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

Annotations already establish read-only/idempotent/non-destructive, but the description goes well beyond them: per-call cost of $0.03 USDC via x402 with the payment location (_meta["x402/payment"]), the partial=true degradation when one or two sources fail, and the billing rule that errors are not charged. That is exactly the operational context an agent needs before invoking a paid tool.

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?

Purpose is front-loaded and routing guidance follows immediately; nearly every clause carries usable information. The first sentence, however, is a dense run-on that bundles return contents, a dated flag and a certificate note, which slightly muddies scanning.

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 still tells the agent what the response contains (raw sub-results, summary, renewal-stall flag, LE 64-day note) and how failures surface (partial=true). Combined with the pricing and error-billing rules, nothing needed to call or interpret this tool is missing.

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 exists and the schema already documents it at 100% coverage, including accepted hostname/URL formats, so the baseline is 3. The description adds nothing about the domain argument itself (no normalization, no example beyond the schema's own), so it neither compensates nor regresses.

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 concrete composite action — running check_cert, check_dns and check_domain_expiry together — and enumerates what comes back (raw results, summary, renewal-stall flag, 64-day cert note). It also explicitly distinguishes itself from the sibling domain_grade, so an agent can route without opening schemas.

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?

Gives an explicit when-to-use ('a full data dump in one call') and a named alternative with the condition that selects it ('use domain_grade if you want a single scored A-F answer that also covers email auth and HTTP headers'). It further explains the partial-failure path, which removes ambiguity about degraded runs.

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