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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavior beyond them: results are ordered by date and include the extra cost incurred, which hints at a computed delta. It stops short of explaining how the delta is calculated or whether changes are grouped per product/supplier pair.

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?

A single tight sentence with the ordering and cost-delta details front-loaded and no filler. It is a fragment rather than a full clause, which slightly weakens readability but wastes nothing.

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?

There is no output schema, so the description carries the burden of describing return values; it does partially by stating date ordering and the extra cost. However, for a reporting tool it leaves the shape of results vague, and it never clarifies the scope of "same product code from the same supplier" or whether multiple rows are returned per change.

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% and the single month parameter is fully documented with a YYYY-MM format and example. The description only restates "this month" and adds no format, default, or boundary behavior beyond the schema, so the 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?

The description names a specific resource: price changes per product code per supplier within a month, ordered by date, with the cost delta. That is concrete enough to distinguish it from invoice-listing or month-summary siblings, though it is phrased as a noun fragment rather than a verb and never names the alternative tools.

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 is given and no alternative is named. An agent must infer from the phrasing alone that this is a read-only reporting query rather than the aggregation done by month_summary or the raw listing done by list_invoices.

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