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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds genuine behavioral context beyond that: it is a non-blocking snapshot ('without waiting') that aggregates several processing stages (Proxy Mail QA limits, Cloudflare SPF/DKIM/DMARC rejections) and may return a diagnostic hint rather than raw counts.

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?

Purpose and output contents are front-loaded in the first sentence, with the usage instruction in a short second sentence. The first sentence is dense and list-heavy, but every clause names a distinct category of result, so little 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?

With no output schema, the description must describe returns, and it does: arrival counts, last-arrival timing, refusal reasons, rejection reasons, and hint text. For a one-parameter read-only diagnostic, nothing an agent needs in order to call or interpret it is missing.

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?

There is a single parameter at 100% schema description coverage, and the schema already documents the variant/+tag behavior thoroughly. The description adds no additional parameter semantics, so the baseline 3 applies.

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 verb and resource ('Explains an address's mail without waiting') and enumerates exactly what it reports: arrival count, last arrival time, QA refusals, Cloudflare rejections by SPF/DKIM/DMARC, and delivery hints. This clearly separates it from the wait_* and check_email siblings, which block or examine a single message rather than summarizing an address's whole delivery picture.

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?

'Use it when a wait finds nothing' gives an explicit trigger condition that routes the agent here after a wait_for_code/wait_for_link failure, and 'tell the person what it says' prescribes follow-up behavior. It does not name the alternative wait tools explicitly or state when not to use it, so it stops short of full when/when-not guidance.

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