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

Annotations declare readOnlyHint=false and openWorldHint=true, so a side effect is expected, but the description adds concrete substance: it consumes Reoon credits, requires an explicit confirm flag, and has a parallelism/rate constraint. It also discloses a limitation on the result's meaning (no inbox existence, no delivery guarantee). The one gap is idempotency/non-idempotency rationale and whether a failed or cached check still burns credits.

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?

Four short sentences, each carrying a distinct constraint: scope, limitation, cost/prerequisite, rate limit, and alternative routing. The capability statement is front-loaded and nothing is repeated from the annotations.

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 two-parameter tool with no output schema and no annotations explaining results, the description covers cost, gating, limits, and what is not verified. It stops short of indicating the shape or meaning of a returned verdict (e.g., status vs. sub-signal breakdown), which an agent would need to interpret results without probing.

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 0%, so the description must carry the load, and it does for the non-obvious parameter by stating 'confirm:true is required' — without this the boolean would default to false and the call would silently not do what the agent intends. The email parameter is largely self-documenting via format/pattern/maxLength in the schema, so only minor value is missing.

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 ('Check email syntax, domain/MX and disposable-address signals') and scopes it to QUICK mode, which separates it from the bulk siblings named in the context. It also explicitly bounds the claim ('Does NOT verify inbox existence'), so an agent knows exactly what class of check this is.

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?

Explicit routing is given: 'Use bulk verification for lists' names the alternative and the condition that selects it (reoon_create_bulk_verification). It adds both a prerequisite ('confirm:true is required') and an operational exclusion ('Do not run continuously in more than five parallel requests').

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