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

With no annotations, the description carries the full burden and does disclose two non-obvious traits: it is a paid operation ('$0.003 USDC per call via x402') and it returns per-check status, issues, recommendations, a 0-100 score and A-F grade. 'Audit'/'check' implies read-only, but it never explicitly confirms no side effects, nor does it mention rate limits, lookup timeouts, or whether failed DNS lookups surface as errors.

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?

Two sentences, both front-loaded: the first defines the audit scope, the second covers output and cost. The dense parenthetical enumerations are informative rather than filler, so every clause earns its place.

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-parameter, read-only audit tool with no output schema and no annotations, the description covers scope, return shape, and payment requirement well. What is missing is an explicit statement of read-only safety and any error/edge behavior (e.g., domains with no records), which matters given the absence of annotations.

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% and both parameters are self-documenting, so the schema already does the heavy lifting. The description's '(common or given selectors)' and 'key type and length' add only marginal meaning over the selectors default list already present in the schema, so 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 (audit) and resource (a domain's email authentication DNS) and then enumerates exactly what is inspected: SPF qualifier/lookups, DMARC policy fields, DKIM selectors, MX, BIMI/MTA-STS/TLS-RPT. An agent can tell this apart from a generic 'health' sibling purely from the description, since the enumerated DNS records make the scope unmistakable.

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 the domain-audit framing, but the description never states when to reach for this versus alternatives (e.g., the 'health' sibling) or any prerequisites such as needing a resolvable, owned domain. No explicit when-to-use or when-not-to-use guidance is provided.

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