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

Annotations already declare the tool read-only, idempotent, and non-destructive. The description adds useful behavioral context: prices are VAT-excluded, in EUR, converted using current exchange rates, and represent 'known' data with a potential completeness limitation. It does not cover edge cases or data freshness, but it goes beyond the annotations.

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 two dense sentences with no filler. It front-loads the core output semantics and then gives a concrete use-case question, making every clause valuable.

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?

Given the output schema and rich annotations, the description adequately explains the return semantics. However, it leaves a significant gap around the required 'slug' parameter and how 'days' affects the result, so an agent may not know exactly how to invoke the tool correctly.

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 0%, and the description does not define either parameter. 'slug' is never mentioned, and 'days' is only weakly implied by the word 'Daily'. The description fails to compensate for the schema's lack of parameter documentation.

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 precisely defines the tool's purpose: it returns daily lowest VAT-excluded EUR prices, derived min/max/current values, and whether the price is at its lowest ever. The phrase 'Answers "has this ever been cheaper than X?"' reinforces the intended use. It does not explicitly contrast with sibling tools like compare_prices, but the content is specific enough to distinguish it.

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 sentence 'Answers "has this ever been cheaper than X?"' provides a concrete trigger condition for when to use the tool. It gives clear usage context, though it does not mention exclusions or point to alternatives such as compare_prices.

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