check_fcrdns

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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, destructiveHint=false Kubernete. The description reinforces these with 'Read-only' and 'No auth.' It adds detail on the exact steps performed (PTR lookup, forward resolution) and output contents (PTR value, forward result, match verdict, warnings), which is valuable behavioral context beyond annotations. However, it doesn't mention any rate limits or error handling, but given the read-only nature, this is acceptable.

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 concise and front-loaded. It states the purpose, method, outputs, and use cases in three sentences without fluff. Every sentence adds value.

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 the tool's simplicity (1 param, no output schema, but description details return values) and the presence of robust annotations, the description is fully adequate. Even though there's no output schema, the description lists the return components, which is sufficient.

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?

The description doesn't add significant parameter semantics because the schema already fully describes the single 'domain' parameter (100% coverage). The description implies it's a domain name but the schema already says 'Domain name only, e.g. example.com'. So baseline 3 is appropriate.

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 uses a specific verb ('audit') and clearly identifies the resource (every IP backing the domain's MX records) while explaining the FCrDNS verification process. It distinguishes itself from sibling tools like check_blacklist by specifying its unique focus on reverse DNS validation.

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 usage scenarios: 'mail deliverability audits, SpamExperts-style cluster checks, and any why is our mail being rejected debugging' and recommends pairing with check_blacklist for reputation signals. This gives clear guidance on when to use and complements alternatives.

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