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

Annotations already declare readOnlyHint, idempotentHint and non-destructive, so safety is covered. The description adds genuine behavioral context beyond that: margin is only included when Stripe revenue is connected, which tells the agent why a field may be absent. It does not cover default date-range behavior, which is a minor remaining gap.

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 front-loaded sentence that lists exactly the breakdowns offered and qualifies the one conditional output. No filler and nothing buried.

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?

An output schema exists so return structure need not be explained, and annotations cover the safety profile; the description is therefore nearly complete. The one shortfall is that it is silent on the customer parameter's expected format and on default time window, which matter for correct invocation.

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 67%; start and end are documented as YYYY-MM-DD with patterns, but customer has no schema description. The description says nothing about the parameters, including what 'customer' accepts (id vs name) or what omitting start/end defaults to, so it adds no meaning beyond the schema. Baseline 3 is appropriate.

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 (one customer's cost) and enumerates the breakdown dimensions: total, by feature, by model, plus margin. It is clear what the tool returns, but it does not contrast itself with siblings like get_spend or get_margin, so the agent must infer the boundary.

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?

Usage is implied by the scoping phrase 'one customer', which suggests per-customer analysis versus the account-level siblings. However there is no explicit when-to-use, no named alternative (get_spend, get_margin, compare_models) and no exclusions or prerequisites.

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