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

Annotations already carry the safety profile (readOnlyHint=true, openWorldHint=true, destructiveHint=false). The description adds value by enumerating the facts returned, helping an agent understand what this read operation produces. It aligns with the annotations and adds coverage context; it doesn't mention network latency or rate limits, but for a simple read tool with annotations present this is adequate.

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?

One dense sentence, front-loaded with the core purpose before a colon-delimited fact list. Every item in the enumeration earns its place and there is no filler, though the list runs long.

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?

The tool is low-complexity: a single required parameter, no output schema, and no nested objects. Annotations cover the read-only safety profile, and the fact list gives a strong sense of the return coverage. Given the low complexity, nothing critical is missing for an agent to call this correctly.

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 single 'domain' parameter is fully documented with an example in the schema. The description adds no format details beyond what the schema already provides, so the baseline of 3 applies. No additional parameter semantics are needed here.

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 (check) and resource (DNS and hosting facts) with a detailed enumeration of coverage: nameservers with provider, A/AAAA with ASN owner, CNAME, MX, CAA, SPF/DMARC, DNSSEC, registrar, and RDAP expiry. This differentiates it from siblings like check_certificate and check_dns_propagation. However, it doesn't explicitly separate itself from check_expiry, which also reports expiry, leaving minor ambiguity.

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 offers no guidance on when to use this tool versus its alternatives. check_dns_propagation (propagation status) and check_expiry (expiry only) overlap meaningfully with this tool's fact set, yet no exclusions or alternative routing is provided. An agent must infer usage from the fact list alone.

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