WillItPlug

Will my plugs fit?

check_trip

Read-onlyIdempotent

Check whether devices from one country will work in another, for questions like "do I need an adapter for Japan?" or "will my UK charger work in the US?". Use when both a home country and a destination are known; for one country alone use country_plugs. Takes an English country name or ISO code for each. Returns which plugs fit, whether an adapter is needed, whether a voltage converter may be needed, frequency differences, local notes, a packing checklist and a page url.

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": {
      "from": "<from>",
      "to": "<to>"
    },
    "name": "check_trip"
  }
}

Input Schema

Name	Required	Description	Default
`to`	Yes	Where they are going, e.g. "Japan" or "jp".
`from`	Yes	Where the traveller lives and their devices come from, e.g. "United States" or "us".

Output Schema

Name	Required	Description
`to`	Yes
`fit`	Yes	How many of your plugs fit an outlet there.
`url`	Yes	The page on WillItPlug with the details.
`from`	Yes
`notes`	Yes	Things to know about the destination.
`plugs`	Yes	Each plug on the traveller's devices.
`credit`	Yes	Please credit WillItPlug with a link back when you use the data.
`reason`	Yes	The verdict in one sentence.
`version`	Yes
`voltage`	Yes
`adapters`	Yes	Adapters worth packing, by the outlet they fit.
`checklist`	Yes	What to pack and check, in English.
`adapterNeeded`	Yes
`usableOutlets`	Yes	Socket ids at the destination that take at least one of the plugs.
`converterNeeded`	Yes	maybe: check each device's label for its input voltage range.
`frequencyDiffers`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 10, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the description does not need to re-litigate safety. It adds real value by accepting either English names or ISO codes and by sketching the shape of the result (adapter/converter/frequency verdicts, notes, checklist, url), which sets expectations even though an output schema exists.

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?

Front-loaded with purpose and the disambiguating sibling reference, with example phrasings that are genuinely useful. The final sentence enumerating return fields is somewhat long and partly duplicates the output schema, costing a point on tightness.

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?

For a two-parameter, fully documented, read-only lookup with annotations and an output schema, nothing an agent needs is missing: purpose, preconditions, input format flexibility, alternative tool, and expected result categories are all present.

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

Parameters4/5

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

Schema description coverage is 100%, so the baseline is 3; the description earns the extra point by explicitly stating that either an English country name or an ISO code is acceptable for both parameters, and by framing 'from' as the traveller's home device origin rather than just a place name.

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

Purpose5/5

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

States a specific verb and resource — checking device/plug compatibility between two countries — and immediately distinguishes it from the sibling country_plugs by scope (two countries vs one). The illustrative questions ('do I need an adapter for Japan?') remove any ambiguity about what the tool answers.

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

Usage Guidelines5/5

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

Gives an explicit precondition ('use when both a home country and a destination are known') and names the alternative tool to use when only one country is known. That is the when-to-use plus the when-not-to-use rule in a single sentence.

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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