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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral detail: returns r, p-value, and R², max 30 candidates per call, processes candidates one at a time, and restricts to verified autario indicators. It doesn't cover edge cases or rate limits, but adds meaningful value beyond 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 dense but every sentence earns its place: purpose, use case, output format, limit, alternative, and supported data sources. Key information is front-loaded in the first sentence, and the alternative guidance is immediately actionable.

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 tool with no output schema, the description compensates well by naming return fields (r, p-value, R²), setting a candidate cap, and enumerating supported source families. The only notable gap is the absent semantics for the optional time parameter, but overall an agent has enough to select and invoke this correctly.

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 coverage is 75%, so the baseline is 3. The description enhances the schema by clarifying that target_indicator is 'the KPI you want to explain' and candidates are 'candidate indicator IDs' with a hard max of 30. The time parameter is left undocumented in both schema and description, preventing a 5.

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 ('Rank'), a clear resource ('candidate drivers of a KPI'), and a distinctive methodology ('order them by correlation strength'). It differentiates itself from the sibling decompose_drivers by noting when overlap exists, so an agent can distinguish this from related tools without opening schemas.

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?

It explicitly says when to use it: for 'what moves my KPI?' questions, and provides a clear when-not with an alternative: 'Use decompose_drivers instead when the candidates may overlap.' This gives actionable routing guidance beyond generic context.

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