List usage events

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

Annotations already establish read-only, idempotent, non-destructive behavior. The description adds valuable context beyond annotations by stating the required scope 'usage:read' and explaining that the sum of a call's events equals the debited amount. No behavioral contradiction exists.

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?

The description is only two short sentences plus a scope requirement, with the core meaning front-loaded. Every sentence earns its place: the billable-line nature, the session_id use case, the cost-sum invariant, and the required scope.

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 7-optional-parameter list tool with no output schema, the description covers the essential semantics: what is returned, why it matters, and what authorization is needed. It does not describe pagination or response field format, but the schema already documents cursor parameters, and the core intent is clear.

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?

With 86% schema description coverage, the baseline is already strong. The description adds meaning to the session_id parameter by clarifying it comes from a call record and that summing events for that session reveals the exact debited cost, which goes beyond the schema's minimal field description.

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 clearly identifies the tool's output as 'Every billable line, itemised' and ties it to call-level cost breakdown via session_id filtering. It conveys the resource and purpose without ambiguity, though it does not explicitly name or contrast any sibling tool such as get_usage_summary.

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 description gives a concrete usage pattern: filter by session_id to see exactly what one call cost and why. It does not explicitly state when not to use this tool or recommend an alternative, but the session_id use case is clear context for when this tool is appropriate.

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