start_user_domain_verification

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

With no annotations, the description carries the full burden. It discloses that this starts a verification session and requires authentication, which is useful, but it does not mention what the response contains, whether repeated calls create multiple sessions, or how the challenge is surfaced to the user. These are notable gaps for a state-changing tool.

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 description is reasonably concise and front-loaded with the core purpose. The access paragraph is slightly awkwardly phrased but contains necessary operational details, so it earns its place despite minor verbosity.

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?

The tool has no output schema and no annotations, so the description needs to give the agent enough to understand the full workflow. It explains the initial step and access requirements, but does not mention next steps like checking verification status or completing the challenge, which are relevant given the sibling tools and the multi-step nature of domain verification.

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 parameters are already well documented. The description adds a small amount of context by mentioning DNS or HTTP challenges, but this merely mirrors the channel enum rather than adding new semantic meaning. 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?

The description clearly states the action ('Start'), the resource ('domain verification session'), and the mechanism ('DNS or HTTP challenge'). However, it does not explicitly differentiate from the sibling tool start_domain_verification, so it stops 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?

Provides clear context on when to invoke the tool: a Proof account is required, and the agent must either set PROOF_API_KEY or authenticate via start_login. It does not explicitly list alternatives or exclusions, but the access conditions are specific and actionable.

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