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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds substantive context beyond that: results are in the organization's default currency, and on non-Pro plans the call returns an explanatory message rather than data or an error — a behavior an agent could not infer from structured fields.

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 sentences with zero filler; the core capability and its output shape come first, with the plan caveat as a secondary clause. Every phrase carries information an agent needs.

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 correctly takes on the burden of naming the return values (total spend and expense count per period) and currency. It's nearly complete; the groupBy auto-detection behavior is left entirely to the schema, which is acceptable given full schema coverage.

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%, so dateFrom, dateTo, and the groupBy enum are fully documented in the schema. The description only implies date-range and per-period semantics that the schema already conveys, adding no new parameter detail.

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 ('Get total spend and expense count per period over a date range') and even specifies the currency semantics. It doesn't explicitly contrast with report siblings like get_revenue_report, but the resource is distinct enough that an agent can tell them apart.

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?

Provides a real eligibility condition (Pro plan and above), which helps an agent predict a non-data response on other plans. However, it offers no guidance on when to choose this report versus the other reporting tools or the individual expense tools.

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