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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false, and nothing in the description contradicts them. The description adds real behavioral context beyond the annotations: that ending frees a GPU slot and that leaving sessions open accrues billing charges, plus the api_key requirement.

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 compact clauses, front-loading the action and its effect, with the billing consequence and auth prerequisite appended parenthetically. No filler sentences.

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 two-parameter mutation with no output schema and annotations covering safety/idempotency, the description supplies the essential missing context (GPU release, billing cost of omission, auth needs). Only the session_id semantics remain unaddressed.

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 50%: api_key is documented in the schema and the description merely repeats that requirement, while session_id is undocumented in both places. The description does not compensate for the uncovered parameter, so this sits at the baseline for partial 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?

States a specific verb and resource ('セッションを閉じて' / close the session) plus the side effect of returning the GPU slot, which cleanly distinguishes it from siblings like get_session, list_sessions, and create_session. An agent can identify the operation without opening the schema.

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 billing warning ('閉じ忘れは請求に乗ります') gives a strong implicit reason to call this when finished with a session, but there is no explicit when-to-use/when-not or named alternative against the get/list/interrupt siblings. Usage is implied rather than directed.

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