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

Annotations only say readOnly/openWorld; the description adds the behavioral layer that actually matters here: partial free results plus upsell links, Apify x402 payment path, Bearer tt_ token for full billed results, and three concrete rate-limit tiers (3/IP/UTC day, shared ASN pool 50, 300 global).

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 purpose, then usage exclusions, then pricing/auth, then quotas — a sensible priority order in short declarative sentences. Slightly dense in staccato fragments, and the x402 sentence is tangential to invocation decisions.

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 two-param read tool with no output schema, the description covers auth, cost, partial-result behavior, and quotas, which an agent needs before calling. It doesn't say which record types (A, MX, TXT) come back, leaving the return shape opaque, but nothing critical to correct invocation 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 already documents the domain/url alias and the anyOf requirement. The description adds only the 'one domain' constraint, which the schema property text already conveys.

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+resource: 'Returns DNS records for one domain.' The scope limitation ('one domain', 'not for batch work') cleanly separates it from neighboring domain_* tools that cover WHOIS, authority, or traffic data.

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 states when to use ('Use for one domain') and when not to ('Not for batch work or unrestricted monitoring'), but never names a sibling as the alternative for batch lookups, so the agent must infer the routing.

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