check_fcrdns

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

Discloses read-only nature and no auth required. Explains the multi-step process (PTR lookup, forward resolution, warnings). Lacks mention of potential latency but is otherwise transparent.

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?

Information-dense single paragraph, front-loaded with main purpose. Could be slightly more concise but effectively communicates all necessary details.

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 no output schema, description fully explains return values (per-IP PTR, forward result, verdict, warnings) and covers warnings types. Completely conveys what to expect.

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 has 100% coverage for the only parameter 'domain'. Description adds context about MX record retrieval but does not significantly enhance understanding 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?

Description clearly specifies the tool performs a read-only FCrDNS audit on IPs from domain's MX records, detailing each step. It distinguishes from siblings like check_blacklist by stating pairing for reputation signals.

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?

Explicitly states use cases: mail deliverability audits, debugging mail rejections, and suggests pairing with check_blacklist. No explicit 'when not to use' but the context is clear.

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