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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states the calculation but does not indicate whether the risk-free rate is configurable, how the price series should be formatted (comma-separated, JSON array, etc.), or what the return value represents. For a pure computation tool, this leaves significant behavioral gaps despite the operation being conceptually simple.

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 a single, efficient sentence: 'Sharpe: Calculate the Sharpe ratio of returns. Provide a values price series; measures risk-adjusted return.' It front-loads the core action and includes only what is needed. No filler 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?

With no annotations, no output schema, and only one parameter, the description should at least clarify input format and what the output represents. It mentions 'price series' and 'risk-adjusted return' but omits formatting details and does not explain assumptions (e.g., constant risk-free rate). This is insufficient for an agent to invoke the tool confidently without additional guessing.

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 description coverage is 100%, so the schema already documents the single 'values' parameter. The description adds only 'Provide a values price series,' which does not clarify the expected format (e.g., comma-separated numbers, JSON array) or units beyond what the schema provides. Baseline 3 is appropriate when the schema does the heavy lifting.

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 states a specific verb and resource — 'Calculate the Sharpe ratio of returns' — which is clear and distinct from siblings like x402-sharpe-ratio (though that sibling exists, the definition doesn't differentiate itself from it) and other finance tools like x402-sortino or x402-max-drawdown. It does not, however, name a sibling or explain how it differs from the similarly-named x402-sharpe-ratio tool, so it falls short of a 5.

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 implies usage by specifying 'Provide a values price series' and stating what the tool measures ('risk-adjusted return'), but it offers no explicit when-to-use or when-not-to-use guidance relative to alternatives like x402-sharpe-ratio or other risk metrics. The implied context is adequate but leaves the agent to infer the appropriate scenario.

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