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

Annotations already mark the tool as destructive, non-read-only, and idempotent, so the safety profile is covered. The description adds useful behavioral context beyond those annotations: closing the session frees the GPU allocation and forgetting to close it incurs charges. This does not contradict 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 compact, front-loads the action, and then adds the billing consequence and auth requirement. Every sentence earns its place, though the parenthetical about api_key is somewhat redundant with the schema's required designation.

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?

The definition is adequate for a simple destructive action: it states the purpose, the resource affected, and the cost consequence, while annotations cover destructive and idempotent behavior. However, it does not mention return values, what happens to running workloads when the session is closed, or provide any session_id guidance, leaving some important operational context unclear.

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 description only elaborates on api_key, saying it is the key received at signup. session_id is not described in the schema or the description, and with only 50% schema description coverage the description should compensate for that gap but does not. Thus the agent is left to infer the meaning and format of session_id.

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 action ('セッションを閉じて') and the key outcome ('GPU の枠を返します'), so an agent knows this tool ends a session and releases resources. It is clearly distinguishable from siblings like create_session, get_session, and list_sessions, and even from interrupt by signaling a terminal close rather than a pause.

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 phrase '閉じ忘れは請求に乗ります' gives the main usage cue: call this when you are done with the session to avoid continued billing. It does not explicitly compare this tool to alternatives such as interrupt, nor state when not to use it, so it misses the full 'when/when-not/alternatives' bar.

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