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

With no annotations, the description carries the full behavioral burden and largely succeeds: it discloses the transport (DNS-over-HTTPS), result ordering semantics (primary/lowest priority first), data freshness ('live from DNS'), and a non-obvious cost/payment mechanism ('x402 price $0.02/call (USDC, eip155:8453)'). It does not cover edge behavior such as a domain with no MX records or implicit A-record fallback.

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 action and return shape, which is good. However, 'Use this when an agent needs to mail exchangers by priority, live from DNS' largely restates the opening clause, and the trailing pricing aside is useful but wedged on abruptly.

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 single-parameter, no-annotation, no-output-schema tool the description supplies the key context an agent needs: what is returned, how it's ordered, that it's live, and that it costs money. The only real gap is failure/empty-result behavior, which is not addressed.

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 reported at 100% but the sole schema description is the useless string 'Domain', so the schema isn't actually carrying meaningful semantics. The description only adds 'for any domain', which is marginal. Baseline 3 applies when the schema nominally covers the single parameter.

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: 'Query the MX records for any domain via DNS-over-HTTPS', and specifies the returned shape ('every mail exchanger with its priority, sorted so the primary comes first'). It is precise about what MX is, but it never distinguishes itself from the closely related sibling live_dns_lookup, which an agent would reasonably see as overlapping.

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?

Gives a concrete use case: 'The definitive check for "can this domain receive email" before sending anything. Use this when an agent needs mail exchangers by priority.' That is clear context for when to reach for it, but no exclusions or explicit alternative (e.g., live_dns_lookup) are named.

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