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

Annotations already declare read-only, open-world, idempotent, non-destructive behavior. The description adds useful context by explaining DNS-based checks, conditional checks, and explicitly naming unchecked requirements (complaint rate, per-connection TLS) rather than passing them. It does not detail return format, but the limitation disclosure is valuable.

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?

A single dense sentence front-loads the purpose and packs all checks and conditions. 'Sorted honestly' is slightly editorial and the semicolon list is long, but no substantive content is wasted.

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 composite complexity and rich annotations/schema, the description covers scope, conditional inputs, and limitations. It lacks an explicit description of return values, though 'named as not checked rather than passed' partially indicates result semantics.

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 coverage is 100%, so the baseline is 3, but the description adds meaning beyond the schema for optional ip (forward/reverse DNS) and headers (one-click unsubscribe and From alignment). The domain parameter's role in DNS checks is implied rather than restated.

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?

States a specific resource (Gmail/Yahoo/Microsoft bulk sender requirements) and enumerates the checks performed, distinguishing it from single-purpose siblings like check_spf and check_dmarc. It also explicitly scopes what is and is not covered.

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?

Gives clear context by specifying that ip enables forward/reverse DNS and headers enable unsubscribe/alignment checks, implying this is the composite compliance check. It does not name alternative sibling tools or when to prefer them.

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