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

Annotations already establish read-only, idempotent, open-world, non-destructive behavior, so the bar is lower. The description nonetheless adds real context: queries are live, they go through Cloudflare's public resolver, and responses include TTLs plus an explanatory page.

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?

Two dense sentences, front-loaded with what the tool does before enumerating types and return details. Informative without padding, though the type enumeration is slightly list-heavy.

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?

With an output schema present the description need not explain return values, and it covers the resolver, live behavior, record types, and reverse lookups. Mildly thin on pagination/limits for a forward lookup that can return many records, but otherwise 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% and the enum enumerates the types, so the schema carries the load. The description reaffirms record types and the reverse-DNS/PTR case but adds no syntax or format detail 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?

States a specific verb+resource ('Look up the DNS records of any domain or hostname') and adds scope (live, via Cloudflare's public resolver, including reverse PTR). It does not explicitly distinguish itself from whois_lookup or check_name, so it stops short of the 5 given the sibling set.

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?

Usage is implied rather than stated: the reader infers this is the tool for DNS queries and that PTR is used for IPs. There is no explicit when-to-use/when-not or routing to whois_lookup for registration data, so it is minimum-viable guidance.

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