• VALID
  • INVALID
  • ERROR
  • HUMAN

How to validate NF-e access keys with your AI

Connect this MCP to your AI client once. After that, your agent handles the math to ensure your invoice keys are legitimate.

Ask AI about this page

Short answer

How do I check if an NF-e access key is valid?

Your AI runs the 44-digit key through a Modulo 11 mathematical check to confirm its structural integrity. This catches typos or malformed keys before you try to process them. You'll see the results of the validation immediately in your chat.

Where every issue lands.

Validation outcomes

The AI categorizes every key it checks based on the mathematical result.

VALID

Structural integrity confirmed

The AI confirms the key follows the Modulo 11 rule. You get a clean signal that the key is mathematically correct.

INVALID

Mathematical mismatch

The AI identifies that the checksum fails. This tells you the key is definitely wrong.

ERROR

Format violation

The AI detects that the input isn't a 44-digit string. It flags these as unusable inputs.

HUMAN

Manual review needed

If a key is mathematically valid but looks suspicious, the AI flags it for you to inspect manually.

The workflow

What your AI does when a key arrives.

The AI takes the raw string and runs it through a specific verification logic.

  1. Input parsing

    Your agent receives the 44-digit string and strips any accidental spaces or characters.

    verify_key_structure

  2. Checksum calculation

    The AI applies the Modulo 11 algorithm to the digits to calculate the expected check digit.

    verify_key_structure

  3. Integrity check

    The agent compares the calculated digit against the actual digit in the key to find mismatches.

    verify_key_structure

  4. Status reporting

    The AI delivers a clear pass or fail response based on the mathematical outcome.

    verify_key_structure

Try it

Copy these to start.

Use these prompts to trigger the validation process.

Starting points

Replace the bracketed text with your actual data, like a specific spreadsheet or a list of keys.

NF-e Validator Connector

You're all set. Choose your MCP client and follow the setup instructions.

Connector linkhttps://edge.vinkius.com/vk_preview_IRwsYmnDubhWF6CADb8mHPMbLhjrqO48Mkm0iChQ/mcp

Claude Desktop

Follow the steps below to connect in seconds.

  1. 1In Claude Desktop, open Settings → Connectors.
  2. 2Click “Add custom connector” and paste the connector link above as the remote MCP server URL.
  3. 3Click Add and start a new chat — NF-e Validator capabilities are ready to use.
Configuration · claude_desktop_config.jsonCopy
{
  "mcpServers": {
    "nf-e-access-key-validator-mcp": {
      "url": "https://edge.vinkius.com/vk_preview_IRwsYmnDubhWF6CADb8mHPMbLhjrqO48Mkm0iChQ/mcp"
    }
  }
}
Copy into chat04

  • Validate this NF-e key: [paste 44-digit key here]

  • Check this list of keys from my spreadsheet for structural errors: [paste list]

  • Can you verify if this access key is mathematically valid? [paste key]

  • Run a Modulo 11 check on these invoice keys: [paste keys]

  • Claude
  • ChatGPT
  • Cursor
  • VS Code
  • Windsurf
  • Claude Code
  • JetBrains
  • Cline

Start here

Connect NF-e Access Key Validator once, then ask.

One click connects this MCP to your preferred client. Your credentials stay encrypted, and you can start validating keys immediately.

Connect NF-e Access Key Validator to your AI

FAQ

How this task behaves

  • 01

    Does the AI check if the invoice actually exists in the SEFAZ database?

    No. This tool only checks the mathematical structure of the 44-digit key using Modulo 11.

  • 02

    Can the AI fix a typo in an invalid key?

    No. The AI only identifies if a key is valid or invalid. You must manually correct any errors.

  • 03

    What happens if I paste a key that is too short?

    The AI will flag it as an error because it doesn't meet the 44-digit requirement.

  • 04

    Can I upload a CSV file for validation?

    Yes, you can paste the contents of a CSV or a list of keys directly into the chat for the AI to process.

  • 05

    Does this tool change any data in my accounting software?

    No. This MCP is read-only. It performs calculations and reports results without touching your external systems.

  • More questions about NF-e Access Key Validator? The Connector page answers them. See everything the NF-e Access Key Validator Connector can do

Connect NF-e Validator to Claude, Cursor, ChatGPT & more