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

Adds substantial context beyond annotations: the credit cost of each call, the three-valued meaning of "result" including the crucial caveat that "unknown" is neither valid nor invalid, and the warning that "success": true only means the request was processed. That last point is a non-obvious trap an agent would otherwise fall into.

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 what the tool does and its cost, then spends the second paragraph on output interpretation, which is genuinely necessary given there is no output schema. Every clause (including each named result field) carries distinct meaning; nothing is redundant.

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 takes on the full burden of explaining return values and does so field by field, including the ambiguous "unknown" case and the misleading "success" flag. An agent has everything needed to call the tool and interpret the response 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?

There is exactly one parameter and schema description coverage is 100%, so the schema already carries the meaning ("Email address to verify"). The description adds nothing about format, normalization, or constraints such as the 320-character limit, so the baseline 3 applies.

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 one email address") and enumerates the checks performed (syntax, domain, MX, mailbox, disposable, role, catch-all), which tells the agent exactly what the tool does. The word "one" implicitly distinguishes it from the plural sibling verify_emails without needing 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?

Gives clear operating context: single-address scope and "Consumes one credit", which lets an agent reason about cost versus the bulk siblings. It stops short of explicitly naming verify_emails as the alternative for multiple addresses, so the routing to siblings is implied rather than stated.

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