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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description usefully adds the hard limit of three products and the fact that units may be mixed, but it says nothing about what the response contains or how per-unit values are normalized.

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?

Three short sentences with no filler, and the example anchors the abstract idea of a unit price. Minor deduction: the illustrative example is placed before the actual purpose statement, and the trailing URL adds no task value.

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?

Ten parameters, no output schema, so the description carries some burden for return values; it never says the tool returns per-unit prices and which product is cheapest, only that it 'finds' the lowest price. Inputs are adequately framed, but the output contract is left implicit.

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 p1-p3, q1-q3, u1-u3 and currency are all documented in the schema itself; baseline is 3. The description adds 'mixed units' and 'up to three sizes,' which conceptually ties the p/q/u triplets together, but it adds no format or semantics beyond that.

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 second sentence states the operation concretely: compare up to three package sizes in mixed units to find the lowest unit price. That distinguishes it from generic converters like unit_converter or currency_converter, though it never names a sibling, so differentiation is inferential rather than explicit.

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 by the worked example (comparing a 500 g pack to a 1 kg pack) and by 'compare up to three sizes ... to find the lowest price,' which tells the agent the comparison scenario. There is no statement of when NOT to use it or what alternative to pick for single-price conversions.

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