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

Annotations already indicate read-only/idempotent safety, but the description adds substantial context: the index is chain-linked base 100, includes 7/30/90-day movement, total market value, median price, and product count. It also discloses cross-market behavior and the comparison cap of 3 scopes, enriching 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?

Three sentences, front-loaded with purpose, and each sentence earns its place: definition and metrics, usage examples, and exclusion/alternative guidance. No waste or redundancy.

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 read-only trend tool with no output schema, the description is complete: it explains what data is returned (index, movement, totals, median, count), when to use it, and how to compare scopes. All necessary context is present without needing to infer behavior.

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%, so parameters are well-documented. The description reinforces scope semantics ('whole game or a single set') and the `vs` list format (comma-separated, up to 3 total), but does not add major new meaning beyond the schema. 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 clearly states it 'Shows the cross-market price trend for a whole game or a single set' with specific metrics, distinguishing it from single-card price tools via 'NOT a single card's price — use price_card or list_printings for one card.' This makes the tool's purpose unambiguous and differentiates it from siblings.

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?

Explicitly says to use it for '"how is Pokemon / this set trending" questions' and explains how to compare scopes with a `vs` list. It also gives exclusionary guidance: 'NOT a single card's price' and names alternative tools. This is excellent when/when-not guidance.

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