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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds the api_key authentication requirement, which is beyond what annotations provide. It does not contradict any annotation, and while it adds the auth context, it omits details like whether the session can be queried after it ends or error behavior for invalid session_id.

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?

A single, tightly-packed sentence that front-loads the return values and appends the auth requirement as a parenthetical. No filler or redundancy, though the two distinct pieces of information (return payload and auth prerequisite) could be structured slightly more explicitly.

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?

As a read-only state inspection tool with no output schema, the description compensates well by enumerating the return fields (state, queue length, connection time, expiry). However, the session_id parameter is left undocumented, and there is no guidance on edge cases like expired sessions or invalid keys, which an agent might reasonably need for a complete call.

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 described in the schema ('API キー (sk_live_…)') and the description reinforces its origin ('signup で受け取ったキー'), adding value for that parameter. However, session_id has no schema description and the tool description provides no semantics for it, leaving a gap that neither the schema nor the description fills.

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 ('返します' - returns) with a clear resource (session state) and enumerates the exact fields returned: active/ended status, queue length, connection time, and expiry. This distinguishes it from siblings like create_session, end_session, and list_sessions, and reinforces the title without being tautological.

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 discloses a prerequisite: api_key is required and must be the one received at signup, which is useful context for invocation. However, it does not explicitly differentiate this tool from alternatives such as get_account or list_sessions, nor does it state when an agent should prefer get_session over list_sessions for inspecting a single session's state.

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