mail_dns_check

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

Annotations already declare readOnlyHint=true and openWorldHint=true, and the description adds real context beyond them: it performs live DNS queries, reads local postconf values (myorigin/mydomain, smtp_bind_address, myhostname) and opendkim log lines to derive defaults, and probes common DKIM selector names as a fallback. It stops short of disclosing timeout or rate-limit behavior.

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 sentence with a tight enumerated list where every clause names a distinct check performed (SPF 10-lookup limit, DKIM key size, DMARC reporting). Dense but no filler; slightly long for one sentence but nothing 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?

An output schema exists, so return values need not be described, and the annotations cover the safety profile. The description thoroughly scopes what is checked; the only gap is routing guidance against sibling diagnostic tools.

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% with all three parameters documented, so the schema already carries the semantics; the description adds only the 'against myhostname' context. Baseline 3 is appropriate – no additional syntax or format guidance is provided beyond the schema.

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 concrete verb (check) and resource (DNS records receivers use to accept/reject mail) and enumerates the exact record families inspected: MX, SPF, DKIM, DMARC, PTR/FCrDNS. This is clearly distinct from every sibling, which are postfix config/queue/log tools – an agent can route to it without opening a schema.

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?

Usage is implied by the diagnostic framing (mail deliverability/authentication troubleshooting) but the description never states when to choose this over siblings like postfix_doctor, nor any exclusions or prerequisites. Adequate but leaves the when-to-use decision to inference.

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