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

Annotations already mark readOnlyHint and idempotentHint true. The description adds context beyond this: it explicitly states 'Read-only, area-level aggregates only, no personal data' and explains how to interpret coefficients near +1/-1. This is useful behavioral transparency without contradicting the 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 three sentences: the first states the core purpose, the second explains the methodology and the added note, and the third covers interpretation and privacy. Every sentence earns its place and it is front-loaded with the key action.

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?

Given the tool's simplicity (one parameter, output schema present), the description is complete: it covers methodology, output content (strongest relationship note), interpretation guidance, and privacy. It does not explicitly tie the 'level' parameter to the areas being correlated, but that is already in the schema, so the description adequately complements the structured data.

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 provides 100% coverage for the single 'level' parameter, including allowed values and a default. The description does not add parameter-specific meaning beyond what the schema already states, so the baseline 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 starts with 'Return pairwise correlations between the six indicators across areas,' using a specific verb and naming the exact resource. This clearly distinguishes it from siblings like indicator_ranking and score_trends, which focus on rankings and trends rather than pairwise relationships.

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 relationships between indicators across areas and notes it works on area-level aggregates. It gives clear context for when to use it, but does not explicitly mention alternatives or when not to use it, so it falls just short of a 5.

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