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

Goes far beyond the readOnlyHint and openWorldHint annotations by disclosing the exact execution model (six parallel Cloudflare DoH queries, 5 s timeout each) and the complete status return contract (ok, not_applicable, timeout, error) with guidance on interpretation. This is rich behavioral context that annotations alone do not provide.

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?

The description is a single paragraph but every sentence earns its place: purpose, usage routing, execution details, return format, and interpretation guidance. It is front-loaded with the primary action and efficiently organized, with no filler or redundancy.

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 multi-record-type tool with no output schema, the description fully covers the return contract and error semantics, including how to treat each status. It also provides sufficient operational context (timeouts, parallelism) and routing to alternatives. Nothing an agent needs to call it correctly is missing.

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 100% and the schema description for 'domain' is thorough (public domain name, rejects IPs/ports/paths). The tool description does not add parameter-specific semantics beyond restating the resource scope. With full schema coverage, a baseline of 3 is appropriate; no extra value is added by the description.

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 states a specific verb ('fetch'), a precise resource (domain's A, AAAA, NS, SOA, CAA and TXT records), and enumerates the record types. It clearly distinguishes itself from dns_lookup by naming the alternative and its use case, so an agent can select it unambiguously.

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?

Explicitly instructs when to use this tool ('first step of a DNS review') and when to prefer an alternative ('prefer dns_lookup for a single record type or for MX, CNAME and SRV'). This leaves no ambiguity about selection criteria and names the sibling explicitly.

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