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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and a closed world, so safety is covered. The description does add useful behavior beyond that: this returns aggregated figures grouped by month/category/vendor in each currency rather than raw transactions. It still omits default date-window behavior, whether results are bucketed or summed, and any currency-conversion semantics.

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?

One short sentence, front-loaded with the grouping dimensions. The trailing '— the numbers behind the charts' is decorative but cheap and reinforces that this is an aggregated report.

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 must carry return-shape information, and it does so only partially by naming the grouping dimensions. It leaves open what happens with no dates and how results are shaped, which is a real gap for a reporting tool surrounded by many similar siblings.

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% and both parameters are documented as ISO YYYY-MM-DD dates, so baseline 3 applies. The description adds only the implied 'by month' grouping, not any clarification of inclusive/exclusive bounds or open-ended filters.

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 the resource (spending) and the aggregation axes precisely: by month, category, vendor, per currency. That is much more than a restatement of the name, but it never distinguishes this report from close siblings like purch_year, purch_card_costs, or purch_purchases, so an agent cannot route between them on description alone.

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?

No when-to-use guidance and no named alternative. Both parameters are optional, yet the description says nothing about the default range when from/to are omitted, which is exactly the decision an agent must make before calling.

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