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

Annotations already cover the safety profile (read-only, idempotent, non-destructive, open-world). The description adds genuinely useful operational context beyond them: the 1-credit cost per call and the specific upstream resolvers used. It does not mention rate limits or failure/status semantics, so it stops 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 tightly-packed sentences: purpose front-loaded, then cost, then output shape. No filler; every clause carries information an agent needs before calling.

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 no output schema, the description compensates by spelling out the JSON return shape (name, type, status, records with value/ttl, count, resolver, elapsed_ms), plus cost and resolvers. Nothing essential is missing for this single-purpose lookup tool.

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 the schema already documents 'name', 'type', and 'all' (including punycode conversion and PTR address handling). The description only restates the record-type set and 'public name', adding little beyond the schema. Baseline 3 is correct.

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 (Look up), the resource (DNS records), enumerates all supported record types, and scopes it to public names resolved via Cloudflare and Google. An agent can distinguish this from ip_lookup and rdap_lookup immediately.

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 by 'public name' and the record-type list, but there is no explicit when-to-use guidance and no reference to the alternatives (e.g. rdap_lookup for registration data, ip_lookup for reverse lookups) despite those siblings existing. Adequate but leaves selection to inference.

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