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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is covered. The description still adds real behavioral context beyond that: a stated cost of 20 credits, the fact that risk scoring and typo correction are gated behind paid plans, and that a normalized address is returned for duplicate detection. What it lacks is any mention of rate limits or latency/availability expectations for a network-dependent lookup.

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 dense paragraph that front-loads the core question (well-formed, deliverable, safe to accept) before enumerating supporting checks. Minor waste from the redundant title echo 'Email Validator: Email Validator is an email validation API' and the long run-on list of checks.

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?

An output schema exists, so return-shape explanation is unnecessary. The description is complete on capability scope, tier-gating, and cost — the things an agent needs to decide whether to spend credits. It stops short only on operational concerns like failure modes on unresolvable domains.

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?

There is a single required parameter with 100% schema description coverage, including an example, so the schema carries the semantics. The description adds nothing about input format or edge cases (e.g., whether to pass bare addresses vs. display names), which is the baseline-3 outcome for a fully documented single parameter.

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 names a specific verb and resource, then enumerates the exact checks performed: syntax, MX resolution with null MX and A-record fallback, SPF/DMARC, disposable/role/free-provider flags, and normalization. This level of detail lets an agent distinguish it from near-neighbors such as DisposableEmailChecker, MXLookup, or SPFValidator without opening any schema.

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?

Usage is implied by the breadth of checks (a general-purpose pre-acceptance validation), and the paid-tier note hints at capability limits. However, there is no explicit statement of when to pick this over DisposableEmailChecker or MXLookup, and no stated input prerequisites or failure behavior beyond the mentions of null MX and A-record fallback.

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