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

Annotations only declare readOnlyHint=false and destructiveHint=false, so the description carries the rest: it discloses that the call creates a persistent verification record (a write) and that the response contains DNS/HTTP instructions for the customer. The authentication requirement is stated, which annotations do not cover. It does not address repeat calls, idempotency, or expiry of the created record.

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 brief paragraphs, purpose front-loaded, with the access caveat clearly separated. Every sentence carries information; nothing is padded. The ACCESS block is slightly jarring stylistically but 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?

For a 3-parameter, no-output-schema tool, the description covers what it does, the auth prerequisite, and what the caller receives (instructions). The main gap is the absence of any guidance on the follow-up tool to poll or complete verification, which matters given the dense verification-sibling cluster.

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 all three parameters are documented in the schema, so the baseline is 3. The description's mention of 'DNS/HTTP instructions' loosely maps to the verification_method enum but adds no format or default detail beyond what the schema already says.

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 ('Start') and resource ('B2B domain verification') and adds the concrete outcome: creates a verification record and returns DNS/HTTP instructions. The 'B2B' qualifier helps separate it from start_domain_email_verification and start_user_domain_verification, but it never explicitly names check_domain_verification or verify_domain, so the routing among near-identical siblings is left partly to inference.

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?

Gives an explicit prerequisite (needs a Proof account) and an actionable remediation path (authenticate via /mcp, then call again), plus a useful exclusion: 'start_login does NOT open this tool.' What it lacks is any statement of when to prefer this over verify_domain, check_domain_verification, or the reinitiation vs. checking flow.

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