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

No annotations are provided, so the description carries the full burden. It meaningfully discloses that SPF, blacklist, and reverse-DNS checks are not possible from a static .eml file, and it implies a non-live, non-SMTP analysis mode. It does not describe return format or side effects, but the limitation disclosure is substantive for this tool.

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 compact and front-loaded: purpose first, then the critical limitation and alternative, then a brief contextual note. Every sentence contributes to agent decision-making, with no redundant verbiage.

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?

For a single-parameter tool with no output schema and no annotations, the description provides enough context to invoke it correctly: it defines the input, explains the offline scope, and points to create_mailtest when authoritative verification is needed. The only minor gap is that it does not describe what the analysis returns.

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 input schema already fully describes the sole parameter (eml as 'The complete raw email source (headers + body)'), and the description's mention of 'full headers + body' adds little beyond the schema. With 100% schema description coverage, the baseline is 3; the description adds no encoding, size, or format constraints.

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 specific action ('Run a deliverability/content analysis') on a specific resource ('raw RFC 822 email' with 'full headers + body'). It also distinguishes itself from create_mailtest by framing this as a file-based offline analysis, making selection straightforward relative to siblings like check_blacklist and check_spoofability.

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 explicitly names a limitation ('with no live SMTP session, SPF, blacklist and reverse-DNS cannot be verified from a file') and gives a direct alternative ('for the authoritative score use create_mailtest instead'). This gives an agent clear when-to-use and when-not-to-use guidance.

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