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

Annotations already declare this a safe read-only, idempotent, closed-world operation, so the bar is lower. The description still adds real context: the result is personalized to the signed-in user, ranked by cost-effectiveness, and includes copies to buy, cost, and which decks are advanced. It does not mention auth requirements explicitly beyond 'signed-in user' or any rate limits.

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?

Purpose is front-loaded in the first clause, and the second sentence is a legitimate clarification of return fields. The first sentence is dense and em-dash-heavy but contains 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?

With no output schema, the description carries the return-value burden and does so by naming the fields returned (copies, cost, decks advanced) and defining fromPct/toPct. What is missing is input-side detail for limit/format/source, but the core read-only recommendation behavior is adequately framed.

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 67% (format and source documented; limit has only min/max/default). The description explains none of the three actual inputs and instead defines fromPct/toPct, which are not parameters — an agent could wrongly hunt for them in the input. With one genuinely undocumented parameter and no compensating input guidance, this is below the 3 baseline.

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 verb (buy) and resource (single cards) plus a clear ranking criterion: cards that move the signed-in user closest to completing current tournament decks per money spent. The 'per money spent' framing implicitly separates it from market_movers and price_list, but no sibling is named, so it falls short of explicit differentiation.

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 scope ('current tournament decks', 'given what they already own') implies when this applies, but there is no explicit when-to-use, no when-not, and no named alternative among the 17 siblings. Usage must be inferred from the purpose sentence.

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