Square

DataPublisher: Block

Route Square MCP traffic through Formal to control and log what AI agents do in Square:

Block tools you don’t want agents to call, such as create_customer.
Mask sensitive data in tool results, such as emails in list_customers responses.
Keep credentials at the Connector, so users and agents never see Square tokens.
Log every tool call with the user, the MCP client and its parameters.

0. Prepare your Connector

The Connector needs an MCP listener and a hostname with wildcard DNS and TLS. Set them up once by following Deploy the Connector. Every MCP server reuses them.

1. Add Square MCP server to your Resources

UI
Terraform
Pulumi
API

Open the Admin Catalog and click Add MCP.
Select the Square template.
Enter a DNS-label Name, such as square.
Choose the Space containing your Connector, such as default.
Configure upstream authentication as described below, then save.

If no Connector is in the selected Space, the Configuration tab shows MCP clients can’t connect directly yet. The reason reads: No Connector is in this server's Space.

Set space_id to the ID of the Space containing your Connector.

resource "formal_resource" "square" {
  name                    = "square"
  technology              = "mcp"
  hostname                = "mcp.squareup.com"
  space_id                = "<SPACE_ID>"
  native_users_v3_enabled = true
  port                    = 443
  tags = {
    "mcp-endpoint" = "/mcp"
  }
}

resource "formal_resource_oauth_settings" "square" {
  resource_id = formal_resource.square.id
}

Set spaceId to the ID of the Space containing your Connector.

import * as formal from "@formalco/pulumi";

const resource = new formal.Resource("mcp", {
  name: "square",
  technology: "mcp",
  hostname: "mcp.squareup.com",
  port: 443,
  spaceId: "<SPACE_ID>",
  tags: { "mcp-endpoint": "/mcp" },
  nativeUsersV3Enabled: true,
});

new formal.ResourceOauthSettings("mcpOAuth", {
  resourceId: resource.id,
});

Create a Resource with the MCP endpoint and its Space ID.

export FORMAL_API_KEY="<YOUR_API_KEY>"
RESOURCE_RESPONSE=$(curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.ResourceService/CreateResource \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @- <<JSON
  {
    "name": "square",
    "hostname": "mcp.squareup.com",
    "port": 443,
    "technology": "mcp",
    "spaceId": "<SPACE_ID>",
    "tags": [
      {
        "key": "mcp-endpoint",
        "value": "/mcp"
      }
    ]
  }
JSON
)
RESOURCE_ID=$(printf '%s' "${RESOURCE_RESPONSE}" | jq -r '.resource.id')
curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.ResourceService/CreateResourceOAuthSettings \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @- <<JSON
  {
    "resourceId": "${RESOURCE_ID}"
  }
JSON

2. Setup Authentication

Linked Accounts
Shared Credentials
Pass Through (Recommended)

Each user links their own Square account once in the Employee Catalog, and the Connector sends that user’s token to Square.

Linked Accounts selected under How does Formal authenticate to this resource?

Square only accepts MCP clients on its allowlist, and doesn’t let you register your own app for its MCP server.Linked Accounts isn’t available for Square. Use Pass Through instead.

3. Route Endpoint traffic

Auth is managed at the Connector level when you use Linked Accounts or Shared Credentials, so the Endpoint needs to forward the MCP traffic to it. Laptops and VMs with the Formal Endpoint keep using https://mcp.squareup.com/mcp, and a network rule sends that traffic to the Connector.

UI
Terraform
Pulumi
API

Go to Network Rules and create a rule named square-mcp.
Paste this expression, set the rule to Active, then save:

{
  "condition": {
    "pre_tcp": process.is_agent,
    // Every MCP server added to Formal: process.is_agent && resource.technology == "mcp"
    "pre_tls": process.is_agent && hostname == "mcp.squareup.com",
    "post_tls": true
  },
  "outputs": {
    "forward_to_connector": true
  }
}

resource "formal_network_rule" "square_mcp" {
  name        = "square-mcp"
  description = "Forward Square MCP traffic from agents to the Connector"
  status      = "active"

  # Every MCP server added to Formal: set pre_tls to process.is_agent && resource.technology == "mcp"
  cel_expression = <<-EOT
    {
      "condition": {
        "pre_tcp": process.is_agent,
        "pre_tls": process.is_agent && hostname == "mcp.squareup.com",
        "post_tls": true
      },
      "outputs": {
        "forward_to_connector": true
      }
    }
  EOT
}

import * as formal from "@formalco/pulumi";

new formal.NetworkRule("squareMcp", {
  name: "square-mcp",
  description: "Forward Square MCP traffic from agents to the Connector",
  status: "active",
  // Every MCP server added to Formal: set pre_tls to process.is_agent && resource.technology == "mcp"
  celExpression: `
    {
      "condition": {
        "pre_tcp": process.is_agent,
        "pre_tls": process.is_agent && hostname == "mcp.squareup.com",
        "post_tls": true
      },
      "outputs": {
        "forward_to_connector": true
      }
    }
  `,
});

