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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds real value beyond them: per-call pricing ($0.008 USDC via x402), the upstream dependency (crt.sh), and that results are unique and capped. However, 'capped' is not quantified and no latency, rate-limit, or upstream-failure behavior is disclosed.

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?

Three sentences, front-loaded with what the tool does, followed by result shape and cost. The x402 pricing and HTTPS fallback both earn their place for an agent deciding whether to call; only the raw endpoint URL is slightly incidental.

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?

For a simple one-parameter read-only tool with no output schema, the description covers mechanism, return shape ('unique hostnames, capped'), and cost. Remaining gaps are the cap value, domain formatting rules, and error/payment-failure behavior, which are moderate rather than fatal.

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?

There is one required parameter with 0% schema description coverage, so the description must carry the burden and only partially does: 'issued under the domain' implies a bare registrable domain rather than a URL or wildcard, but format expectations, subdomain handling, and validation behavior are never stated.

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 verb (subdomain enumeration via Certificate Transparency), the concrete data source (crt.sh JSON API), and the return payload (unique hostnames under the domain). An agent can distinguish this from generic DNS or domain-intel siblings because the CT/crt.sh mechanism is explicit.

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: the tool is for finding subdomains through certificate issuance records. There is no statement of when to prefer this over siblings like dns_dump or domain_intel, nor any exclusion or precondition (e.g. only covers hosts with TLS certs). The alternate HTTPS endpoint is provided, but that is an access path, not selection guidance.

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