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

Annotations already indicate read-only, idempotent, non-destructive behavior, and the description adds significant extra context: it is passive DNS-only (no SMTP probe), DKIM probing tests common selectors and recent dates, custom selectors must be supplied, and there are rate limits (30/hr free, 500/hr Pro). These details help the agent understand side effects, constraints, and operational limitations beyond the 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 information-dense and front-loaded with the primary purpose, then usage, scoring details, probing behavior, and rate limits. It is slightly longer than necessary but every sentence contributes meaningful information. No fluff, though the run-on structure could be improved for readability.

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 presence of an output schema, the description does not need to explain return values. It covers the main purpose, protocols, scoring scale, probing behavior, passive nature, and rate limits. It is complete for an agent to understand what the tool does, how it behaves, and what parameters to supply. The description also helps differentiate it from numerous sibling security tools.

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 already covers both parameters well (100% coverage). The description enhances the 'selectors' parameter by explaining that it supplies custom DKIM selectors and that probing defaults to common selectors with recent dates. This gives the agent insight into how the parameter is used and what happens if omitted, adding value beyond the schema descriptions.

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 clearly states the tool analyzes email authentication posture (SPF, DMARC, DKIM) and produces a numeric score and findings. It specifies the resource (domain) and the specific protocols, and distinguishes itself from sibling tools like email_mx or email_verify by focusing on authentication posture. The dual-use framing (red-team/blue-team) further clarifies its purpose.

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 clear context for when to use the tool: for red-team spoofing feasibility and blue-team posture audits. It does not explicitly name alternative tools or state when not to use it, but the context is enough for an agent to decide in most scenarios. The sibling tool list shows related tools, but the description itself doesn't draw explicit comparisons.

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