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Tool Blocking Feature Example

This example demonstrates how to use the blockedTools feature to prevent specific tools from being executed on external MCP servers.

Example Configuration​

Create or update your .mcp-config.json file:

{
  "mcpServers": {
    "filesystem": {
      "name": "filesystem",
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "."],
      "transport": "stdio",
      "blockedTools": ["move_file", "delete_file", "remove_directory"]
    },
    "github": {
      "name": "github",
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "transport": "stdio",
      "env": {
        "GITHUB_PERSONAL_ACCESS_TOKEN": "your_token_here"
      },
      "blockedTools": ["delete_repository", "transfer_repository"]
    },
    "bitbucket": {
      "name": "bitbucket",
      "command": "npx",
      "args": ["-y", "@nexus2520/bitbucket-mcp-server"],
      "transport": "stdio",
      "env": {
        "BITBUCKET_USERNAME": "your-bitbucket-username",
        "BITBUCKET_APP_PASSWORD": "your-app-password"
      },
      "blockedTools": ["delete_repository", "delete_branch"]
    }
  }
}

Testing the Feature​

1. Load the Configuration​

import { NeuroLink } from "@juspay/neurolink";

const neurolink = new NeuroLink();

// Load external servers from configuration
await neurolink.loadExternalMCPServers("./.mcp-config.json");

2. List Available Tools​

// Get MCP status to see loaded servers
const status = await neurolink.getMCPStatus();
console.log(`Loaded ${status.totalServers} servers`);

// List all available tools (blocked tools won't appear here)
const tools = await neurolink.listMCPTools();
console.log(
  "Available tools:",
  tools.map((t) => t.name),
);

3. Attempt to Execute a Blocked Tool​

try {
  // This will fail because 'delete_file' is blocked
  await neurolink.executeMCPTool("filesystem.delete_file", {
    path: "/some/file.txt",
  });
} catch (error) {
  console.error("Expected error:", error.message);
  // Output: "Tool 'delete_file' is blocked on server 'filesystem' by configuration"
}

4. Execute an Allowed Tool​

// This will succeed because 'read_file' is not blocked
const content = await neurolink.executeMCPTool("filesystem.read_file", {
  path: "/some/file.txt",
});
console.log("File content:", content);

Use Cases​

1. Production Safety​

Block destructive operations in production:

{
  "mcpServers": {
    "filesystem-prod": {
      "blockedTools": [
        "delete_file",
        "remove_directory",
        "move_file",
        "write_file"
      ]
    }
  }
}

2. Read-Only GitHub Access​

Allow read operations but block writes:

{
  "mcpServers": {
    "github-readonly": {
      "blockedTools": [
        "create_repository",
        "delete_repository",
        "create_issue",
        "close_issue",
        "create_pull_request",
        "merge_pull_request"
      ]
    }
  }
}

3. Compliance and Audit​

Block sensitive operations that require audit trails:

{
  "mcpServers": {
    "database": {
      "blockedTools": [
        "drop_table",
        "truncate_table",
        "delete_all_records",
        "update_schema"
      ]
    }
  }
}

Verification​

Run tests to verify the feature works correctly:

# Run the blocklist tests
pnpm test test/unit/mcp/externalServerBlocklist.test.ts

# Or run all tests
pnpm test

Notes​

  • Blocked tools are filtered during discovery, so they won't appear in the list of available tools
  • Attempts to execute blocked tools will throw an error with a clear message
  • The blockedTools array can be empty or omitted if no tools need to be blocked
  • Tool names are case-sensitive and must match exactly