dns_lookup

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

Description goes beyond annotations by disclosing rate limits (30/hr Free, 500/hr Pro) and detailing TXT record handling (raw unfiltered, honest total count). No contradictions with annotations (readOnlyHint, idempotentHint). Adds valuable behavioral context.

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?

Description is concise: three sentences front-load purpose, then usage, then behavioral specifics. Every sentence adds value, no fluff. Structurally efficient.

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's simplicity (1 param, high schema coverage, annotations present, output schema exists), the description covers all necessary aspects: purpose, usage, behavioral traits (rate limits, TXT handling), and return structure. Complete for the tool's complexity.

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?

Only one parameter with 100% schema coverage. Description reinforces domain format (e.g., 'example.com') and adds clarity on acceptable input. While schema already documents it, the description adds practical guidance without being redundant.

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 queries all DNS record types for a domain, lists specific record types (A, AAAA, MX, etc.), and provides specific use cases like mail routing inspection and nameserver verification. It also distinguishes itself from the sibling tool domain_report, clarifying scope.

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?

Explicitly states when to use this tool ('for mail routing inspection, nameserver verification, or SPF/DMARC checks') and when to use alternative (domain_report for full overview or security-only TXT view). This provides clear context for selection.

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