email_validate

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

No annotations are provided, so the description carries the full burden. It discloses cost ($0.005 per call), technical method (DNS-over-HTTPS), data persistence (nothing stored), caching (up to 1 hour), and the meaning of the 'deliverable' flag. This is comprehensive.

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?

Every sentence is informative: cost, purpose, technical detail, limitation, and use cases. The description is front-loaded with the most critical information (cost and action) and contains no filler. It is appropriately sized for the tool's complexity.

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?

Despite no output schema, the description explains the return values (parsed domain, sorted MX hosts, deliverable flag) and their meaning. It covers cache behavior, cost, and limitations. With only one simple parameter, the description is fully complete.

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 input schema already describes the single required parameter 'email' as 'Email address to validate.' The description does not add new semantic details about the parameter beyond what the schema provides. With 100% schema coverage, a baseline 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 clearly states 'Validate an email address: syntax check plus live MX-record lookup.' It specifies the verb (validate) and resource (email address), and the sibling tools are all unrelated (crypto, finance, weather, etc.), so there is no confusion.

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 explicitly lists use cases: 'Use for lead cleaning, signup validation, and contact verification by agents.' It also notes a key non-use: 'It does NOT verify the mailbox exists.' However, no explicit alternatives are given, though there are no competing email tools.

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