Describe Session Token Usage

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

Beyond the readOnly/idempotent annotations, the description discloses precisely how the tool works: it fetches raw event messages, filters to inference-succeeded/failed turns, returns one entry per turn plus a summary, and excludes non-inference events. This gives the agent a robust mental model of the tool's behavior and output structure.

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 three tight sentences. The first sentence is a clear, front-loaded summary; the following sentences add necessary behavioral detail without redundancy. Every sentence earns its place.

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, single-parameter tool with an output schema, the description explains the essential behavior, filtering logic, and return shape. It is complete enough for an agent to select and invoke the tool correctly without ambiguity.

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?

The single parameter `session_id` is fully described in the schema, and the tool description reinforces it ('single agent session'). With 100% schema coverage, the description adds little beyond the schema, which is acceptable but does not elevate the score.

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 uses a specific verb ('Break down') and a clearly defined resource ('a single agent session's token usage per inference turn'), immediately establishing what the tool does and distinguishing it from broader token-usage tools. Even without naming siblings, the scope is unambiguous and narrowly defined.

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 first sentence clearly contextualizes when to use this tool: when you need a per-inference-turn token breakdown for a single session. However, it does not explicitly mention alternative tools or exclusions, so it stops short of the highest level of guidance.

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