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

Annotations already declare readOnlyHint and idempotentHint, so the description adds value by disclosing the specific checks performed (DMARC/SPF/DKIM alignment and policy strength) and the $2 cost. This goes beyond what annotations provide and helps the agent understand what the tool does without contradicting 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 extremely concise with only two sentences. It front-loads the core purpose and includes essential operational context (cost, relationship to sibling tool) without any fluff. Every word 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?

Given the tool's moderate complexity and lack of output schema, the description provides a good high-level overview but has gaps. It does not describe the return format, what include_mx_analysis does, or any details about how the DMARC/SPF/DKIM analysis is presented. The core purpose is clear, but the missing parameter semantics and output behavior make it only minimally complete for an agent to use it correctly.

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 description coverage is only 33% (only previous_scan_id is described). The description does not mention or explain any parameters, leaving include_mx_analysis completely unexplained. Since the schema coverage is low, the description should have compensated by explaining parameter meaning, but it does not. Only 'domain' is self-evident from the context.

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 the tool's purpose with a specific verb and resource: 'Full email-security posture for a domain: whether mail from it can be spoofed, with DMARC/SPF/DKIM alignment and policy strength.' This is a clear and specific definition that distinguishes it from sibling tools like dns_security_check by explicitly stating it is a 'superset' for the email question.

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 usage context by noting 'A superset of dns_security_check for the email question specifically,' which helps an agent choose this tool over alternatives. It also mentions the $2 per-call cost, which is relevant for decision-making. However, it does not explicitly state when not to use it or name alternatives beyond dns_security_check.

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