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

The annotations already declare readOnly, idempotent, non-destructive behavior. The description adds useful behavioral detail: it aggregates totals per period into a single bucket and returns totals plus absolute and percentage deltas. No side effects or destructive actions are mentioned, and none contradict 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 compact and well structured: a one-sentence summary, a brief implementation note, a statement of the return shape, and two illustrative examples. There is no fluff or redundant repetition of schema information.

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 high schema coverage and the existence of an output schema, the description sufficiently complements the schema by clarifying that the tool compares two periods and returns aggregate deltas. It could mention output details or pagination behavior more explicitly, but those are largely covered by the schema and annotations, so it is reasonably complete.

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 already describes every parameter, including formats, enums, defaults, and special requirements such as esfera requiring a value metric. The description does not add significant extra parameter semantics beyond the schema-provided details, so a 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 purpose: comparing two periods side by side for the same modality. It identifies the underlying aggregate call, explains that it wraps it twice, and gives concrete typical questions, which makes the intended use unmistakable.

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 explains that this is a wrapper over compras_aggregate_contratacoes_por_periodo and provides typical use cases, so when to use it is fairly clear. It does not explicitly name alternative sibling tools or state a condition for choosing one over another, but the wrapper framing and examples convey the intended context.

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