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

Beyond the annotations, the description discloses meaningful behavior: live MX/deliverability checks, edge compute and DoH as the source, a per-call cost, and the HTTP method. This adds operating context that annotations alone do not provide, and it does not contradict the readOnly/idempotent hints.

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 a single, information-dense sentence with no filler. It front-loads the core purpose and appends only high-value operational details: source, cost, and endpoint.

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 single-parameter read-only tool, the description covers the essential behavior and expected outcomes (syntax, MX/deliverability, disposable-domain flag). There is no output schema, so a bit more detail on the exact response structure could help, but the described checks are sufficient for an agent to invoke and interpret the result.

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 for the single email parameter is 100%, so the schema already fully documents the input. The description adds no parameter-level detail, but the schema provides an example and clear meaning, meeting the baseline expected for high schema coverage.

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 clearly identifies the resource (email) and operation (validation), and enumerates concrete aspects: syntax check, live MX/deliverability, and disposable-domain flag. This distinguishes it from the broad set of data-lookup sibling tools without ambiguity.

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 makes the use case clear: validate an email address with syntax, MX, and disposable-domain checks. While it does not explicitly name alternatives or exclusions, no sibling tool directly competes, so an agent can infer when to select this tool confidently.

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