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

Annotations already declare readOnlyHint=false and idempotentHint=false, but the description adds a genuinely important behavioral fact: the plaintext secret is returned only this once (平文は今回だけ返します). This is critical operational context beyond the annotations. It stops short of 5 because it does not cover permissions or rate limits.

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?

Three compact parenthetical clauses; the purpose is front-loaded and there is little waste. Slightly telegraphic style but efficient and readable.

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?

No output schema exists, and the description supplies the key return-value fact (secret shown once only). It rounds out a creation tool adequately, though it omits any mention of the created key object's structure or scope.

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 100% schema description coverage, the schema already documents name, api_key, and environment. The description adds marginal value by noting environment maps to live/test production-vs-test semantics and that api_key is a key issued via the admin panel. Baseline 3 is appropriate since the schema does the heavy lifting.

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 (発行 = issue) and resource (API キー) and scopes it to 'このテナント' (this tenant). It is clearly a creation tool distinct from read/destructive siblings. It does not explicitly name a sibling to differentiate from, so it falls short of a 5.

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?

It conveys context — issuing 'もう 1 本' (one additional key) with live/test variants — but gives no explicit when-to-use/when-not guidance or alternatives. Usage is only implied, which matches the 3 baseline.

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