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 mentions the outputs (deliverability signals) and hints at validation, but doesn't state potential side effects (e.g., sending network requests, rate limits, or data privacy considerations). It doesn't disclose whether it performs only syntax checks or actual delivery testing, which could affect trust.

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, focused sentence that front-loads the main action and states the key outputs. It's efficient, though it could add a brief usage hint without becoming verbose.

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 simple single-parameter validation tool with no output schema, the description is adequate: it specifies the input and the nature of the output. However, it lacks detail on the exact return structure (e.g., is the result a boolean, an object, or a string?) and does not clarify whether the validation is synchronous or asynchronous, which an agent might need to know.

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 coverage is 100%, so the schema already documents the 'email' parameter well. The description adds no extra semantics beyond what the schema provides, so a baseline score of 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 states a clear, specific action ('Validates an email address') and a concrete resource ('an email address'), with the key output signals ('valid/invalid/risky, catch-all detection, provider, confidence'). It distinguishes from sibling tools like run_email_finder (finding addresses) and run_email_enrichment (enriching data), but it doesn't explicitly name them.

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 usage (when you need to validate an email and check deliverability), but gives no explicit guidance on when to use this versus similar sibling tools like run_email_enrichment or run_email_finder. For a simple validation tool, the context is reasonably clear, not misleading.

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