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

Annotations already declare read-only, idempotent, open-world, and non-destructive behavior. The description adds useful context beyond annotations by stating 'No login required' and emphasizing that lookups work on any domain, not just owned domains. It does not mention rate limits, caching, or failure behavior, but the core behavioral profile is well covered.

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 front-loaded with the purpose and supported record types, then gives return shape and usage context. It is efficient overall, though the record types are listed twice—once as supported lookups and again in the returned object—which is slightly 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?

For a simple read-only lookup with one required parameter and rich annotations, the description covers purpose, scope, use cases, authentication ('No login required'), and return shape. No output schema exists, but the description supplies the expected response structure, so an agent has enough to call it 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?

Schema description coverage is 100%, so the single 'domain' parameter is already documented with an example. The description reinforces that any domain is acceptable, but it does not add format, normalization, or validation details beyond the schema.

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 states a specific verb and resource ('Look up DNS records') and enumerates the supported record types (A, AAAA, MX, TXT, NS, CNAME). It also distinguishes scope by saying it works for 'any domain (not just domains they own)', which helps separate it from tools like get_dns_records that likely operate on owned domains.

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 gives clear use cases: customer questions about DNS configuration, nameservers, mail routing, or verifying a specific record. It also clarifies the any-domain/not-owned condition. However, it does not explicitly name an alternative sibling tool or state when not to use this tool.

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