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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, covering safety. The description adds valuable behavioral detail: the Euler decomposition summing to 100, the diversification ratio, and the specific matrices returned. It also specifies the time window (up to three years of weekly returns), which is not in annotations.

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, well-structured sentence that front-loads the primary purpose and lists all key outputs without any filler. Every element contributes to the agent's understanding.

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?

The description lists all major outputs (volatility, risk shares, diversification ratio, matrices) and the time frame. While there is no output schema, the description sufficiently conveys what the tool returns. It could mention edge cases or limitations, but the schema covers constraints like maxItems and optional amounts.

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 input schema has 100% coverage, with detailed descriptions for both parameters (currency and positions). The description adds no additional parameter semantics beyond what the schema already states, so the baseline score of 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 the tool's function: it computes portfolio volatility, risk decomposition via Euler, diversification ratio, and correlation/covariance matrices for a list of US ETFs. It is specific enough to distinguish it from sibling tools like overlap_matrix or compare_funds, which serve different analytical purposes.

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 the tool is for analyzing risk contributions in a portfolio of US ETFs. It provides clear context (portfolio of US ETFs, weekly returns over up to three years) but does not explicitly mention when not to use it or name alternatives. This fits the 'clear context, no exclusions' level.

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