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

With no annotations, the description carries the burden and does disclose meaningful behavior: the code is sent to the account email (the caller cannot choose a destination), it expires in 10 minutes, and there are 5 attempts. It omits whether calling again resends or invalidates an outstanding code, and says nothing about rate limits or failure/error modes for a mutation that produces an email.

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 short sentences, both earning their place: the first states the action plus its operational constraints, the second states the required follow-up. Nothing is repeated from the schema or padded.

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 low-complexity, zero-required-parameter starter tool with no output schema, the description covers the action, the constraints that shape agent retry logic, and the mandatory next call. It lacks only what a successful response looks like (masked email, expiry echo) or what error states to expect.

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?

There is a single optional parameter, idempotency_key, and the schema already documents it at 100% coverage with a clear retry instruction. The description adds no parameter-level meaning, which matches the baseline of 3 when schema coverage is high.

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 ('Email a 6-digit code to the account email') and implicitly scopes the destination to the account's own address. The second sentence names the sibling confirm_email_verification and its role, so an agent can separate the two-step flow from the other verification siblings (start_dns_verification, get_verification) without opening a 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?

Explicitly tells the agent this is step one of a sequence and that confirm_email_verification must be called next with the code, which is the key routing rule. It does not state preconditions (e.g. authenticated account, no verification already pending) or when to prefer start_dns_verification instead, so it stops short of full when/when-not guidance.

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