Verify an email address against mailbox and domain reference data

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

With no annotations, the description carries the full burden. It discloses the return values (confidence score 0-100 and result codes) and clarifies a key limitation (deliverable does not confirm control). It does not mention error handling, rate limits, or side effects, but for a read-only verification tool, these are minor. This is solid transparency for the core 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 three sentences, front-loading the core purpose, then covering return values, recommended usage, and a critical caveat. There is no fluff or repetition; each sentence earns its place. The structure is well organized and easy to scan.

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 single-parameter tool with no output schema, the description covers the what, the return type, when to use, and a limitation. The only gap is not detailing the specific result codes or their meanings, but this may be acceptable given the lack of an output schema and the tool's simplicity. It is largely complete for an agent to call correctly.

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 parameter is well-described ('Email address to verify'). The description adds semantic nuance by clarifying that the email is checked for deliverability, not just format, which goes beyond the schema's literal definition. This adds value without redundancy.

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 action ('Checks whether an email address is deliverable, not merely well-formed') with a clear resource (email). It distinguishes from siblings by focusing on deliverability, not format validation, and the sibling names (verify_phone, verify_postal_address) clearly differ. It is unambiguous and specific.

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 provides explicit when-to-use guidance ('Call this before sending anything time-sensitive or before treating an email address as a verified contact channel') and an explicit exclusion ('Do NOT use this as an identity check'). It also explains why the exclusion matters, which helps an agent choose correctly among alternatives.

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