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

With no annotations, the description carries the behavioral disclosure burden. It discloses the side effect of sending a verification code to an admin email, the authentication prerequisite, and the need to call again after establishing a session. It does not cover potential errors or response behavior, but the disclosed traits are accurate and useful.

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?

The action is front-loaded in one clear sentence, and the ACCESS block provides necessary authentication guidance without excessive verbosity. It is slightly longer than strictly necessary, but every sentence contributes operational value.

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?

Given moderate tool complexity, no annotations, and no output schema, the description covers purpose, mechanism, and authentication prerequisite adequately. It does not describe the response or next steps (e.g., confirming the code), but the schema covers parameters and an agent has enough information to invoke it correctly.

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% with descriptions for both id and email_prefix, including the enum and default. The description adds only marginal context ('standard admin email address') beyond what the schema already documents, so the baseline score 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?

Description states a specific verb ('Start'), resource ('domain verification'), and method ('via corporate email'), with a concrete behavioral detail: sends a verification code to a standard admin email at the domain. This clearly distinguishes it from siblings like start_domain_verification or start_user_domain_verification by its email-specific mechanism.

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?

The description clearly implies when to use it: to start domain verification specifically through corporate email. It also provides important prerequisite context by explaining the access requirements (needs a Proof account, authenticate or sign in via start_login, then retry). It does not explicitly name alternative tools or exclusions, but the context is unambiguous enough for an agent.

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