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

Annotations cover the safety profile (readOnlyHint, idempotentHint, openWorldHint, destructiveHint=false), and the description goes well beyond them: live querying against named public resolvers (Cloudflare, Google, Quad9), the exact email grading rules (SPF ending in -all/~all, DMARC p=quarantine/reject), pricing (free), and error semantics (isError with a message, not charged). This is exactly the behavioral context an agent needs.

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 core capability, then cleanly delimited sections for resolvers, grading, usage, price, and errors. Dense but every clause carries information; no filler.

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 shape needn't be described, and the description otherwise fully equips an agent: what it returns, how email is graded, where it queries, what it costs, and how failures manifest. Nothing needed 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?

With a single parameter at 100% schema coverage, the schema already documents the 'domain without scheme' format. The description adds no parameter-level syntax or constraints beyond what the schema provides, so the baseline 3 is appropriate.

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+resource (lookup all DNS records for a domain) and enumerates the record types returned, plus the extra value-add (SPF/DMARC graded). It explicitly distinguishes itself from siblings by naming domain_whois and tls_check, so an agent can route correctly without opening any schema.

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?

Provides an explicit 'When to use' clause plus concrete alternatives with their selecting conditions: domain_whois for ownership dates, tls_check for certificates. Both the positive case and the exclusion boundaries are stated.

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