verify_email

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

With no annotations, the description carries the full behavioral burden and does add real value: it discloses that the tool never fabricates a 'valid' result and that 'unknown' is a genuine outcome with concrete causes (security gateway, uncooperative mail server). It omits operational traits such as latency, cost, or rate limits, which matter for a live SMTP-style check.

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?

Purpose is front-loaded in the first clause and the elaboration follows. The sentence is somewhat long and the parenthetical explanation of 'unknown' borders on redundant with the preceding clause, but every element is relevant.

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 simple one-parameter lookup with no output schema, the description appropriately explains the meaning of the returned statuses, which is exactly what the missing output schema would otherwise carry. It leaves out operational details like cost or speed, but nothing needed to call it correctly is absent.

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?

There is a single parameter with 100% schema description coverage, including an example format, so the schema does the work. The description adds no format or syntax detail beyond it, so the baseline of 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 and resource: 'Verify whether an email address is deliverable using Kluno.' An agent immediately knows the operation and the outcome types (valid / invalid / catch-all / unknown) without opening the schema.

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 context for interpreting results (what 'unknown' means, why it is honest) but never states when to call this tool, e.g. before a send or list-import, nor any preconditions. Usage is implied rather than directed, and there are no sibling tools to route against.

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