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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, but the description still adds real behavioral context: fallback and throttling logic between certspotter and crt.sh, the keyless rate limit implied by page reads, the 40-name cap on DNS resolution, and the fact that nothing is sent to the target. That is meaningfully more than the annotations convey.

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?

It is a single dense paragraph, front-loaded with the core action and source behavior, with return shape and caveats following in a sensible order. The authorization sentence and some source detail restate schema content, but nothing is egregiously wasteful.

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?

There is no output schema, and the description compensates fully by enumerating the return payload: deduplicated hostnames, first/last seen issuance dates, certificate count, issuers, wildcard coverage flag, and the wildcard entry list. An agent knows both how to call it and what it will get back.

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 coverage is 100%, so the schema already documents all six parameters, including enum and default values. The description reinforces source selection and the resolve cap and adds the useful detail that resolution 'marks live hosts', but most of what it says about parameters duplicates the schema rather than extending it.

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?

The description states a specific verb and resource — passive subdomain enumeration for a domain from certificate transparency logs — and names the concrete data sources (certspotter, crt.sh). It implicitly separates itself from resolve_subdomains by emphasizing 'passive' and 'nothing is sent to the target', but it never names the siblings, so an agent must infer the boundary rather than being told it.

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?

It gives clear operating context: passive-only lookup, a source-selection rule (auto/certspotter/crtsh, crt.sh for expired history), and an authorization caveat ('assets you own or are authorised to test'). What it lacks is explicit routing against the siblings — e.g. when to follow up with resolve_subdomains or get_certificate_history instead of setting resolve=true here.

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