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

With no annotations provided, the description carries the full burden and does disclose meaningful behavioral details: live network checks via DNS-over-HTTPS, pricing per call, the free demo mode, and the 2KB input cap. However, it does not disclose the response format, possible error behavior, or how authentication works beyond mentioning a 'credits key.'

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 two compact sentences with all information front-loaded. The first sentence states purpose and scope; the second covers request format, pricing, and demo limitations. No sentence is wasted.

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?

For a simple read-type verification tool with no annotations and no output schema, the description covers purpose, input mechanics, and cost constraints well. However, it never explains what the tool returns after checking, which is a notable gap given no output schema exists to fill in that information.

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?

The schema only describes 'email' as a single address and 'emails' as an array with maxItems 20. The description adds significant semantics by specifying the POST body format, that the two parameters are alternatives, the maximum batch size, and the 2KB input cap, compensating for the 50% schema coverage.

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 the specific verb 'Check' and clearly identifies the resource (an email address) and the specific checks performed: RFC syntax, live MX records via DNS-over-HTTPS, and disposable-domain screening. This distinguishes it from all sibling tools, which are unrelated conversion/scheduling utilities.

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 gives concrete calling patterns (POST either { email } or { emails: [...] }) and constraints, making the intended usage immediately clear. It does not explicitly mention alternative tools or when-not-to-use, but none of the sibling tools overlap in purpose, so the lack of exclusions is acceptable.

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