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

Annotations already declare readOnlyHint and openWorldHint, and the description adds genuinely new behavioral facts: the response contains addresses only with no source attribution, and calls are metered at $0.05 USDC per successful call via x402 on Base or Solana when no API key is supplied. That cost and output-content disclosure is exactly the kind of context annotations cannot carry; only failure behavior is unstated.

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?

Three tight sentences, front-loaded with the resource and immediately followed by the output-scope caveat. The payment sentence is boilerplate but earns its place by explaining the unauthenticated cost model.

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 compensates by stating what the response does and does not contain, and it discloses the paid-access path that would otherwise surprise an agent. For a one-parameter read-only lookup, nothing essential is missing.

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?

With a single parameter at 100% schema description coverage, the schema already explains that the input may be a domain, URL or email address on it. The description adds only the loose framing 'associated with a domain' and no format or normalization detail beyond the schema, so baseline 3 applies.

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 names a specific resource and its scope: 'Every email address associated with a domain', which is clearly distinct from siblings like domain_ips, domain_urls and domain_whois. It does not explicitly name those siblings, so an agent must infer the routing, but the verb+resource pairing is unambiguous.

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?

There is no statement of when to use this versus osint-email, domain_urls or domain_ips, and no prerequisites or exclusions are given. The only context offered is billing mechanics, which is not usage guidance for tool selection.

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