, which is useful operational context beyond the annotations. No contradiction 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?

The description is three sentences, front-loaded with the core purpose and followed by a short prerequisite. The only mild redundancy is 'Takes an array of EAN barcodes,' which is already in the schema, but it is brief and does not obscure the useful content.

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?

The output schema covers return values, the input schema covers parameters and constraints, and the description covers purpose, algorithm, and prerequisite workflow. For an optimizer tool with a documented output schema, nothing essential 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%, with both eans and country fully documented including format, pattern, default, and enum values. The description only restates that the tool takes an array of EAN barcodes, adding little beyond the schema, though it does imply these should come from prior get_best_price lookups.

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 opens with a specific verb and resource ('Find the cheapest way to buy multiple products together') and explains the exact computation: the optimal split across shops, including shipping costs and free-shipping thresholds. This clearly distinguishes optimize_cart from sibling tools like get_best_price, which handles individual products.

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 explicit workflow guidance: 'For accurate results, call get_best_price for each EAN first, then call optimize_cart.' This tells an agent when in a sequence to use the tool, but it does not explicitly state when not to use it or name alternative cart-level approaches.

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