Verify an e-mail address

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

Annotations cover safety (readOnly, idempotent, non-destructive, openWorld), and the description adds genuinely new behavioral context: a ~5 second latency, a 1-credit cost, and the degraded-mode contract where SMTP cannot connect (reason smtp_unreachable, catch_all null). This is exactly the kind of operational detail annotations cannot carry.

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?

One dense paragraph with the core action front-loaded, followed by the fallback behavior, the return shape, and the cost/latency terms. No sentence is filler; each adds a distinct fact an agent needs.

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?

With no output schema, the description steps in to name the returned fields (validity, score, reason codes) and their possible values, and it documents the runtime and billing side effects. Everything needed to call and interpret the result is present.

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 there is a single parameter with its own example and length bounds, so the schema does the heavy lifting. The description adds no formatting or syntax nuance beyond what the schema already documents, so the baseline 3 applies.

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?

States a specific verb (verifies) and resource (an e-mail address) and enumerates the exact checks performed: syntax, disposable domain, role account, MX records, plus SMTP mailbox and catch-all. An agent can distinguish this from the provisioning/search siblings purely from the description.

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 context for using it is implied by the tool's narrow subject (verifying a single address) and the sibling names are clearly unrelated, but the description never states when to reach for this tool versus an alternative, nor any preconditions beyond the implicit requirement of an address.

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