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

Annotations already declare readOnly, idempotent, open-world, non-destructive, so safety is covered. The description adds genuinely non-obvious behavior: recursive include:/redirect= expansion, counting DNS-querying mechanisms against the RFC 7208 limit of 10, and — critically — that each call costs $0.008 USDC via x402 on eip155:8453, which the annotations do not convey.

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 dense sentences with the capability and the flagged-problem list front-loaded and payment terms last. The only waste is the opening phrase repeating the title verbatim rather than adding a verb like 'Checks an SPF record by...', a minor redundancy.

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?

With no output schema, the description does the work of describing return content: include tree, lookup count vs the limit of 10, ip4/ip6 ranges, and the enumerated problem classes (multiple records, +all, ?all, missing includes, ptr, loops, void lookups). It is short only on failure modes — no-SPF-record or payment-failure behavior — which an agent would want to know.

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?

Only one parameter (domain) with 0% schema description coverage; the description implies the domain is the lookup target but never states format constraints (apex vs subdomain, no scheme/path) or the 300-char max. With a single obvious parameter the baseline of 3 is appropriate, though a clarifying clause would be cheap.

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?

Names a specific resource and verb ('SPF record check') and immediately enumerates the deliverables: full include tree, DNS lookup count, problems. An agent can tell this apart from dns_lookup, dns_dmarc, and email_security 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?

Usage is implied by the tool's specialization (SPF-only, RFC 7208 lookup counting), but there is no explicit when-to-use guidance, no mention of when to prefer dns_lookup or email_security instead, and no stated prerequisites such as the domain needing to exist.

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