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

With no annotations, the description carries the full burden of behavioral disclosure. It states the tool is 'Pure' (no side effects), free, and describes return components including a reason on failure. This is strong for a simple validation tool, though it doesn't mention auth or rate limits.

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, each informative; purpose and return behavior are front-loaded, and the free price is noted. There is no wasted text.

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?

Given the tool's simplicity, a single parameter, and no output schema, the description adequately summarizes outputs (normalized address, local-part, domain, failure reason). It could benefit from exact return format, but it's largely complete for a validation tool.

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 fully describes the single 'email' parameter with 100% coverage. The description adds context about normalization and return values, but no additional parameter-level specifics are needed, so it sits at the baseline.

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 states the tool validates and normalizes an email address, explicitly limiting to syntax/structure only. This distinguishes it from sibling tools like email_verify_check_mx and email_verify_check_spf, which handle deliverability checks.

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 phrase 'syntax/structure only' provides clear context on scope, implying this is for syntax validation rather than MX/SPF checks. However, it doesn't explicitly name alternatives or state when not to use it, so it's clear but lacks explicit exclusions.

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