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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered; the description adds the meaningful boundary that only aggregate daily counts are available (no per-endpoint breakdown). It does not address stats freshness or any delay between usage and reporting, which is the main remaining behavioral unknown for a usage-stats tool.

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 short sentences, front-loaded with the scope restriction and the returned fields, then the parameter note. Zero filler.

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 rich annotations, an output schema documenting return shape, and one fully described optional parameter, the description covers what an agent needs. The only gap is data freshness/latency, minor given the rest of the structured metadata.

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 there is a single optional parameter already fully documented with bounds (1-366) in the schema. The description restates the same semantics ('last N days instead of the current cycle') without adding format or edge-case detail, so 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?

States a specific resource and scope: 'API usage statistics (aggregate daily request counts only)' with the fields returned (cycle total, allowance, remaining, per-day). The 'aggregate daily request counts only' qualifier implicitly separates it from per-request history tools like get_billing_history, but no sibling is named explicitly.

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?

The only usage guidance is about the optional 'days' parameter ('returns the last N days instead of the current cycle'), which describes parameter behavior rather than when to choose this tool. Nothing tells the agent when to prefer get_usage_stats over get_amount_owed or get_billing_history.

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