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

Annotations only declare readOnly=false and destructive=false. The description adds real behavioral context beyond that: it triggers an outbound OTP email, returns a session ID rather than finalizing the add, and requires an authenticated Proof account. It does not state rate limits or OTP expiry, so not a 5.

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 tight sentences front-load the action and its effects, and the access note is separated into its own paragraph. No filler or repetition.

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 one-param, no-output-schema step in an email-adding flow, the description covers action, side effect, return artifact, and auth prerequisite. Only the downstream verification tool name is missing, which is minor.

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% for the single required email parameter, so the schema already carries the semantics. The description's mention of 'the email' adds no format or constraint detail beyond the schema; baseline 3 is appropriate.

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+resource ('Start adding a new email address') and the immediate side effect (sends OTP) plus return value (session ID). It is clearly distinguishable from list_emails/remove_email, though it does not name the obvious sibling start_add_phone it mirrors.

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 gives the prerequisite (a Proof account, authentication via /mcp or start_login after which the tool can be called) and implies the follow-up verification step via 'session ID to verify with.' It stops short of naming verify_email_otp as the continuation, but the when-to-use context is clear.

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