compare_tldsCompare registrar prices across up to 20 extensions side by side.
| Name | Required | Description | Default |
|---|---|---|---|
| tlds | 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?
Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=true, so the safety and determinism profile is fully covered. The description adds only the 'up to 20 extensions' bound, which is a behavioral constraint but also duplicates the schema's maxItems=20. No pricing volatility, caching, or result-ordering behavior is disclosed.
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 with no filler or repetition. It is efficiently sized, though the brevity is what leaves the usage and parameter gaps unaddressed.
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, one-required-parameter comparison tool with no output schema, the description covers what is needed to invoke it correctly. The remaining gap is routing ambiguity among the price-related siblings, which is a usage concern rather than a completeness failure for this low-complexity tool.
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-schema, tlds is not). The description partially compensates by clarifying that the array elements are extensions ('TLDs') and that at most 20 are accepted, but it adds no format guidance (leading dot or not, case, duplicates) for the undocumented required parameter.
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+resource: comparing registrar prices across extensions, with the cardinality bound (up to 20) included. This is clearly distinct in kind from a single-lookup tool like get_tld_prices, but the description never explicitly names or distinguishes itself from siblings such as find_cheapest_tlds or get_tld_prices.
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 guidance, no exclusions, and no mention of the obvious alternative find_cheapest_tlds or get_tld_prices. An agent must infer from the name alone that this is the multi-TLD side-by-side option rather than the cheapest-pick or single-price option.
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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