How to Use Claude and ChatGPT Without Leaking Company Secrets

The Developer's Dilemma

You're debugging a production issue. The stack trace includes customer email addresses. The fastest solution? Paste it into Claude and ask for help.

But that customer data is now:

• Stored in Anthropic's systems
• Potentially used for training (depending on your plan)
• Visible to anyone with access to your chat history

77% of developers paste sensitive data into AI tools. Most don't realize the implications until it's too late.

The MCP Server Solution

The Model Context Protocol (MCP) Server acts as a transparent proxy between you and AI assistants. It:

1. Intercepts your prompts before they reach the AI
2. Detects and anonymizes PII automatically
3. Sends only anonymized data to the AI
4. De-anonymizes responses so you see original context

You interact with AI normally—the protection is invisible.

Setting Up MCP Server

Prerequisites

• Node.js 18+
• Claude Desktop, Cursor, or VS Code with Claude extension
• anonym.legal API key (get one free at anonym.legal/auth/signup)

Step 1: Get Your API Key

1. Sign up at anonym.legal/auth/signup
2. Navigate to Settings → API Tokens
3. Generate a new token
4. Copy the token (you'll only see it once)

Step 2: Configure Claude Desktop

Edit your Claude Desktop configuration file:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json Windows: %APPDATA%\Claude\claude_desktop_config.json Linux: ~/.config/Claude/claude_desktop_config.json

Add the anonym.legal MCP server:

{
  "mcpServers": {
    "anonym-legal": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-server-anonym-legal"],
      "env": {
        "ANONYM_API_KEY": "your-api-key-here"
      }
    }
  }
}

Step 3: Restart Claude Desktop

Close and reopen Claude Desktop. You should see "anonym-legal" in the MCP servers list.

Configuration for Cursor IDE

Cursor uses the same MCP protocol. Add to your Cursor settings:

{
  "mcp": {
    "servers": {
      "anonym-legal": {
        "command": "npx",
        "args": ["-y", "@anthropic/mcp-server-anonym-legal"],
        "env": {
          "ANONYM_API_KEY": "your-api-key-here"
        }
      }
    }
  }
}

What Gets Anonymized

The MCP Server detects and anonymizes 285+ entity types:

Example Transformation

Your prompt:

Debug this error from user john.smith@acme.com:
Error: Payment failed for card 4532-1234-5678-9012
Customer ID: CUST-12345
IP: 192.168.1.100

What Claude sees:

Debug this error from user [EMAIL_1]:
Error: Payment failed for card [CREDIT_CARD_1]
Customer ID: [CUSTOMER_ID_1]
IP: [IP_ADDRESS_1]

Claude's response (to you):

The error for john.smith@acme.com suggests the card
4532-1234-5678-9012 may have insufficient funds...

You see the original data; Claude only ever saw tokens.

Advanced Configuration

Custom Entity Types

Define additional patterns to detect:

{
  "mcpServers": {
    "anonym-legal": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-server-anonym-legal"],
      "env": {
        "ANONYM_API_KEY": "your-api-key",
        "CUSTOM_PATTERNS": "JIRA-[0-9]+,TICKET-[A-Z0-9]+"
      }
    }
  }
}

Allowlist Specific Data

Some data shouldn't be anonymized (public company names, product names):

{
  "env": {
    "ANONYM_API_KEY": "your-api-key",
    "ALLOWLIST": "Anthropic,Claude,anonym.legal"
  }
}

Disable Specific Entity Types

If you need certain types to pass through:

{
  "env": {
    "ANONYM_API_KEY": "your-api-key",
    "DISABLED_ENTITIES": "PHONE_NUMBER,URL"
  }
}

Verification

Test that anonymization is working:

1. Open Claude Desktop
2. Paste text with obvious PII: "Contact John Smith at john@example.com"
3. Check the MCP server logs (visible in Claude Desktop's developer tools)
4. The log should show: "Anonymized: 2 entities (PERSON, EMAIL_ADDRESS)"

Security Considerations

Where Processing Happens

The MCP server itself runs locally. Only the detection request (with hashed/anonymized data) goes to anonym.legal's API.

Data Retention

anonym.legal does not store your prompts or responses. The API:

• Receives text for analysis
• Returns entity positions
• Immediately discards the input

See our privacy policy for details.

Comparison: Without vs. With MCP Server

Pricing

MCP Server usage is included in all anonym.legal plans:

Most developers stay on Basic (€3/month) with typical usage.

Conclusion

AI assistants are essential for modern development, but they don't need to see your customers' data.

The MCP Server integration:

• Requires no workflow changes
• Protects PII automatically
• Works with Claude Desktop, Cursor, and VS Code
• Costs €3/month for most developers

Set it up once, and forget about it—your data is protected by default.

Get started:

• Sign up for free
• MCP Server documentation
• View all entity types

Sources:

• MCP Protocol Specification
• LayerX - 77% Developer AI Usage