Check email for disposable

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

Annotations include readOnlyHint=true and openWorldHint=true, but the description goes much further by disclosing the fail-open behavior: on network problems, timeouts, rate limits, or server errors, the tool still succeeds with `checked:false` and `action:allow`, and this must be treated as inconclusive. It also details optional response fields (`mx_valid`, `relay`, etc.), which is valuable context not present in the annotations.

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?

The description is long, but it is well-structured and front-loaded with the core action. It then explains the disposable concept, response fields, and failure mode—each element adds value, especially given there is no output schema. It is slightly verbose but not redundant; every sentence serves a purpose.

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 a single parameter and no output schema, the description fully equips an agent to invoke the tool and interpret results. It covers input, all relevant output fields, the meaning of the verdict, and the critical fail-open behavior that could otherwise mislead the agent. The description is complete for the tool's complexity.

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% for the single `email` parameter, which already includes a clear example ('someone@example.com'). The description repeats that example but adds no new technical constraints or formatting rules. It focuses on the semantic meaning of 'disposable,' which is helpful for concept understanding but does not deepen parameter semantics beyond the baseline.

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?

The description opens with a clear verb+resource: 'Checks a single email address to see whether it is disposable.' This specifically distinguishes it from sibling check_batch (which would handle multiple addresses) and check_domain (which targets domains), and the scope is immediately evident.

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?

It explicitly scopes the tool to 'a single email address,' which implies that batch checks should use the check_batch sibling. While it does not name alternatives or exclusion criteria, the clear single-address context provides sufficient guidance for selecting between the listed sibling tools.

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