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

Annotations already declare read-only, idempotent, non-destructive, open-world behavior, so the bar is lower. The description adds substantive behavioral context beyond that: no SMTP probe limitation, per-call cost (0.02 USDC), p95 latency (2500 ms), and the 20-address batch cap.

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?

Front-loads the usage condition and exclusion before the return-value details; every sentence (use case, exclusions, return contents, cost/latency) carries distinct information with no filler.

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 an output schema present the description need not enumerate return fields, yet it still summarizes the verdict structure and counts. Combined with rich annotations and full parameter coverage, an agent has everything needed to invoke 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%, so both parameters (emails and response_format) are already documented in the schema, establishing a baseline of 3. The description reiterates the 20-address cap but adds no syntax, format, or breaking-down detail beyond what the schema states.

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 (bulk email validation / email list verification) and explicitly distinguishes itself from the sibling blackwood_email_check by rejecting single-address use. An agent can identify the tool's domain 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?

Explicitly names when to use it ('before a send or import'), when not to use it ('one address', 'proving a mailbox exists', 'sending email'), and points to the cheaper alternative email-check. Nothing is left to inference.

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