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solverio-pl

nip-checker-mcp

by solverio-pl
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JavaScript
Remote

Polish NIP Checker MCP Server

A Model Context Protocol (MCP) server for checking Polish NIP (Tax Identification Numbers) using the official Ministry of Finance VAT taxpayer database.

Features

  • ✅ Real-time NIP verification using official Polish Ministry of Finance API

  • ✅ Bank account verification - check if bank account belongs to specific NIP

  • ✅ Automatic date handling - defaults to current date

  • ✅ Input normalization - handles NIP formats with or without hyphens

  • ✅ Comprehensive error handling and validation

  • ✅ Ready for Claude Desktop - works seamlessly with AI assistants

Related MCP server: Polish Business Intelligence MCP

Quick Start with npx (Recommended)

Add this to your Claude Desktop configuration:

{
  "mcpServers": {
    "nip-checker": {
      "command": "npx",
      "args": ["-y", "@solverio-pl/nip-checker-mcp@latest"]
    }
  }
}

Installation Options

Option 1: Direct npx usage (No installation needed)

npx @solverio-pl/nip-checker-mcp@latest

Option 2: Global installation

npm install -g @solverio-pl/nip-checker-mcp
nip-checker-mcp

Option 3: Local development

git clone https://github.com/solverio-pl/nip-checker-mcp.git
cd nip-checker-mcp
npm install
npm run build
npm start

Available Tools

check_nip

Verify Polish NIP in the VAT taxpayer database.

Parameters:

  • nip (required): Polish NIP number (10 digits, hyphens optional)

  • date (optional): Date for verification (YYYY-MM-DD format, defaults to today)

Example:

Check NIP 9491626103

check_nip_bank_account

Verify if a bank account is assigned to a specific NIP.

Parameters:

  • nip (required): Polish NIP number (10 digits)

  • bankAccount (required): Bank account number (26 digits)

  • date (optional): Date for verification (YYYY-MM-DD format)

Example:

Verify if account 38109017950000000151316514 belongs to NIP 9491626103

Sample Output

✅ NIP Verification Results

**NIP**: 9491626103
**Company**: JANUSZ CHALIMONIUK
**VAT Status**: Czynny (Active)
**Address**: BURSZTYNOWA 73D, 42-202 CZĘSTOCHOWA
**Registration Date**: 2022-09-01
**Bank Accounts**: 38109017950000000151316514
**REGON**: 240070517
**Virtual Accounts**: No

**Request Details**:
- Request ID: rLtV8-9471ak2
- Query Date: 02-08-2025 09:29:38

Claude Desktop Configuration

Windows

Edit: %APPDATA%\Claude\claude_desktop_config.json

macOS

Edit: ~/Library/Application Support/Claude/claude_desktop_config.json

Full configuration example:

{
  "mcpServers": {
    "nip-checker": {
      "command": "npx",
      "args": ["-y", "@solverio-pl/nip-checker-mcp@latest"]
    }
  }
}

Personal Settings Addition

Add this simple line to your Claude personal settings for automatic usage:

NIP Checker: When user asks to check/verify/lookup a Polish NIP number, use the check_nip MCP tool automatically.

Usage Examples

Once configured, you can simply ask:

  • "check nip 9491626103"

  • "verify nip 123-456-78-90"

  • "lookup nip 9491626103 for yesterday"

  • "is account 38109017950000000151316514 assigned to nip 9491626103?"

API Source

This tool uses the official Polish Ministry of Finance API:

  • Base URL: https://wl-api.mf.gov.pl/

  • Documentation: Available at the API endpoint

  • Data Source: Official VAT taxpayer registry ("Biała Lista Podatników")

Requirements

  • Node.js 18.0.0 or higher

  • Internet connection for API access

License

MIT License - see LICENSE file for details.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Support

For issues and feature requests, please use the GitHub Issues page.

Made with ❤️ by Solverio for the Polish business community.

