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

Goes well beyond the readOnly/idempotent annotations: discloses the x402 payment mechanism and $0.04 USDC cost, that payment goes in _meta["x402/payment"], that partial failures still return partial results, and that invalid input or total failure is not charged. These are exactly the operational facts an agent needs before spending money on a call.

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?

Single dense paragraph that front-loads what the tool returns and when it applies, then appends failure and payment terms. Every clause carries distinct information — output fields, sources, partial-failure semantics, cost, non-charging conditions — with no filler.

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 and no output annotations, the description fully compensates by naming each returned field and the aggregate result. It also covers the failure modes and billing implications of a paid, open-world network operation, leaving nothing an agent must guess before invoking it.

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 100% and the single parameter already documents the '2 to 5 comma-separated domains' format. The description restates the cardinality but adds no new syntax or edge-case guidance (e.g. duplicate handling, whitespace, max URL length) beyond the schema.

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 (certificate and domain-registration expiry lookups) with explicit scope (2 to 5 domains in one call) and enumerates exactly what comes back: days left, expiry dates, ok/warn/expired status, soonest date overall. The batch scope plus the data sources (CT logs, RDAP) distinguish it clearly from single-target siblings like check_cert and check_domain_expiry.

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?

The 2-to-5 domain batch constraint makes the intended use case obvious against the single-domain siblings, and the partial-failure/all-fail behavior tells the agent what to expect on mixed input. It never names an alternative tool explicitly, so selection against check_cert or check_domain_expiry is inferred rather than stated.

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