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

Annotations only say readOnly and openWorld; the description adds materially important behavior: a $0.002 USDC charge per successful call via x402 on Base/Solana/Arc, and that failed calls are not charged. That payment/failure policy is exactly the kind of context annotations cannot convey. It stops short of describing latency, rate limits, or response shape.

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 what is returned and how it is paid for, which is good. However, the parenthetical justification of missing data ('Tranco rank API needs a key; DNS-over-HTTPS was unreachable from the test network') is internal-sounding filler that does not help the agent decide or invoke.

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 values need not be explained, and the description covers the source, the capability boundary, and the payment model. With one simple string parameter, an agent has enough to call it correctly; only the absence of explicit sibling routing keeps it from a 5.

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?

One parameter with 100% schema description coverage, including the useful note that a full URL is accepted and reduced to its host. The description adds nothing about the domain parameter, so the baseline 3 applies since the schema carries the semantics.

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 source (registration facts from the public RDAP directory) and enumerates the returned fields (registration date, age, expiry, registrar, lock status). It also actively corrects the misleading tool name by stating there is no authority score, backlink or spam index, which distinguishes it from what an agent might infer from 'authority_credibility'. It does not, however, name any sibling tool it competes with.

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 only implied — an agent can infer this is for domain age/registration checks, and the description tells it when the tool will NOT answer (no authority, backlink or spam data). But no explicit when-to-use condition or named alternative (e.g. DNSSEC validator, typosquat radar) is given.

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