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

Annotations already declare readOnly, openWorld, idempotent, and non-destructive behavior. The description adds meaningful behavioral context beyond that: it performs MX lookup, flags disposable/free/role accounts, suggests typo corrections, returns a composite score, and importantly does NOT perform a live SMTP probe. It also notes demo mode is allowed, which is useful operational context not captured in 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 a single compact sentence that front-loads the core action and then efficiently lists the key checks and limitations. Every clause adds information: the validation scope, the behavioral boundary (no SMTP probe), and the demo-mode allowance. There is no filler.

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?

The description is adequate for a moderately complex read-only tool: it explains what checks are performed and the composite score, and the annotations cover safety. However, with no output schema, the description does not fully characterize the return shape beyond the score/flags, and the check_dns parameter remains unexplained. These gaps make it complete enough to use but not fully self-sufficient.

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 only 50%: 'email' is described, but 'check_dns' has no schema description and no description-level explanation. The description mentions 'MX lookup' but never links it to the check_dns parameter or explains that toggling check_dns controls DNS checking. With one undocumented parameter and no compensating explanation, the description fails to fully convey parameter semantics.

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?

Description states a specific verb ('Validate') and resource ('an email address') and enumerates exactly what the validation covers: RFC syntax, MX lookup, disposable/free/role-account flags, typo correction, and composite deliverability score. This clearly distinguishes it from sibling tools like email_smtp_probe or email_disposable by positioning it as the comprehensive validation entry point.

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 implies when to use this tool by presenting it as full email validation and by explicitly noting 'no live SMTP probe,' which hints that live probing is out of scope. However, it does not name sibling alternatives such as email_smtp_probe for live deliverability checks or email_disposable/email_free_provider for narrower checks, so usage guidance remains implied rather than explicit.

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