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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds the meaningful nuance that this is an aggregation over multiple transactions rather than a narrative description. It does not disclose return shape, totals vs averages, or behavior when no transactions match the range.

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, front-loaded with what the tool does, and the second sentence is a legitimate exclusion rule rather than filler. The second sentence is slightly wordy ('not a narrative description of one') but earns its place by preventing misuse.

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 simple read-only aggregation with three fully documented parameters and no output schema, the description covers purpose, scope, and the main misuse case. Minor gap: no indication of what the aggregate response contains (e.g. per-group totals), which would matter given there is no output schema.

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%: startDate/endDate formats and the groupBy enum are fully documented in the schema. The description restates the date range and the category/merchant grouping without adding syntax or constraint details beyond the schema, so the baseline of 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?

The description gives a specific verb and resource ('Get an aggregate spending total') plus the aggregation dimensions (grouped by category or merchant). It explicitly carves itself away from single-expense description, which helps against get_expense_detail. However, it does not differentiate from other aggregate siblings like get_spending_trends or get_top_merchants, so it falls short of full sibling differentiation.

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?

There is an explicit when-not-to-use clause: for describing a single already-open expense, use the provided expense data instead. That is a real routing rule. It stops short of naming the alternative tool to use for trend or per-merchant breakdowns, which the sibling list suggests would be useful.

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