Verify one email address

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

Annotations already mark this as read-only, idempotent, and non-destructive. The description goes beyond annotations by detailing the result shape, the meaning of each action value, the behavior of checks.smtp across tiers, and the credit cost of the hosted SMTP probe. This gives the agent a rich understanding of side effects and tier-dependent behavior.

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 dense but every sentence earns its place: core purpose, result format, action semantics, tier behavior, and credit cost are all covered. It is front-loaded with the primary use case and flows logically into operational details without fluff.

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 having no output schema, the description fully documents the return shape and the meaning of each action. It also covers tier selection, credit cost, and default behavior. An agent has everything needed to call the tool correctly and interpret its result.

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 description coverage is 100%, so the schema already documents both parameters. The description adds meaningful context for the 'hosted' parameter by explaining when the hosted SMTP probe is used, when the free DNS tier is used, and that it costs 1 credit. This is useful information beyond the schema's simple boolean description.

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 specific verb and resource: 'Check whether an email address can receive mail before sending to it.' It clearly identifies the tool's purpose and differentiates it from siblings like verify_batch by focusing on a single email address and providing a concrete decision outcome (send/hold/kill).

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 gives clear context for when to use the tool ('before sending to it') and explains the hosted versus free DNS tier behavior. It does not explicitly name alternatives or state when not to use it, but the singular-versus-batch distinction with verify_batch is strongly implied.

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