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

With no annotations provided, description carries the burden. It discloses live query behavior and the NXDOMAIN vs no-record distinction, which is valuable context. It doesn't cover error handling or return format, but the tool is read-only and the key behavioral nuances are addressed.

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: purpose, usage context, behavioral distinction. Each sentence serves a distinct role, no redundant wording, and the most important info is front-loaded.

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 DNS lookup tool with full schema coverage and no output schema, the description covers purpose, when to use, and a key behavioral distinction. It doesn't describe the output shape, but the core usage and behavior are sufficiently complete.

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 baseline is 3. The description lists record types but omits the COMMON option and its aggregate behavior, which the schema covers. No additional semantic value added 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 uses specific verb 'look up' with resource 'live DNS records' and lists all supported record types. It clearly distinguishes this tool from siblings by focusing on DNS state, while other tools handle email auth, security headers, service status, etc.

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?

Explicit 'Use whenever the real, current DNS state matters' followed by concrete scenarios (domain pointing, mail servers, resolution, propagation). It doesn't explicitly name alternatives or when-not-to-use, but the guidance is clear enough for correct tool selection.

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