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

With no annotations, the description carries the full behavioral burden and does so well: the code is never returned, resends are limited, the code expires, it consumes 1 email of the daily allowance, and a new code to the same address replaces the pending one. These are exactly the non-obvious traits an agent needs.

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?

Dense but front-loaded: the core action leads, followed by behavior, cost, edge case, and the follow-up call. Every sentence adds an actionable fact with no filler.

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 code-generation tool with no output schema, the description covers the return value ('Returns an id'), side effects, quota impact, and the required follow-up call. Nothing an agent needs to invoke it correctly is missing.

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 documents 'to', 'from', 'app_name', 'expires_in', and 'code_length' with defaults and ranges. The description adds no parameter-level detail beyond noting the usage cost, so the baseline 3 applies.

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 one-time verification code to an address') and immediately names the scenarios it serves (sign-up, sign-in, confirming an email). Clearly distinguished from the sibling verify_check, which is called afterward with the user-entered code.

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 routes the agent to the next step: 'Then call verify_check with what the person typed.' It also enumerates the triggering scenarios, so an agent knows exactly when this tool applies versus verify_check.

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