Check if a domain can be email-spoofed

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false. The description adds valuable context beyond these: it explicitly states the check uses only public information (DNS and HTTP requests), performs no port scanning or exploit testing, and explains how findings are structured. This exceeds the annotation coverage with relevant operational details.

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 appropriately detailed but not bloated; it front-loads the core answer in the first sentence and then expands on scope, return format, and security posture. Each sentence contributes useful information, and the alternative usage note is placed at the end. Slightly longer than strictly necessary, but every part earns its place.

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 only one parameter and no output schema, the description carries the burden of explaining behavior and returns. It explicitly mentions the 0-100 score and findings tied to specific records, ensuring the agent knows what to expect. It also covers input restrictions and the broader scope of use, making it fully complete for correct invocation.

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 schema fully documents the 'domain' parameter with constraints and a basic description. The tool description enriches this by specifying that bare domains work best, that full URLs or www prefixes are normalized, and that IP addresses, email addresses, or private/internal hostnames are refused. This adds practical guidance not present in the schema, going beyond the high coverage baseline.

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 clear, specific purpose: it answers whether a domain can be email-spoofed by checking SPF, DKIM, and DMARC records. It explicitly differentiates from the sibling scan_domain by scoping its focus to email authentication records and mentioning the broader alternative. This makes the tool's role unambiguous.

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 description provides explicit guidance on when to use this tool: for any question about email spoofing, phishing impersonation, DMARC/SPF/DKIM setup, or domain protection. It also names the alternative (scan_domain) for a broader security picture, giving clear when-to-use vs. when-not-to-use direction.

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