Data Product MCP Server: Reference

This article covers the MCP protocol objects exposed by each K2view Fabric Data Product: Resources, built-in and custom Tools, and Prompts.

MCP Resources

Resources expose LU table metadata. Use the resources/read method with fabric:// URIs:

Example request:

POST https://your-fabric-host.com/mcp/customer_bank/1
Content-Type: application/json

{
  "jsonrpc": "2.0",
  "id": 5,
  "method": "resources/read",
  "params": {
    "uri": "fabric://customer_bank/table/CCMS_Credit_Card_Payments"
  }
}

Example response (markdown format):

[
  {
    "uri": "fabric://customer_bank",
    "mimeType": "text/markdown",
    "text": "\tName: CCMS_CREDIT_CARD_PAYMENTS\n\n\tDescription: Tracks payments made towards credit card statements\n\n\tColumns:\n\t\t- [PK] PAYMENT_ID: INTEGER NOT NULL - Unique identifier for the payment\n\t\t- CARD_ID: INTEGER - Reference to the credit card for the payment\n\t\t..."
  }
]

Requesting a non-existent data product resource (e.g., fabric://invalid_name) returns a "Resource not found" error.

MCP Tools

Built-in Tools

Every data product MCP server includes the following built-in tools:

query

Execute custom SQL queries against the entity's MicroDB.

{"name": "query", "arguments": {"sqlQuery": "SELECT * FROM TAX_PAYMENTS"}}

Returns a JSON array of result rows. Returns an error message for syntax errors, missing tables, or empty sqlQuery.

readTable

Read rows from a specific table with optional filtering.

{"name": "readTable", "arguments": {"tableName": "ORDERS", "whereClause": "status='ACTIVE'", "fields": "order_id,amount", "limit": 100}}

describeTables

Describe table columns in the data product. At least one parameter must be provided.

{"name": "describeTables", "arguments": {"pattern": "CCMS%"}}

listTables

Get a list of all tables with their names and descriptions. No parameters required.

{"name": "listTables", "arguments": {}}

attach

Attach to a specific entity instance for subsequent data operations. When a URL already contains an IID, the URL IID takes precedence.

{"name": "attach", "arguments": {"iid": "1"}}

On success, the response includes:

• action: attached (new), updated (changed IID), or noop (URL IID takes precedence)
• previousIid: returned when updating from a previous IID

NOTE: If the MCP base URL includes an IID, it cannot be replaced during the session, as this would break the security restrictions intentionally set at the beginning of the session. In such a case you will get: "URL IID takes precedence over attach tool".

Session Variables

Session variables let an MCP client add parameters into a Fabric session that affect how LUI data is retrieved. They map directly to Fabric's native SET command mechanism, the same one used throughout Fabric to parameterize LU population logic, Broadway flows, and LU functions.

How they work

Before executing a query or readTable tool call, Fabric translates all stored session variables into SET commands and executes them on the Fabric session:

SET date_threshold = '2024-01-01'
SET currency = 'USD'

This runs before the GET command that loads the entity's MicroDB, so the data product's population logic can read those variables — for example, to filter records by date range, apply a currency, or scope results to a tenant.

Only query and readTable apply session variables before execution. Tools like listTables, describeTables, and attach do not.

How to set them

On any request that already carries a Mcp-Session-Id header (i.e., after the MCP session has been established), any URL query parameter — except token and iid — is automatically stored as a session variable:

POST /mcp/customer/123?date_threshold=2024-01-01&currency=USD
Mcp-Session-Id: <session-id>

Session variables persist for the duration of the session. To remove a variable, pass it again with an empty value.

Note: Query parameters on the initial initialize request (before a session ID has been issued) are not stored.

Broadway Flows as Custom Tools

Any Broadway flow can be exposed as an MCP tool by tagging it with the mcp-tool tag. When the LU is deployed, tagged flows are automatically registered with:

• Tool name derived from the flow name
• Input schema generated from the flow's parameters (externals)
• Description populated from the flow's metadata

Lifecycle:

• Adding the mcp-tool tag and deploying registers the flow
• Removing the tag and redeploying unregisters the flow
• On redeploy, new tagged flows are discovered dynamically

This enables extending the MCP server's capabilities with custom business logic — for example, a flow that calculates customer risk score or triggers a notification.

IID Usage:

If your Broadway flow tool requires a Fabric GET command to read or update the session's attached LUI, and therefore needs the IID, you must define an iid external to the flow. Fabric automatically and implicitly provides the IID to the tool flow, meaning the IID is not exposed as a tool argument. This preserves the high level of security and authorization for MCP calls.

MCP Prompts

Prompts provide guided workflows to MCP clients.

Built-in Prompts

queryAssistant prompt

The built-in queryAssistant prompt returns a comprehensive guide for interacting with the data product. It takes no arguments. Its content is generated dynamically on the server side from the current session context (data product name and attached IID):

{"promptName": "queryAssistant", "arguments": []}

The queryAssistant prompt includes:

• MicroDB explanation - How the Fabric MicroDB works (private SQLite database, data pre-scoped to the entity instance)
• Workflow guide - Step-by-step instructions: (1) discover tables with listTables, (2) query data with readTable or query, (3) use URL query parameters to pass session variables
• Best practices - When to use readTable vs. query, no need for entity ID filtering, using session variables
• Current context - The data product name and instance ID

Custom Prompts

Any Broadway flow can be exposed as an MCP prompt by tagging it with the mcp-prompt tag.

Their settings, lifecycle, and IID usage are similar to the custom tools described above.