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

Annotations already declare readOnly, idempotent, open-world, non-destructive, so the safety profile is covered. The description adds that resolution goes 'through a public resolver', which hints at caching/geo-dependency and no local zone or custom-server support, but it does not mention failure modes (NXDOMAIN, resolver timeouts, result caching).

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?

A single front-loaded sentence with no filler; the record-type parenthetical is useful but slightly redundant with the enum. Nothing is buried 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?

For a simple read-only, two-parameter tool with full schema coverage and rich annotations, the description gives enough to invoke it correctly. Only return-shape expectations (answer records, TTLs, NXDOMAIN handling) are left implicit, and there is no output schema to cover them.

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%; the schema already documents the type enum and the domain normalization behavior (URL/email reduced to domain). The description's record-type list merely echoes the enum and adds no syntax, default, or edge-case detail beyond the schema, so baseline 3 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 ('Looks up') and resource ('DNS records'), names all supported record types, and specifies the resolution path ('through a public resolver'). It does not distinguish itself from siblings like dig, dns_propagation, or dns_trace, which is the only thing keeping it from a 5.

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?

There is no when-to-use or when-not-to-use guidance and no alternative is named, even though the sibling set contains several overlapping DNS tools (dig, dns_propagation, dns_trace, reverse_dns). The agent must infer selection criteria entirely on its own.

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