Check a domain for subdomain-takeover risk

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

The description goes well beyond the annotations. It discloses that the tool sends a small number of ordinary HTTPS GET requests to subdomains, resolves a fixed list of common subdomain names, and never registers, claims, or modifies anything. These details are not captured by readOnlyHint=true or other annotations and give the agent a clear picture of the tool's network behavior and safety profile. No contradiction with annotations.

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 description is front-loaded with the purpose, then explains the mechanism, clarifies non-actions, and ends with usage guidance. It is slightly long but every sentence carries relevant information—no fluff. The structure is logical and the critical safety points (HTTP requests, no modification) are given prominent placement. It earns a 4 rather than 5 because it could be tightened slightly without losing meaning.

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, so the description must explain return values—it does: 'Returns a 0-100 score plus a finding per at-risk record, naming the record and the service it points to.' It also covers behavior, network impact, safety limits, and use cases. For a single-parameter tool with no nested objects, nothing an agent needs to call it correctly is missing.

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?

The only parameter, 'domain', is fully documented in the schema with type, length constraints, accepted formats (bare domains best, URL or www. normalised), and exclusions (IP, email, private/internal hostnames). The tool description does not add any parameter-specific details beyond what the schema already covers. Since schema coverage is 100%, the baseline of 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 a precise question, 'does this domain have DNS records pointing at services someone else could claim?', and immediately states it inspects DNS records for dangling CNAMEs. This clearly distinguishes it from siblings like check_tls or check_security_headers, which target other concerns. The verb 'check' and the resource 'domain for subdomain-takeover risk' are specific and actionable.

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 explicitly states when to use: 'Use this for dangling DNS, abandoned cloud resources, or subdomain hijacking risk.' It also clarifies what it does not do ('no port scanning and no exploit testing'), which implies exclusions. However, it does not explicitly name alternative tools or spell out when NOT to use it, though the sibling list makes those obvious. That is a minor gap from a 5.

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