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

Annotations already cover read-only and open-world access, and the description adds genuinely non-obvious context: cost of $0.005 USDC per call on Base via x402 and, critically, that failed calls are not charged. It stops short of disclosing latency, rate limits, or whether the returned grade is cached.

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, zero filler: the capability list comes first and the pricing/charging policy second. Every clause carries information an agent needs.

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 compensates by enumerating the returned fields, and the payment model is disclosed. What is missing is any hint about response shape, size, or how partial failures (e.g. no RDAP for a ccTLD) surface in the result.

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 each parameter already carries a detailed description (including the ccTLD/RDAP caveat and the URL/email reduction rule). The description adds no parameter guidance beyond the word 'domain', so the baseline 3 applies.

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 the resource (domain) and enumerates exactly what is returned: DNS, MX, SPF/DMARC/DKIM grade, RDAP registrar/dates, hosting, tech stack, risk flags. No sibling tool (ad_creative_score, company_enrich, ai_visibility, serp_ai_monitor, read) overlaps, so the agent can route unambiguously.

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 enumerated data types — an agent infers this is the tool for domain-level inspection. But there is no explicit when-to-use framing, no statement of when not to use it, and no alternative named (the closest siblings, company_enrich and ai_visibility, are never referenced).

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