dns_lookup

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

With no annotations, the description carries the full burden. It discloses that it uses the system resolver, default lookup coverage, reverse PTR for A results, and explicitly notes 'No SSRF risk — DNS only, no outbound connections.' This significantly clarifies behavior and safety, though it omits response format or error handling.

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?

Three sentences, front-loaded with the core purpose, followed by default behavior, use cases, and safety. No wasted words; every sentence contributes necessary information.

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 tool with no annotations and no output schema, it covers purpose, defaults, reverse PTR behavior, use cases, and safety. It could be more complete by mentioning return format or failure semantics, but the core selection and invocation needs are met.

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 only 50% (domain is described, types is not). The description adds some context by listing default record types and implying the types parameter can override them, but it doesn't explicitly explain the parameter's role or format. The domain parameter's schema description already covers hostname-not-URL guidance, so the description adds marginal value beyond that.

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 clearly states the tool resolves DNS records for a domain, with a specific verb and resource. It enumerates default record types (A, AAAA, MX, TXT, NS, CNAME, SOA, CAA) and adds the reverse PTR behavior, making it highly distinct from sibling tools like ssl_check or url_metadata.

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?

Provides explicit use cases: 'debug mail config (MX), domain ownership signals (TXT), name-server delegation (NS), CAA policy, and IP resolution.' This gives clear context for when to use the tool. No exclusions or alternative tool mentions, but given the uniqueness of DNS lookup among siblings, this is sufficient.

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