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

With no annotations, the description carries the full behavioral burden, yet it only states what is checked. It does not disclose that this is a passive DNS-based lookup, whether it requires authentication, whether results are cached, or what a failure/ambiguous result means. Read-only behavior is only weakly implied by 'check'.

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 front-loaded phrase with no filler; the core resource and scope are immediately visible. It is arguably too terse rather than padded, but nothing in it is wasteful.

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 one-parameter tool with no output schema and no annotations, the description should at least indicate the shape of the result (record presence, pass/fail, missing-record warnings) and how it differs from email_validate. Neither is provided, leaving the agent unable to predict the response.

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 0%, so the description must compensate. It implies the input is a domain (not an email address or URL), which is some added meaning, but it does not specify expected format (bare domain, trailing dot, subdomain, punycode) for the single required parameter.

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 names a specific check type (anti-spoofing) with the exact standards inspected (SPF/DMARC/DKIM) and scopes it to a domain, so the purpose is concrete. However, it does not differentiate itself from the many sibling email tools (email_validate, email_verify, email_disposable), which an agent must disambiguate by name alone.

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?

There is no statement of when to use this tool versus the closely-named siblings email_validate/email_verify/email_disposable, nor any preconditions or typical invocation context. The agent is left to infer usage from the name alone.

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