Unstuck

Check Domain Availability

domain_check

Read-onlyIdempotent

Check if a domain name is available to register. Looks the domain up in the official registry (RDAP) and says whether it is already taken or appears free to buy. Use it to find an available domain for a new business, product, or website name. Price: $0.005 per successful call; failed calls are free. Free to try: a few calls a day without a key.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "domain": "<domain>"
    },
    "name": "domain_check"
  }
}

Input Schema

Name	Required	Description	Default
`domain`	Yes	The domain name to check, e.g. "mycoolstartup.com".
`api_key`	No	Your Unstuck API key, if this connection has none. Leave empty to try free tools or to get a key and payment link.

Output Schema

Name	Required	Description
`note`	Yes	How to read the answer.
`domain`	Yes	The registrable domain that was checked.
`source`	Yes	Where the answer came from.
`available`	Yes	True if no registration was found.
`balance_usd`	Yes	Remaining prepaid balance, USD.
`charged_usd`	Yes	Amount charged for this call, USD.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 4, 2026

addedInput schema / properties / api_key

Added value: +{
+  "description": "Your Unstuck API key, if this connection has none. Leave empty to try free tools or to get a key and payment link.",
+  "maxLength": 200,
+  "type": "string"
+}

First observedOct 4, 2026

TDQS

A4.1/5.0

Behavior5/5

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

Annotations already cover read-only, idempotent, open-world and non-destructive behavior, and the description adds genuinely new operational context: a $0.005 per successful call price, free failed calls, a no-key free tier of a few calls a day, and the RDAP source. It also hedges appropriately with 'appears free to buy', signalling registry-lookup limits rather than guaranteeing purchasability.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Purpose and behavior come first, followed by usage and then cost/access details in compact sentences with no filler. Slight redundancy between 'says whether it is already taken or appears free to buy' and the opening availability statement, but the structure is well front-loaded.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return-value explanation is unnecessary, and the description still covers the remaining agent-facing unknowns: cost per call, free failures, no-key trial limits, and the data source. Nothing an agent needs in order to decide to call this tool is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and both parameters are documented in the schema (including the example domain and the optional api_key/free-trial semantics), so the description is not required to compensate. It adds nothing about parameter formatting or edge cases beyond what the schema already states, matching the baseline for full-coverage schemas.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Check if a domain name is available to register') and even names the lookup mechanism (official registry / RDAP), so the agent knows exactly what the tool returns. It does not explicitly differentiate itself from the sibling domain_info, which an agent might reasonably confuse it with, so it falls short of a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a concrete use case ('find an available domain for a new business, product, or website name') that tells the agent when this tool is appropriate. It offers no when-not guidance or named alternatives (e.g. use domain_info when the domain is already registered and you want details), so it stops short of explicit routing.

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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