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

Goes well past the readOnlyHint/openWorldHint annotations: discloses the hard 15-variant cap, the explicit IDN/Unicode coverage gap, the interpretation caveat that a hit is not a verdict, and a full pricing contract ($0.002 USDC per successful call via x402 on Base/Solana/Arc, failures free). Those are exactly the traits an agent needs before deciding to spend.

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?

One dense paragraph, front-loaded with what it builds, then the semantics caveat, then the coverage limitation, then cost. Every clause carries distinct information and nothing is repeated from the schema.

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 shape needn't be described, and cost, limits and interpretation are all covered. Minor gap: the description never hints at result ordering or whether every variant is echoed back, but the output schema plausibly handles that.

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 both the description and schema give the same paypal.com example plus the URL-to-host normalization rule, so the description adds little beyond the schema. Baseline 3 is appropriate when the parameter is fully documented in structured data.

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 and resource: builds up to 15 enumerated look-alike variants of a brand domain and checks which are registered via RDAP. The mutation taxonomy (omission, doubling, swaps, 0/1 homoglyphs, hyphens, login prefixes, other TLDs) makes it unmistakable against siblings like domain_authority_credibility or subdomain_takeover_monitor.

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?

Explains the use case (brand-domain impersonation reconnaissance) and pre-empts the main misinterpretation with 'Registered means taken, not malicious: each one needs a content check', which routes the agent to a follow-up verification step. It does not, however, name alternative siblings (e.g. known_scams_blacklist_db) or state when a different tool is the better choice.

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