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

readOnlyHint=true already establishes the safety profile, so the bar is lower; the description adds real value by disclosing the authentication requirement, the session-opening behavior of start_login, and the fact that the call must be retried after an interactive flow. Minor gaps (no pagination or result-size guidance) keep it from 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?

Front-loaded with the operation and its result, then the access caveat. Every sentence earns its place, though the Claude-Code-specific parenthetical is slightly more verbose than the generic instruction that follows it.

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?

With no output schema, the description correctly carries the burden of saying what comes back ('domain metadata including verification status') and what is needed to call it at all (a Proof account). For a zero-parameter read tool this is close to complete, with only pagination/volume behavior left unstated.

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?

The tool takes zero parameters, so per the baseline this scores 4. There is nothing for the description to clarify beyond noting that the listing is implicitly scoped to the authenticated account, which it does.

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 and resource with scope: 'List all domains for the authenticated account.' It also summarizes the returned payload ('domain metadata including verification status'), which lets an agent distinguish it from the singular get_domain and from the many unrelated list_* siblings without opening a schema.

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 block gives explicit preconditions and an alternative path ('Authenticate this client... or sign in with start_login... then call this tool again'), which is genuinely actionable. It does not, however, say when to prefer this over get_domain (single-domain lookup) or check_domain_verification, so the sibling routing is only partially covered.

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