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

Annotations already declare readOnly/openWorld/non-destructive, yet the description adds real behavioral context: the required Cotlet API key scoped to this app, the one-period-per-call invariant, that results come 'as Zen Planner reports it,' and that the total is the aggregate of groups. These matter because there is no output schema to reveal the shape.

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 report scope and grouping are front-loaded and the sentences are short. There is mild redundancy, since the first and second sentences both say revenue is returned for a date range grouped as chosen, which slightly dilutes the efficiency.

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 carries more of the return-value burden and does so reasonably: period, grouping, and the aggregate semantics (total = sum of groups). It stops short of describing the per-group fields or units, but covers what an agent needs to call and interpret 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%, so from/to and the group_by enum are already fully documented. The description restates the group_by values ('membership type, class, instructor, location or retail') without adding format or semantic detail beyond the schema, so 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 and resource ('Revenue for a period') plus the grouping dimension, so an agent immediately knows it produces a grouped revenue figure rather than a list of members, payments, or attendance. No sibling in the zen-planner set competes for this job, and the scope is unambiguous.

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 operating constraint clearly: 'One call covers one period; compare two months with two calls.' That tells the agent how to structure multi-period comparisons. It does not name an alternative tool or a when-not condition, but there is no adjacent revenue-reporting sibling to route against.

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