Available Tools

2 tools
check_nipB

Check Polish NIP (Tax Identification Number) in the Ministry of Finance VAT taxpayer database

ParametersJSON Schema
NameRequiredDescriptionDefault
nipYesPolish NIP number (10 digits, hyphens optional)
dateNoDate for verification (YYYY-MM-DD format, optional - defaults to today)

TDQS

B3.3/5.0
Behavior2/5

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

With no annotations, the description carries the full burden. It mentions the data source (Ministry of Finance VAT taxpayer database) but does not disclose behavior such as read-only nature, response format, error cases, or potential rate limits. The description adds minimal behavioral context beyond the name.

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

Conciseness5/5

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

The description is a single, concise sentence that front-loads the action and key context. Every word earns its place, with no unnecessary filler.

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

Completeness3/5

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

The tool is simple with two well-documented parameters, and the description covers the core purpose. However, without an output schema or annotations, it does not explain what the check returns (e.g., registration status, boolean result), and it omits any reference to the optional date parameter, leaving some context gaps.

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%, so the schema already documents both parameters. The description adds context for 'nip' as a Polish Tax Identification Number, but does not elaborate on the 'date' parameter or its default behavior, providing only marginal value beyond the schema.

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?

Clearly states the tool checks a Polish NIP against the Ministry of Finance VAT taxpayer database, using a specific verb and resource. This distinguishes it from the sibling tool check_nip_bank_account, which focuses on bank account verification.

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

Usage Guidelines2/5

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

Provides no guidance on when to use this tool versus the sibling check_nip_bank_account, nor any scenarios for use. The description is purely functional and lacks context for selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

check_nip_bank_accountA

Verify if a bank account is assigned to a specific NIP

ParametersJSON Schema
NameRequiredDescriptionDefault
nipYesPolish NIP number (10 digits)
dateNoDate for verification (YYYY-MM-DD format, optional)
bankAccountYesBank account number (26 digits)

TDQS

A4/5.0
Behavior3/5

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

No annotations are provided, so the description must carry the full behavioral burden. The verb 'verify' strongly implies a read-only operation, but the description does not explicitly state there are no side effects, permissions required, or other relevant behavioral details. It is not misleading, but minimal.

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

Conciseness5/5

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

The description is a single clear sentence with no redundant words or repetition. It earns its place by stating exactly what the tool does.

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

Completeness4/5

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

The tool is simple, with all parameters documented in the schema. The description fully captures the action and implies a boolean result. It lacks explicit mention of return format or any edge cases, but given the simplicity, it is nearly complete.

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 description coverage is 100%, with each parameter (nip, date, bankAccount) already documented with types, patterns, and descriptions. The description adds no additional parameter-level semantics beyond reminding that the bank account is being verified against a NIP. Baseline 3 is appropriate.

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?

The description uses a specific verb ('verify') and resource ('bank account assigned to a specific NIP'), clearly distinguishing it from the sibling tool 'check_nip' which likely just checks NIP validity. The purpose is unambiguous and actionable.

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?

The description clearly states the tool's context (verifying bank account assignment to a NIP) but does not explicitly mention alternatives or exclusions. The sibling tool 'check_nip' provides implicit contrast, but no direct guidance is given in the description.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. 2 tool updatesv1.0.4
    • First observedcheck_nip
    • First observedcheck_nip_bank_account
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TDQS

A3.9/5.0
Disambiguation5/5

The two tools have completely distinct purposes: one checks the NIP itself against the VAT database, the other verifies a bank account against a NIP. There is no overlap or ambiguity in their functions.

Naming Consistency5/5

Both tool names follow the same verb_noun pattern: check_nip and check_nip_bank_account. The pattern is predictably extended with a qualifier, maintaining consistency.

Tool Count4/5

With only 2 tools, the server is minimal but well-scoped for its narrow purpose (NIP validation). It falls slightly below the typical 3-15 range, but the focus on two core operations makes the count appropriate.

Completeness5/5

The server covers the two essential operations for its domain: validating a NIP and verifying a bank account association. No obvious gaps exist for the stated purpose of a NIP checker.

Maintenance

ActivityInactive
ResponsivenessNo issues

Resources

Unclaimed servers have limited discoverability.

Looking for Admin?

If you are the server author, to access and configure the admin panel.

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