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

Annotations already declare read-only, idempotent, non-destructive, and closed-world behavior. The description adds useful context beyond them: daily granularity, per-printing output, USD currency, the 7–1000 day range, February 2024 history start (later for newer cards), and the no-forecast limitation.

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 tight sentences with zero waste. The usage trigger is front-loaded, followed by return granularity, then the past-only limitation.

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 an output schema, annotations covering safety, and 100% schema description coverage, the description still supplies the key behavioral context an agent needs: when to call it, what period it returns, and that it excludes forecasts.

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 the schema documents both parameters. The description adds the historical-start caveat and the 'later for newer cards' nuance that affect interpretation of `days`, though it repeats the 7–1000 range already in the schema and adds nothing extra for `product_id`.

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 (Returns) and resource (daily market price per printing), and scopes it to historical data with 'Past prices only, no forecasts.' This historical, past-only scope distinguishes it from current-price or all-time-high/low 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 enumerates triggering user questions: whether a price is going up or down, how it moved over a period, or what it was worth on a past date. It also gives an exclusion ('no forecasts'), but does not name sibling alternatives such as card_price or all_time_highs.

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