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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the description's job is lighter. The description adds value by explaining the non-blocking SMTP probe behavior (states smtp_status values like 'pending', 'running', 'complete'), the capping logic for the letter grade, and that results appear in checks. No contradiction with 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 a single paragraph of moderate length, packed with utility. Every sentence contributes essential details (scope, output format, polling behavior). It is front-loaded with the core purpose. Could be slightly more structured (e.g., bullet points for checks), but no redundant or irrelevant content.

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 only 2 parameters, full schema coverage, an output schema (which explains return values), and read-only/open-world annotations, the description is complete: it covers what the tool does, what the output contains, how to handle the SMTP probe, and differentiates from siblings. Missing prerequisites (e.g., DNS access) are implied by the nature of the check.

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 100%, providing a baseline of 3. The description adds meaning beyond the schema by explaining the purpose of include_smtp (live probe, non-blocking, polling behavior) and the implications of the poll loop, which the schema's 'Non-blocking' note only hints at.

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 opens with a specific verb ('Run') and enumerates the resources checked (MX, SPF, DKIM, DMARC, DNS health, provider detection, blacklists). It clearly distinguishes from the sibling tools like check_mx or check_spf by naming this a comprehensive 'full email and DNS deliverability check' that aggregates all those checks.

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 this tool—for a full deliverability check—and gives specific guidance on polling via the include_smtp parameter ('call this tool again...poll_after_seconds hints how long to wait'). While it doesn't explicitly exclude any siblings (e.g., 'use check_dkim if you only need DKIM'), the sibling differentiation is implicit in the comprehensive vs. single-check names.

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