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

Goes well beyond the readOnly/idempotent/openWorld annotations: it discloses deduplication, the returned attributes (wildcard flag, first-seen, expiry, issuer), primary source crt.sh with Cert Spotter fallback, and that the response names the source. It also documents the paid x402 USDC flow and the PaymentRequired object, which is critical invocation behavior.

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?

Front-loads the use case, then the data scope, then sourcing, then the payment model, in a compact sequence. Every clause carries distinct information (return fields, fallback source, pricing, PaymentRequired behavior) 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, the description compensates by enumerating the returned fields and provenance. Combined with the payment/unauthenticated-call path and the explicit data-source limitation, an agent has everything needed to call this correctly.

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 both `domain` and `limit` are already documented in the schema with acceptable format guidance ('example.com', 1-5000). The description adds no input-syntax detail beyond the schema, so the baseline 3 applies.

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 ('lists every hostname under a domain') plus the exact data source condition (unexpired publicly-logged TLS certificates). This clearly separates it from the sibling `dns`, `ssl`, and `rdap` tools, which cover different record types.

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 explicit use cases ('attack-surface mapping, asset inventory or competitive research') and rules out a near alternative ('Only names in public certificates, no DNS brute force'), which usefully steers agents away from brute-force enumeration. It does not name a sibling tool by name as the fallback choice, so it stops short of a 5.

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