dns_lookup

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

With no annotations, the description carries the full behavioral burden and does well: it discloses that TTLs are returned, that the CNAME chain is followed (extra queries/records beyond the literal name), and that NXDOMAIN and NODATA are reported as distinct outcomes. It omits any note on timeouts, retries, or whether lookups are cached, which keeps it from 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?

Front-loaded with the capability sentence, then one paragraph per non-obvious parameter, with zero filler or repetition. Every clause earns its place — the type list and resolver list exist precisely because the schema declares no enums.

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 values need not be explained, yet the description still adds the key result discriminator (NXDOMAIN vs NODATA), which is genuinely useful. Minor gaps remain: no mention of name syntax edge cases (trailing dot, wildcards) or failure behavior if a custom resolver IP is unreachable.

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 coverage is 0%, so the description must compensate, and it does: `types` gets the full valid value list plus comma-separated syntax, and `resolver` gets every accepted value ('system', 'cloudflare', 'google', 'quad9', or a literal IP with optional port). Only the required `name` parameter is left uncharacterized, though its meaning is self-evident.

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?

Opens with a specific verb and resource: 'Look up DNS records with TTLs, following the CNAME chain.' The scope (TTL reporting, CNAME chain traversal) is concrete. It does not differentiate itself from the closest sibling, email_dns_check, so it stops short of 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?

The description supplies one real use case — choosing a non-system resolver 'is how you compare what different resolvers see' — which implies when the parameter matters. However, there is no explicit when-to-use-this-vs-alternative guidance, and email_dns_check (the obvious overlap) is never mentioned or excluded.

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