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

There are no annotations, so the description carries the burden. It does disclose that this starts a stateful session and requires prior authentication, but it does not explain side effects (e.g. whether a pending verification is created), idempotency, or what happens if verification is already in progress.

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 compact and front-loads the core action before the access note. The access wording is slightly convoluted, but no sentences are wasted and the structure is easy to scan.

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 stateful starter with no output schema and no annotations, the description should explain what the caller receives and what to do next (e.g. polling check_user_domain_verification). It covers authentication well and parameters completely, but the missing post-call workflow leaves a real 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 coverage is 100%, with both domain and channel already described in the schema, so the baseline is 3. The description's mention of DNS/HTTP loosely maps to the channel enum but adds no new parameter-level detail beyond the schema.

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 action ('start a self-service domain verification session') and the mechanism (proof via DNS or HTTP challenge). It clearly identifies the resource, but it never explicitly distinguishes this from closely named siblings like start_domain_verification or start_domain_email_verification, so it earns a 4 rather than 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?

The ACCESS note gives concrete context: the caller needs a Proof account and an authenticated client, and says to call start_login first if not authenticated. This is clear usage guidance, but it stops short of stating when to choose this tool over alternative verification tools or when not to use it.

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