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

Annotations already declare destructiveHint=true and idempotentHint=false, but the description adds genuinely non-obvious context the schema lacks: the exact return shape {verified, status, channel, charged} and the billing rule that the call is only charged when verified is true. It stops short of explaining what a repeated check does or what a failed/invalid code yields, which matters given destructiveHint=true.

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 with zero filler, front-loaded with the action and immediately followed by the payoff model. Every clause earns its place.

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?

With no output schema, the description usefully covers return fields and billing, so an agent knows what it gets back. It is thin on failure semantics (invalid code, expired code, repeat checks) and on how it relates to the sibling verification tools, which is the main remaining 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% and the schema itself documents the phone/email fallback rule and the 409 invalid_state case in depth. The description only restates the phone-or-email targeting at a high level, adding no format, precedence, or length semantics beyond what the schema provides.

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 names a specific verb ('Check') and resource ('a verification code submitted by a user') and identifies the lookup dimension (phone or email the code went to). An agent can distinguish it from send_verification (which sends) and get_verification (which appears to fetch state) reasonably well, though those highly similar siblings are never named explicitly.

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?

There is no explicit when-to-use or when-not-to-use guidance and no mention of the confusable siblings get_verification, fallback_verification, or send_verification. The only routing hint ('After a fallback, check by email') lives in the schema, not the description, so an agent must infer the workflow position on its own.

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