Click on "Deploy Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type @ followed by the MCP server name and your instructions, e.g., "@Japan Area Code MCP Server find area code for Tokyo"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
A Model Context Protocol (MCP) server that provides access to Japanese statistical standard area codes (標準地域コード). This server fetches data from the official Japanese government CSV file and provides tools to list and search area codes.
Clone or download this repository
Install dependencies:
npm installBuild the project:
npm run buildRelated MCP server: estat-mcp
To use this MCP server with Cursor or other MCP-compatible clients, add it to
your MCP configuration file (typically ~/.cursor/mcp.json):
{
"mcpServers": {
"japan-areacode-mcp": {
"command": "node",
"args": ["/path/to/japan-areacode-mcp/dist/index.js"]
}
}
}Make sure to replace /path/to/japan-areacode-mcp with the actual path to this
project.
The server provides two tools: list-areacode and find-areacode
list-areacodeLists all area codes from the official Japanese government CSV file.
None
find-areacodeFinds an area code by searching for a prefecture or municipality name.
Parameter | Type | Required | Description |
| string | Yes | Search query that can match prefecture name, municipality name, or yomigana |
Data source: https://www.soumu.go.jp/main_content/000323625.csv
Find the area code of a given prefecture
| Name | Required | Description | Default |
|---|---|---|---|
| query | Yes |
| Name | Required | Description |
|---|---|---|
| data | Yes |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations exist, and the description does not disclose any behavioral traits such as error handling, assumptions about input, or potential side effects. For a simple lookup, minimal disclosure is needed, but zero transparency is insufficient.
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?
The description is a single, concise sentence that directly states the tool's purpose with no unnecessary 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?
Given the tool's simplicity (one parameter, straightforward lookup) and the presence of an output schema, the description is reasonably complete. However, it could mention that the output is an area code.
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 0%, so the description must compensate. It clarifies that 'query' refers to a prefecture, but does not specify format (e.g., full name, partial match) or constraints. This adds partial meaning but not enough to address the gap fully.
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?
The description uses the specific verb 'Find' and resource 'area code' with 'given prefecture', clearly distinguishing from sibling 'list-areacode' which likely lists all codes.
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 explicit when-to-use or when-not-to-use guidance. The context implies it's for looking up an area code by prefecture, but does not specify input format or mention the sibling tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
List all area codes
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
| Name | Required | Description |
|---|---|---|
| data | Yes |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description must fully disclose behavior. It only states the action with no mention of return format, pagination, authentication, or performance implications.
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?
The description is extremely concise at four words, front-loading the key information. It is efficient for a simple tool, though it could be slightly more descriptive without losing brevity.
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?
Given the tool's simplicity (no parameters, list operation) and an output schema existing, the description is minimally adequate. However, it lacks usage guidance relative to the sibling tool and does not set user expectations about the output.
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?
The tool has zero parameters and the schema coverage is 100% by default. The description adds no parameter information, which is acceptable as there is nothing to describe.
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?
The description 'List all area codes' uses a specific verb ('list') and resource ('area codes'), clearly distinguishing the operation from the sibling tool 'find-areacode' which implies search or filter functionality.
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?
Usage is implied by the name and description, but there is no explicit guidance on when to use this tool vs 'find-areacode' or any context about prerequisites.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
v1.0.0find-areacodelist-areacodeScored across 2 tools
Each tool has a clearly distinct purpose: one retrieves a specific area code given a prefecture, the other lists all area codes. No ambiguity or overlap exists.
Both tools follow a consistent verb-areacode pattern using lowercase with hyphens (find-areacode, list-areacode), making them predictable and easy to interpret.
With only two tools, the scope is narrow but appropriate for a read-only area code lookup service. It could potentially include a reverse lookup, but the count is reasonable for the stated purpose.
The tool set covers the essential operations for area codes: querying a specific prefecture and listing all. A minor gap is the lack of a search-by-code function, but the basic use cases are addressed.
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