Live availability check for a full domain name (RDAP, WHOIS fallback). available is null if the registry could not be reached.
| Name | Required | Description | Default |
|---|---|---|---|
| domain | Yes | ||
| api_key | No | Your TLDers API key. Only needed if your client cannot send an Authorization header or use a ?key= URL. |
Changes observed during successful MCP inspections.
Input schema / properties / api_keyAdded value: +{
+ "description": "Your TLDers API key. Only needed if your client cannot send an Authorization header or use a ?key= URL.",
+ "type": "string"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full behavioral burden. It usefully discloses the RDAP-with-WHOIS-fallback strategy and, importantly, that 'available' is null when the registry is unreachable — a semantic an agent cannot get from the schema. It does not mention rate limits, latency, or the ambiguity of a null result for downstream decisions.
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?
Two short sentences with no filler; the primary purpose is front-loaded and the null-result caveat follows immediately. Every sentence earns its place.
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?
There is no output schema, so the description should characterize the return value. It explains only the 'available' field's null case and omits the rest of the response shape (e.g. what accompanies a true/false result). Adequate but with a clear gap for a lookup whose only purpose is its return value.
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 coverage is 50%: api_key is documented in the schema, but the required 'domain' parameter has no schema description. The description's phrase 'full domain name' partially compensates by implying the expected input form (e.g. example.com rather than a bare label), but no format example or validation rule is given.
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?
States a specific verb and resource ('availability check for a full domain name') and names the mechanism (RDAP, WHOIS fallback). It is trivially distinguishable from the sibling pricing/registrar tools, none of which check availability.
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?
The description explains what the tool does but gives no when-to-use context, no prerequisites, and no exclusions relative to alternatives. An agent must infer that this is the tool for pre-registration checks 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.
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