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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is covered. The description adds that aggregation widens from brand to whole fleet depending on the argument, but does not discuss cost, result size, or freshness — modest added value on top of structured data.

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?

Three tight sentences, front-loaded with the core action and scope, followed by return shape and use case. No filler; a small amount of redundancy with the schema on the `brand` conditional keeps it from a 5.

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?

An output schema exists, so the return values need not be enumerated in detail, and the description still signals the statistic set and the reference to `model_summary` for metric definitions. Complete enough to invoke correctly, with the only gap being which concrete metrics are included.

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%, and the schema already explains that `brand` is an optional lowercase identifier restricting aggregation. The description restates the same conditional behavior, so it adds no meaning beyond the schema — the baseline 3 applies.

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 verb (aggregate) and resource (battery metrics) with explicit scope: entire fleet, or one brand when `brand` is set. It distinguishes itself from sibling `model_summary` by mapping its return shape to that tool's metrics and framing the output as a baseline for comparison.

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?

Explicitly states the use case: 'fleet-wide baselines that a single device or model can be compared against,' which tells the agent when this tool is the right pick over device- or model-level summaries. It stops short of explicitly naming the alternative tools or stating when NOT to use it.

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