check_subdomain_takeover

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

Annotations already cover safety (readOnly, idempotent, non-destructive). The description adds concrete scope detail ('16 provider families' and lists them) and warns that discover_subdomains returns only a CT sample, not a full inventory. This is additive context, though it doesn't disclose the default 15-name built-in sweep (which is documented in the schema).

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: the first states the core purpose, the second lists coverage, the third gives usage and pairing guidance. No filler or redundant repetition; each sentence contributes meaningfully.

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?

Given the rich schema, output schema, and annotations, the description covers the key facts an agent needs: what the tool does, when to invoke it, and a caveat about widening the candidate set. The default 15-name sweep is documented under the subdomains parameter, so it need not be repeated. The description is complete for this complexity level.

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?

All four parameters are fully described in the input schema (100% coverage). The description itself does not add parameter-level semantics beyond the schema—its extra notes about provider families and pairing are about output scope and workflow, not parameter meaning. 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?

The description opens with 'Sweep subdomains for dangling CNAMEs pointing to deprovisioned cloud services that could be claimed by an attacker,' clearly stating the verb, resource, and vulnerability. It lists provider families, distinguishing it from sibling DNS checks like check_mx or check_spf.

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?

Explicitly states 'Use when asked if subdomains are pointing to deprovisioned cloud services' and gives a complementary action with 'Pair with discover_subdomains to widen the candidate set.' This provides clear when-to-use context and an alternative tool.

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