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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful context by identifying the returned metrics and flagging connection time as the basis for billing, but it does not describe error behavior, response structure, or any operational side effects beyond the annotations.

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 a single, front-loaded sentence that directly names the return values and the authentication requirement. There is no filler or redundant verbiage, and the key context is placed prominently.

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 low complexity (one simple parameter, no nested objects, no output schema), the description adequately covers the tool's purpose, required input, and return values. It does not specify units for connection/speech time or response format, but the essential information an agent needs to call it correctly is present.

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 description coverage is 100%, and the single api_key parameter is already documented as 'API キー (sk_live_…)'. The description adds the detail that the key is obtained at signup, which is mildly helpful, but it does not materially expand on the schema's semantics. Baseline 3 is appropriate given the high schema coverage.

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 states a specific verb ('返します' – returns) and a clearly defined resource: current-month connection time, speech time, session count, and plan limits. This is sufficiently distinct from sibling tools like get_account, get_session, list_sessions, and list_plans, so an agent can infer which sibling to choose.

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 explains what the tool returns and notes that an api_key is required, but it gives no guidance on when to choose this tool over alternatives such as get_account or list_plans. There are no explicit usage contexts, exclusions, or when-not-to-use conditions.

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