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

Beyond the annotations, the description discloses the rate limit (5 OTPs per 10 min per IP), OTP validity window, that step 2 irreversibly creates a tenant plus an ECDSA P-256 VAPID keypair, and that the endpoint is public with no API key. These are behavioral facts the structured fields do not carry.

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 two-step mechanism and sibling exclusions are front-loaded, and every clause carries operational information. It is dense to the point of being a single long sentence, which slightly hurts scannability, but nothing is wasted.

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?

A non-idempotent, open-world mutation tool with no output schema is fully covered: the description supplies the return payload shape (ok, step, tenant, app fields including the API key and VAPID key), the rate limit, and the irreversibility warning. An agent has everything needed to call it correctly and interpret the response.

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 100%, so the baseline is 3; the description earns above that by explaining the conditional coupling of otp_code with password and name and by tying each parameter set to a step. It does not add format constraints beyond what the schema already states (length minimums, HTTPS origin).

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 concrete verb and resource (register a new account via OTP) and spells out the two-step protocol explicitly. It names the sibling tools it is not (login_existing_account, create_app), so an agent can distinguish it from all 15 siblings 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?

Explicit when-to-use ('only for brand-new user signups') and when-not-to-use rules with named alternatives for each case. The two-step invocation condition (omit otp_code first, pass it on the second call) is stated as a routing rule, not left to inference.

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