list_domains

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

readOnlyHint=true already declares the safety profile, so the bar is lower; the description still adds genuine context by disclosing the auth requirement to reach this tool and by describing the returned content (domain metadata with verification status). It stops short of noting pagination or result limits, but the added auth and return context is substantive.

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 core action in one sentence, then a clearly separated ACCESS block. The access note is slightly verbose but earns its place because it names the exact remediation path (API key or start_login). No filler.

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 read-only, zero-parameter list tool with no output schema, the description covers what is returned ('domain metadata including verification status') and how to gain access. Little an agent needs is missing; only sibling disambiguation and any pagination/count behavior are absent.

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 there is no parameter semantics to explain; the baseline of 4 applies. The description correctly implies no arguments are needed to enumerate all domains.

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 ('List all domains') scoped to 'the authenticated account', plus what it returns ('domain metadata including verification status'). It reads clearly against siblings like get_domain or add_domain, though it never names them explicitly, so it falls 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?

The ACCESS block gives real preconditions (needs a Proof account, set PROOF_API_KEY or sign in via start_login). However it frames these as authentication steps rather than when-to-use-vs-alternatives guidance, and never distinguishes this from get_domain or list_verified_users. Usage is implied rather than directed.

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