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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the baseline is lower. The description adds meaningful operational behavior: it is pay-per-request and requires no API key, which helps an agent anticipate cost and authentication expectations before invoking the 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?

A single, front-loaded sentence that states the action, the resource, the protocol context, and the key operational constraints. There is no filler or redundant restatement of the tool name.

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 verification tool, the description covers the core action, payment model, and authentication requirement. It does not describe the return format or exact deliverability semantics, but the low complexity and existing annotations make this adequate.

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 already documents the single parameter with a description, format, and regex pattern, so coverage is essentially 100%. The description restates the purpose ('verify if an email address is valid') but adds no new parameter-specific semantics beyond what the schema provides.

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 and resource: 'Verify if an email address is valid and deliverable.' It clearly distinguishes this from sibling tools like mpp_email_finder and mpp_email_enrichment because it is about verification, not discovery or enrichment.

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 does not state when to use this tool versus alternatives. It gives operational context (pay-per-request, no API key required) but no explicit guidance on when to choose it over mpp_email_finder or mpp_email_count, or when not to use it.

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