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

Annotations already mark this as non-read-only and idempotent; the description adds real side effects: it returns the link and sends an email, and opening the link consumes free-tier quota. It also notes the api_key requirement, which is useful beyond the schema. No contradiction with 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?

Two concise sentences with the core action first and the behavioral caveat second. The parenthetical auth note is relevant, though the quota phrasing ('無料枠の上限になります') is slightly awkward.

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 one-parameter tool with no output schema, the description covers the action, target, side effect, auth requirement, and quota impact. It could add what happens for already-confirmed tenants, but nothing essential is missing for a basic 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?

The single api_key parameter is already fully described in the schema (100% coverage). The description adds that the key is the one received at signup, which clarifies where to obtain it.

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 ('再発行して返し、メールにも送ります') tied to a precise resource (confirmation link for email-unconfirmed tenants). It clearly distinguishes this tool from siblings like signup or create_session by identifying the unique action and target.

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 defines the applicable context: use when the tenant's email is unconfirmed. It does not name alternatives or explicitly state when not to use it, but the sibling list contains no competing resend/verification tool, so the context is sufficient.

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