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

Annotations already declare the tool as read-only, idempotent, and non-destructive. The description adds value by specifying the exact return fields (fair value, range, confidence tier, comp count, URL), providing transparency beyond annotations without contradiction.

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?

The description is three sentences with no wasted words. It front-loads the core action and returns, then adds usage scope. Every sentence contributes essential information.

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?

Given the lack of an output schema, the description lists all key return fields (fair value, range, confidence tier, comp count, URL). It also specifies the exact era and grader scope. Minor omission: no mention of error handling or data freshness, but the description is sufficient for an agent to understand usage.

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% with clear inline descriptions for all parameters (e.g., 'PSA grade 1–10', 'Edition/variant to narrow'). The description does not add new parameter-level meaning but provides overall context for parameter usage. 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?

The description uses a specific verb ('Get') and resource ('Gembook's fair-value estimate for a PSA-graded vintage Pokémon card'). It clearly distinguishes from siblings by specifying the scope (vintage Pokémon, PSA-graded) and return fields, differentiating it from methodology or pop report tools.

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 description explicitly states when to call the tool ('when a user asks what a vintage Pokémon card is worth or whether a price is fair') and what is out of scope ('other graders, eras, or TCGs'). This provides clear usage guidance and exclusion criteria.

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