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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds genuinely new behavioral context: the 50-address batch ceiling and, importantly, that each address consumes 1 credit — a billing trait the annotations do not convey for an otherwise read-only-labeled tool.

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?

Two short, front-loaded sentences with zero filler. The action and its hard limit come first, followed immediately by the cost implication.

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?

There is no output schema, so the description should ideally hint at what verification results look like (e.g., per-address validity status and how they map to the input order). Cost and limits are covered, but return-shape information is entirely absent for a tool with no output schema.

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% for 2 parameters, so the description must compensate. It clarifies that 'emails' is a batch with a maximum of 50 entries, but the api_key parameter is never addressed and no format guidance (e.g., array vs delimited string) is given beyond the schema's array type.

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 with scope ('Bulk-verify up to 50 emails'), which implicitly contrasts with the singular sibling verify_email. The 'Bulk' qualifier and the 50-address cap make the tool's role easy to distinguish from verify_email, though it never names the sibling explicitly.

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 implies when to use it (when you have many addresses to check) via 'Bulk-verify up to 50 emails', and the cost line helps an agent judge whether to invoke it. However, it never explicitly routes the agent between this tool and verify_email, nor states prerequisites beyond the credit cost.

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