Compare prices

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

Annotations already indicate read-only, idempotent, non-destructive behavior. The description adds valuable context: the need for a Pro API key and the caveat that prices may be promotional or invalid, requiring verification. This goes beyond the annotations and informs the agent about data reliability.

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?

Two sentences, front-loaded with the core function, followed by necessary caveats. Every word earns its place; no redundancy.

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 tool, the description covers purpose, authentication, and a key usage caution. It implies the return includes pricing, promotion status, and validity. Without an output schema, this is reasonably complete, though it could mention return format or scope of retailers.

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?

The schema only provides a pattern for the 'ean' parameter without description (0% coverage). The description clarifies that the parameter is an EAN and that the tool compares it across retailers, giving semantic meaning to the parameter. With a single parameter, this is sufficient compensation.

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 clearly states the tool's function: 'Compare an EAN across retailers.' It uses a specific verb and resource, and this distinguishes it from sibling tools like get_price_history or match_by_ean, which focus on single-retailer history or matching.

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 explicitly states a prerequisite (Pro API key) and provides a usage directive: 'inspect promotion status and validity before presenting a current cheapest price.' This gives clear context on when and how to use the result, though it does not mention alternatives by name.

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