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

Annotations already declare read-only, open-world, idempotent, so the bar is lower; the description still adds substantial operational context: a hard ceiling of at most five rows, an explicit statement that this is not complete history, a 15-minute cache window, and a precise request-cost model including that cache hits count and failures are free. That is exactly the behavior context annotations cannot carry.

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?

Four short sentences, purpose front-loaded, and each remaining sentence earns its place by disclosing a distinct constraint (row cap, cache TTL, cost model). No filler or restatement of the tool name.

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 two-parameter read tool with no output schema, the description covers purpose, data coverage limits, caching, cost, and a docs link. Return-value shape is only indirectly addressed via the fields enum, but nothing critical to calling it correctly is missing.

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 coverage is 100% and both parameters are self-documented, including the enum for 'fields', so the schema does the heavy lifting. The description adds only the notion of an 'exact' product ID, which is already stated in the q property description.

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 and resource (fetch recent individual sales) and constrains the scope to an 'exact product', which implicitly separates it from tcgplayer_search. An agent can tell immediately this returns sold-transaction rows for one known product ID rather than search results.

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 'exact product' framing and the warning that this is not a complete sales history, but no alternative sibling is named and no explicit when-to-use/when-not rule is given. Adequate but leaves routing to inference.

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