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

With no annotations, the description carries the full burden of behavioral disclosure. It only mentions 'format + DNS check' but does not explain what happens on failure (e.g., returns false vs throws), whether it performs live network calls, or what the output structure is. This is minimal transparency.

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 extremely concise, using only four words. It is front-loaded with the key action and resource. While it could benefit from a bit more structure, it earns a high score for not wasting words.

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?

Given the tool has no annotations and no output schema, the description should explain what the tool returns or how to interpret results. 'Domain format + DNS check' is incomplete for an agent to know whether the tool returns a boolean, a reason for failure, or DNS details. It also lacks context on when to use it versus similar validators.

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 parameter 'domain' described as 'Domain name'. The description adds no additional semantics beyond the schema, but given the parameter is simple and self-explanatory, baseline 3 is appropriate.

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 'Domain format + DNS check' clearly states the tool's function: it validates domain format and performs a DNS check. This distinguishes it from sibling validators like validate_url or validate_email, and from dns_lookup which is a lookup rather than a validation.

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 provides no guidance on when to use this tool versus alternatives. It does not mention that this is for checking if a domain is well-formed and has DNS records, versus a full URL validation or a raw DNS lookup. No explicit when/when-not context is given.

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