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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds scoping context (syntax + MX only) and explicitly notes it does not detect disposable or role addresses, which is valuable beyond the annotations. It does not mention output format, but that is a minor gap for such a simple tool.

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?

Two sentences with no redundancy. The core purpose is stated first, and the exclusions/alternative are given in the second sentence. Every word contributes value.

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 with annotations covering safety and schema covering the parameter, the description is nearly complete. It lacks an explicit statement about the return format (e.g., boolean or result object), but the simplicity of the operation makes this a minor omission. The tool is fully usable as described.

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 schema description for the 'email' parameter already covers 'correct syntax and a resolvable domain' (100% coverage). The description adds the specific detail of an MX record check, which slightly enhances clarity but does not fundamentally change parameter understanding. Baseline 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 explicitly states the tool performs a lightweight email check covering syntax and MX record presence, and clearly delineates what it does not do (disposable/role addresses), distinguishing it from sibling tools like email_disposable and email_verify.

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?

It provides explicit guidance by naming the alternative tool (email_verify) for a combined check, and states exclusions (disposable/role) that signal when this tool is insufficient. This is direct routing to the correct sibling.

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