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

Annotations declare a non-read-only, non-destructive mutation, and the description adds genuinely useful context beyond that: it will 'complete the add-email flow' on correct input and requires an authenticated Proof session. It omits failure behavior (wrong/expired code) and rate limits, but for a low-risk mutation it covers the important traits.

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 compact sections: the action sentence is front-loaded and the ACCESS block follows logically. Every sentence is functional, though the authentication aside is somewhat dense and could be tightened.

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 2-parameter mutation with no output schema, the description covers purpose, flow completion, and authentication prerequisites. It does not state what the tool returns or what happens to the email on success/failure, leaving a minor 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 both parameters are documented in the schema ('OTP code received via email', 'Add-email session ID'). The description adds no syntax or format detail beyond what the schema already provides, so the baseline of 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?

The description states a specific verb+resource ('Submit the OTP code to verify an email addition') and anchors it to a named flow ('add-email flow'), so an agent knows it completes a two-step email-add sequence. It does not explicitly distinguish itself from adjacent siblings like submit_verification_code or verify_2fa, which is the only reason it falls short of a 5.

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?

It gives clear operational context: the code comes from email, the session is an add-email session, and the tool finalizes the flow when correct. The ACCESS block explicitly explains prerequisites (Proof account, authentication via /mcp or start_login) and the re-call requirement. It stops short of explicitly naming when to choose it over submit_verification_code, so not a 5.

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