Email deliverability signals for a domain: MX records, SPF policy, DMARC policy, plus checks and an overall verdict (poor/fair/good/excellent). [PAID: $0.015 USDC per call via x402]
| Name | Required | Description | Default |
|---|---|---|---|
| domain | Yes | Domain to check (e.g. example.com) |
Changes observed during successful MCP inspections.
Input schema / additionalPropertiesPrevious value: -trueNew value: +falseInput schema / properties / domainAdded value: +{
+ "description": "Domain to check (e.g. example.com)",
+ "type": "string"
+}Input schema / properties / promptRemoved value: -{
- "description": "Input prompt for this service.",
- "type": "string"
-}Input schema / requiredPrevious value: -[
- "prompt"
-]New value: +[
+ "domain"
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It does disclose a genuinely useful behavioral fact — the $0.015 USDC per-call cost via x402 — and enumerates the verdict scale, but it says nothing about rate limits, failure modes, or what happens for domains with no SPF/DMARC records.
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 that leads with the resource and result set, with the pricing tag bracketed at the end. Every clause earns its place, though the enumeration is dense.
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?
With no output schema and no annotations, the description compensates by naming the returned fields and the verdict scale, and it discloses the payment requirement. For a one-parameter lookup this is nearly complete; only error/no-record behavior is unaddressed.
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% for the single 'domain' parameter, so the schema already documents it fully. The description adds no syntax or constraint detail (e.g. TLD-only, subdomain handling) beyond what the schema states, which is the baseline case.
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 resource (email deliverability signals for a domain) and enumerates the exact outputs (MX, SPF, DMARC, verdict), so an agent knows precisely what it returns. It is distinguishable from the sibling liminal-dns-lookup by its email-deliverability framing, but it never explicitly says how it differs from that overlapping tool.
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 when-to-use or when-not-to-use guidance, and no alternatives are named. The only implied context is that you call it with a domain you want scored for deliverability; nothing routes the agent between this and liminal-dns-lookup.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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