Cheapest offer

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

Annotations already cover read-only/idempotent/non-destructive, so the bar is lower, yet the description adds real behavior: it skips unreliable and out-of-stock offers, examines top `candidates` matches rather than the lowest card price, and discloses request cost ('1 + candidates requests'). It also flags a failure mode (mismatched product name) that no structured field captures.

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?

Short and front-loaded: purpose first, then the usage trigger, then mechanism and cost caveat. Every sentence carries information. Slightly fragmented by line breaks and the abrupt final cost sentence, but no filler.

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 6-parameter tool with no output schema, the description does the needed work: it explains what is returned (best offer per match plus the overall cheapest), the filtering policy, and the cost. It is close to complete; only alternative-tool routing and result-format details (e.g. fields per offer) are absent.

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 baseline is 3. The description's only added parameter meaning is the cost consequence of `candidates` ('Costs 1 + candidates requests'), which the schema already partially implies with 'one request each'. It adds little beyond the schema for city, condition, min_score, or installment_only.

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 and mechanism — 'Cheapest trustworthy offer for a product named in words: searches, then looks at every shop's offer.' The phrase 'named in words' implicitly distinguishes it from URL-based siblings like tb_product_url, and the two-stage 'searches, then looks at every offer' differentiates it from a plain search tool.

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?

'Use for "where is X cheapest"' gives an explicit trigger condition. It also warns to verify the matched product name. However, it never names alternatives (e.g. tb_best_value, tb_compare, tb_offers), so the agent must infer routing among several price-comparison siblings.

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