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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior. The description adds meaningful unannotated context by revealing that the tool depends on the external IPQualityScore API and requires a user-supplied key. It does not mention rate limits or third-party data handling, but the authentication dependency is the key behavioral disclosure beyond annotations.

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 three sentences with a front-loaded purpose, a compact usage example, and a necessary credential requirement. Every sentence earns its place, and there is no filler or repetition of annotation data.

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 explains the return value in prose (fraud score plus deliverability, SMTP, and DNS signals) and covers the required external API key. It does not describe exact response shape or error conditions, but for a two-parameter, read-only tool this is still adequately complete.

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%: both email and _apiKey are fully documented in the schema, including where to obtain the IPQualityScore key. The description restates the example and key requirement but adds no new semantic meaning beyond what the schema already provides, so the baseline score of 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 opens with a specific verb-plus-resource statement ('Email fraud & deliverability check') and enumerates concrete behaviors: validates the address, detects disposable/temporary addresses, flags data-leak exposure, and returns a 0-100 fraud score plus SMTP/DNS validity signals. This clearly differentiates it from sibling tools like check_ip, check_phone, and check_url.

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 description provides clear context for when to use the tool: whenever an email address needs fraud, deliverability, or validity assessment. It implies a natural separation from sibling resource-specific checkers, but it never explicitly states when not to use it or names alternatives, so it falls just short of full routing guidance.

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