list_registrarsEvery domain registrar TLDers tracks, with WHOIS-privacy info and number of tracked TLDs.
| Name | Required | Description | Default |
|---|---|---|---|
| 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?
Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description usefully adds what the response contains (WHOIS-privacy info, number of tracked TLDs), which matters since there is no output schema, but it says nothing about pagination, auth scope, or result size.
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 states the resource and its payload with no filler. It is a fragment rather than a full sentence, but it wastes no words.
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?
For a simple read-only enumeration tool with full annotation coverage and one fully documented parameter, the description covers what is returned and its scope. Nothing critical is missing for an agent to call it correctly, though return volume or ordering 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%, so the single api_key parameter is fully documented in the schema, including the fallback auth conditions. The description adds nothing beyond the schema, which is the expected baseline here.
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?
Names a specific resource (registrars) and the verb implied by the name (list), and adds scope detail: WHOIS-privacy info and count of tracked TLDs. It is distinguishable from the TLD/price-oriented siblings, though it doesn't explicitly say how it differs from them.
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?
No when-to-use guidance, no prerequisites, and no mention of alternatives such as get_tld_prices or compare_tlds. The usage is only implied by the tool name.
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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