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

Annotations already establish a safe, idempotent, closed-world read, and the description adds substantial context beyond them: the fixed 30-ETF universe, the correlations are backward-looking weekly returns over up to three years, the 1-6 holding cap, the specific derived figures returned (down-week correlation, volatility with 10% weighting, weight overlap), and the mandatory not-investment-advice note on every answer.

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?

Front-loads the trigger conditions and the exclusion list, which is the right ordering. It is dense but mostly earns its length, though the nested clause describing the correlation groups ('the three groups whose lowest is lowest') is convoluted and the return-value detail partly duplicates the output schema.

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 single-parameter, read-only analytical tool with full annotation coverage and an output schema, the description supplies everything an agent needs: trigger, universe, methodology, holding limit, disclaimer, and explicit sibling routing. No material gap remains.

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 nested position object, the all-or-none amount rule and ticker casing are already documented in the schema. The description only restates the 1-to-6 holding limit, adding no format or unit detail beyond what the structured field already provides.

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 capability (ranking ETFs by diversification benefit for a held portfolio), the mechanism (correlation of weekly returns on a fixed 30-ETF list across six exposure groups), and the output shape. It explicitly distinguishes itself from compare_etfs, get_etf_overlap_matrix and get_etf_portfolio_risk by naming them as the wrong tools for adjacent questions.

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?

Opens with the exact user phrasings that select this tool ('which ETFs would diversify', 'what could be added', 'which moved least with what they hold') and closes with an explicit 'Not for...' clause naming three sibling alternatives and the question each actually answers. Nothing is left to inference.

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