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

Annotations provide readOnlyHint and openWorldHint, covering safety. The description adds behavioral context by listing the specific DNS record types returned, which is useful beyond the annotations. It does not mention error cases or resolver behavior, but this is acceptable given 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 highly concise: two sentences covering purpose and output, plus one line for the parameter. It is front-loaded and contains no fluff.

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?

Despite lacking an output schema, the description names the return record types, which is sufficient for a simple single-parameter tool. However, it does not describe response structure or failure modes, leaving a small gap.

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 input schema provides no description, but the description fully compensates with a clear definition and a concrete example for the single 'domain' parameter. This exceeds the baseline needed for undocumented schema parameters.

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 uses a specific verb 'Look up' and targeted resource 'DNS records for a domain', and enumerates record types (A, AAAA, MX, CNAME, TXT), making it clearly distinct from siblings like ip_geolocation or whois_lookup.

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 tool's purpose implies its usage scenario (DNS lookups), but there is no explicit guidance about when to choose it over alternatives, nor mention of exclusions. This is adequate but not explicit.

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