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

With no annotations, the description carries the full burden and does well: it discloses the data source (crt.sh), the passive nature ('without touching the target'), deduplication, and the $0.02 x402 USDC pricing on eip155:8453. It omits rate limits, failure modes when crt.sh is unavailable, and whether results are capped/sorted by the limit parameter.

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?

The purpose sentence is well front-loaded, but the follow-up 'Use this when an agent needs to subdomains disclosed by public CT logs (crt.sh)' redundantly repeats the first sentence and contains a grammatical error, and the pricing detail interrupts the flow.

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 2-param, no-annotation, no-output-schema tool, the description covers the source, the return concept (deduplicated subdomain list from historical certs), passivity, and cost. Missing only result ordering/truncation behavior and error conditions.

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%, so baseline is 3. The description adds only the 'deduplicated' qualifier and the notion of enumerating all historical certificates; it says nothing about how `limit` truncates results or what `domain` accepts (apex vs. URL).

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 (enumerate) and resource (subdomains from Certificate Transparency logs via crt.sh), plus scope ('every TLS certificate ever issued for the domain or its subdomains, deduplicated'). This clearly distinguishes it from sibling recon tools such as live_dns_lookup and security_ssl_inspector.

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 sentence 'Use this when an agent needs to subdomains disclosed by public CT logs' gestures at when-to-use but is grammatically broken and effectively restates the purpose. No explicit exclusions or named alternatives (e.g., DNS enumeration vs. CT logs) are given, leaving usage guidance only implied.

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