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

Annotations already declare read-only, idempotent, open-world, non-destructive operation. The description adds critical behavior beyond annotations: it is a stub that returns no sold prices, requires an Attic API key, and does not offer PCGS comps, preventing an agent from misusing it. It also warns against inventing data.

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, front-loaded with 'STUB.' so the critical caveat is seen immediately. Each sentence adds a distinct warning or requirement: no sold prices, no pricing use, no fabrication, API key, no PCGS comps. No wasted prose.

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 four-parameter, read-only stub with full schema descriptions and rich annotations, the description supplies the essential caveats: non-functional, no sold prices, auth requirement, and PCGS exclusion. It could go further by naming an alternative tool, but the core completeness is high.

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 every parameter has a description, so the schema already carries parameter meaning. The description adds no syntax, format, or constraint details for q, days, limit, or category beyond what the schema states. Baseline 3 is appropriate.

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 it is a STUB and explicitly says it does not return sold prices for coins, clarifying the resource and its negative capability. The name 'sold comps' would otherwise mislead, and the description corrects that. It does not explicitly name a sibling alternative, but the stub framing makes its purpose unambiguous.

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?

Says 'Do not call this to price a coin' and 'do not invent a hammer,' providing a clear when-not-to-use warning plus an anti-hallucination instruction. It also notes an API key requirement. However, it names no alternative tool and gives no positive condition for calling this stub, leaving routing to inference.

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