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

Annotations already declare readOnly, idempotent, openWorld, non-destructive, so the safety bar is covered. The description adds real behavioral substance: power mode performs a live SMTP handshake, yields a catch-all flag and 0-100 score, while quick trades certainty for cost/speed.

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?

Three tight sentences, front-loaded with the core action, followed by mode semantics and a concrete example. The example is slightly redundant with the schema example but does not bloat the definition.

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 usefully signals what power mode returns (explicit catch-all flag, 0-100 score). It stops short of describing the full response shape or error behavior, but covers what an agent needs to choose a mode and call the tool.

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 mode enum is already fully documented in the schema, so the description mostly restates it. It does add consequence-level framing (catch-all flag, 0-100 score, less certain), which is marginal value beyond the structured field, landing at baseline.

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 (Verify) and resource (a single email address) plus the provider (Reoon), which is unambiguous and distinguishable from siblings like validate_claim or company_facts that concern other data.

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?

Explains the choice between power (default, SMTP handshake, catch-all + score) and quick (faster, cheaper, less certain), giving clear context for mode selection. It does not, however, state when to reach for this tool over other verification-adjacent siblings.

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