export FORMAL_API_KEY="<YOUR_API_KEY>"
# Every MCP server added to Formal: set pre_tls to process.is_agent && resource.technology == "mcp"
CEL_EXPRESSION=$(cat <<'CEL'
{
  "condition": {
    "pre_tcp": process.is_agent,
    "pre_tls": process.is_agent && hostname == "mcp.squareup.com",
    "post_tls": true
  },
  "outputs": {
    "forward_to_connector": true
  }
}
CEL
)
jq -n --arg cel "${CEL_EXPRESSION}" '{
  name: "square-mcp",
  description: "Forward Square MCP traffic from agents to the Connector",
  status: "active",
  celExpression: $cel
}' | curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.DesktopService/CreateDesktopRoutingRule \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @-

The rule matches known agents only. See Identity headers.Cloud agents such as Claude, ChatGPT and Cursor Cloud Agents don’t run the Endpoint. Point them at this server’s Connector address, https://square.<connector-hostname>/mcp. Find it in the Admin Catalog: open Square, then copy Connector address on the Configuration tab.

4. Create policies

Tools

The Admin Catalog lists these tools for Square:

Tool	Description
`search_catalog_items`	Search Square catalog items.
`upsert_catalog_object`	Create or update a catalog object.
`list_customers`	List customers.
`create_customer`	Create a customer.
`list_orders`	List orders.
`create_order`	Create an order.
`list_payments`	List payments.
`create_payment`	Create a payment.
`refund_payment`	Refund a payment.
`list_locations`	List business locations.

Policies examples

Block a tool
Mask a tool's output

This policy blocks the tools that change data, so agents can only read Square.

package formal.v2

import future.keywords.if
import future.keywords.in

write_tools := {
  "upsert_catalog_object",
  "create_customer",
  "create_order",
  "create_payment",
  "refund_payment",
}

request := {
  "action": "block",
  "type": "block_with_custom_message",
  "message": "Writing to Square is not allowed.",
} if {
  input.resource.name == "square"
  input.mcp.method == "tools/call"
  input.mcp.tool_name in write_tools
}

This policy replaces email addresses in results returned by list_customers, list_orders, and list_payments.

package formal.v2

import future.keywords.if
import future.keywords.in

email_pattern := `[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}`

response := {
  "action": "rewrite",
  "body": regex.replace(input.http.body, email_pattern, "[REDACTED-EMAIL]"),
  "reason": "Mask emails in Square results",
} if {
  input.resource.name == "square"
  input.mcp.tool_name in {"list_customers", "list_orders", "list_payments"}
  regex.match(email_pattern, input.http.body)
}

See MCP resources for the input.mcp fields and Rewrite Action for body rewrites.

5. Check the logs

Open Logs and search for resource.name:square. Each Square tool call is one request log with the user, the MCP client and the tool. Open a log to see its tool parameters and the policies it triggered. A blocked write shows the block policy and its message. A masked search shows the rewrite policy.See Logs for search syntax and filters.

Troubleshooting

The agent says Square rejected your credentials

The agent relays: square rejected your credentials. Link or re-link your square account in Formal…Cause: Square no longer accepts the linked token, for example after the user revoked access in Square.Fix: Link Square again from the Employee Catalog.

Laptop traffic doesn't appear in Logs

Cause: The Endpoint isn’t running, or the network rule doesn’t match the client.Fix: Check the Endpoint is connected. The rule above only matches known agents. Other clients, such as a browser, reach Square directly unless the rule also matches them. See Network rules.

MCP clients can't connect directly yet

Cause: The Configuration tab lists the reason, most often No Connector is in this server's Space.Fix: Edit the server and choose the Space containing its Connector.

Getting Started

Example Use Cases

AI Governance

Configuring Formal

Integrations

Configuration

0. Prepare your Connector

1. Add Square MCP server to your Resources

2. Setup Authentication

3. Route Endpoint traffic

4. Create policies

Tools

Policies examples

5. Check the logs

Troubleshooting

Next Steps

MCP Gateway

All MCP servers

​0. Prepare your Connector

​1. Add Square MCP server to your Resources

​2. Setup Authentication

​3. Route Endpoint traffic

​4. Create policies

​Tools

​Policies examples

​5. Check the logs

​Troubleshooting

​Next Steps

MCP Gateway

All MCP servers

0. Prepare your Connector

1. Add Square MCP server to your Resources

2. Setup Authentication

3. Route Endpoint traffic

4. Create policies

Tools

Policies examples

5. Check the logs

Troubleshooting

Next Steps