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

Annotations already cover readOnly/idempotent/destructive and open-world, so the baseline is low; the description adds genuinely new behavior: a hard 50-address ceiling, deduplication ('duplicates are checked once'), and the response shape (counts plus per-address results). No contradiction with idempotentHint — dedup is consistent with idempotency.

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 short sentences, front-loaded with the capability and limit, then the use case, then the overflow rule. Every sentence carries information that is not in the schema or 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?

An output schema exists, so return values need only light mention, and the limit/splitting/dedup guidance covers the operational gaps. The only missing piece for full call correctness is an explicit pointer to verify_email for single addresses.

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 array bounds are already in the schema, so baseline is 3. The description earns above baseline by disclosing array-handling semantics the schema cannot express: duplicates are deduplicated rather than re-verified, and oversize lists must be chunked by the caller.

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 email addresses) plus the batch scope ('up to 50 in one call'), which implicitly separates it from the single-address sibling. It never names verify_email explicitly, so the distinction is inferred from scale rather than declared.

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?

Gives a concrete use case ('a lead list before an outreach campaign') and a clear guiding rule for oversized inputs ('For larger lists, split into several calls'). It omits the more important routing cue: that a single address should go to verify_email instead.

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