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

Beyond the read-only annotation, the description adds rich behavioral details: deterministic computation, specific period comparison, handling of one-offs, cents units, and behavior for optional month. This goes well beyond what annotations convey, giving the agent a thorough understanding of the tool's behavior.

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 long but every sentence adds value, covering purpose, methodology, return fields, and parameter semantics. It is front-loaded with the core purpose and structured logically, making it easy to process despite its length.

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?

With no output schema, the description thoroughly explains all return components, units, and the behavior of the optional month parameter. It is complete for a tool of this complexity, covering all necessary context for an agent to invoke it 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 100% for the single optional parameter, but the description adds meaningful behavior beyond the schema: it explains that for a completed past month, the whole month is compared, and for the current month it uses month-to-date. This enriches the parameter's meaning.

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 it is a diagnostic breakdown of why net profit moved, using specific verbs and a defined resource. It also distinguishes itself from sibling tools by emphasizing the deterministic comparison logic and the focus on profit drivers, which is unique among the listed siblings.

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 provides clear context for when to use the tool, explaining the comparison methodology and return values. However, it does not explicitly mention when not to use it or point to alternative tools (e.g., income_statement), so the guidance is strong but not fully explicit.

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