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

Annotations already declare destructiveHint=true, idempotentHint=false and openWorldHint=true, and the description adds real value beyond them: it discloses that TextKit generates the code, that expiry is 10 minutes, that attempt limits are 5, and that SMS-pumping/email-bombing abuse is blocked. What's missing is any statement of what the call returns (a verification id?) and whether rate limits or costs apply per send.

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 dense sentence that front-loads the action and the two channels before the lifecycle details. Efficient, though the clause list about expiry/limits/abuse is packed tightly enough to be slightly hard to scan.

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 an 8-parameter, zero-required, mutating tool with no output schema, the description covers the send lifecycle well but omits the return shape — critically, whether a verification id/handle comes back for a later check_verification call. That omission is the main completeness gap.

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 description coverage is 100%, so the schema already explains phone/email/channel/from/user_ip/idempotency_key in detail; the description only restates the channel mapping. Baseline 3 is appropriate — it adds little meaning the schema does not already carry.

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 — sending a one-time verification code (OTP) — plus the two delivery channels (SMS text or email). The OTP framing implicitly separates it from the generic send_message sibling, but no sibling is named explicitly, so an agent must infer the boundary with check_verification/fallback_verification.

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?

Usage is only implied: 'to a phone number by text, or to an email address with channel "email"' hints at channel selection, but there is no explicit when-to-use, when-not-to-use, or pointer to the natural follow-up (check_verification) for validating the code.

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