dns_lookup

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

With no annotations, the description carries the burden and does well: it discloses that the lookup is passive and the target's own servers are not contacted, plus cost (1 quota unit) and typical latency (under a second). These are exactly the behavioral facts an agent needs for planning. It does not discuss failure modes or output shape, keeping it short of a 5.

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 short sentences, front-loaded with what the tool does, followed by scope exclusions and cost. Every clause earns its place; nothing is repeated or padded.

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?

An output schema exists, so return-value explanation is unnecessary, and the description covers the remaining gaps: passivity, excluded operations, cost, and latency. For a two-parameter read-only lookup, an agent has everything needed to select and invoke 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% and both parameters (host, record_types) are documented in the schema, including a default. The description's parenthetical record-type list restates what the schema already conveys and adds no format or syntax detail, so the baseline 3 for high coverage applies.

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?

States a specific verb and resource ('Look up DNS records') and enumerates the record types covered, scoped to 'a domain in scope'. This cleanly separates it from sibling tools like whois_lookup, certificate_transparency, and tls_certificate_info without requiring the agent to open the schema.

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?

Gives explicit when-not guidance: 'Does NOT do subdomain enumeration or zone transfers', which prevents misuse by an agent looking for enumeration. It also notes the operation is passive. It stops short of naming a sibling alternative for those excluded tasks, so it is strong but not exhaustive routing guidance.

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