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

With no annotations, the description carries the full burden of disclosure. It clearly states the scope (syntax, domain, MX) and the absence of SMTP verification, which is a behavioral limitation. However, it doesn't mention return format or error behavior, so it is not fully transparent but sufficiently so for a simple validation 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 sentence that front-loads the purpose and includes a crucial limitation. Zero wasted words; every clause adds information.

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 one-parameter validation tool with no output schema, the description is adequate. It tells the agent what it validates and what it doesn't. It doesn't specify the return type, but for a simple validator the result is likely boolean/status; this is a minor gap given the tool's simplicity.

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% and the schema description already says 'Email address for syntax, domain and MX validation.' The tool description adds no new parameter-level detail beyond that. Baseline 3 is appropriate since the schema fully covers the 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 uses the specific verb 'Validate' with the resource 'email', and enumerates exactly what is validated (syntax, domain, MX records). It also explicitly distinguishes this from SMTP mailbox verification, so an agent can clearly tell it apart from any similar-sounding tools.

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 'for basic automated checks' gives context on when to use it, and the exclusion 'without SMTP mailbox verification' tells the agent what this tool does NOT do, implying when a more thorough verification would be needed. It doesn't name alternatives, but the limitation is explicit.

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