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

readOnlyHint=true already tells the agent this is a safe read, so the description's main added value is the return format, notably that the 3y figure is an annualized 0-1 fraction. It does not disclose whether returns are split/dividend adjusted, how missing history is handled, or the response shape — gaps that matter for interpreting the numbers.

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 content is front-loaded into one dense sentence listing periods and output format, followed by a short usage cue. The trailing Japanese sentence largely restates the English, which is a small redundancy but may follow a bilingual convention.

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 no output schema, the description does the necessary work of specifying which periods come back and that the 3y value is a fraction rather than a percentage — an important disambiguation. Only the exact field naming and behavior with insufficient history remain unstated, which is minor for a one-parameter read tool.

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?

The single parameter has 100% schema description coverage, including the '7203' = Toyota example, so the schema carries the semantics. The description adds nothing about the symbol beyond what the schema already says; baseline 3 applies.

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 names the exact resource (a period-returns bundle) and enumerates the periods returned (1d/1w/1m/3m/6m/1y/YTD plus 3y annualized), so an agent knows precisely what it gets. It signals a 'lightweight' variant exists relative to heavier siblings but never names which sibling to prefer, so it falls short of full differentiation.

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?

'Use for quick performance comparisons' gives an implied when-to-use context, but there are no explicit alternatives (e.g., get_historical_prices or get_technicals) or when-not conditions. An agent must infer the boundary itself.

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