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

Beyond the annotations (readOnlyHint, destructiveHint), the description adds specific behavioral context: it explicitly states the tool does not open, charge, or settle a session, and it discloses the Authorization: Bearer header requirement. This adds meaningful transparency beyond the structured hints.

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 sentences, front-loaded with the core purpose, followed by essential clarifications. No wasted words; the description is compact and well-organized.

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?

Given the tool's simplicity (no parameters) and the presence of an output schema, the description is complete. It covers the purpose, time window, side-effect guarantees, and authentication requirement, leaving no significant gaps.

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 zero parameters, the schema fully covers parameter semantics. The description doesn't need to explain parameters, and it adds the important context that the usage data is for the current 24-hour window, which serves as a semantic constraint.

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 states the action (Read), the resource (aggregate Direct Session usage), and the scope (current 24-hour window). It distinguishes itself from sibling get_ tools by naming the specific data type being retrieved.

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 provides clear context for when to use the tool: it is a read-only, gated-discovery view for checking usage without opening or charging a session. It does not explicitly name alternatives, but the 'does not open, charge, or settle a session' clause gives a strong negative guideline.

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