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

Annotations already establish that this is a safe read-only operation. The description adds meaningful behavioral detail beyond the annotations: the exact metrics compared and the implicit comparison-with-preceding-period behavior when period_b is omitted.

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?

Two tightly written sentences. The core comparison behavior is front-loaded, and the fallback condition follows naturally with no wasted words.

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 read-only reporting tool with complete schema coverage and no output schema, the description provides enough context: it identifies the comparison dimensions and the default behavior. It could be slightly more complete by clarifying return shape or how this differs from other reporting tools.

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 100%, so the schema already documents all three parameters thoroughly, including formats and defaults. The description reinforces the period_b default, but adds little parameter semantics beyond what the schema 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?

The description states a specific verb and resource: compares two periods side by side and names the metrics compared. It is clear what the tool does, but it does not explicitly distinguish itself from related siblings like get_sales_summary or multi_store_report.

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 explains the fallback behavior when period_b is empty, which is useful contextual guidance. However, it gives no explicit guidance on when to use this tool instead of alternatives such as get_sales_summary or sales_forecast.

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