SQL Server MCP

Instructions

Queries sys.databases to discover accessible databases. System databases
(master, tempdb, model, msdb) are excluded by default. Databases in the
blocklist (MSSQL_BLOCKED_DATABASES) are always excluded.

Args:
    include_system: If True, include system databases in the list

Returns:
    Dictionary with:
    - databases: List of available database names
    - current_database: The currently active database
    - count: Number of databases returned
    - blocked_count: Number of databases hidden due to blocklist

Implementation Reference

• src/mssql_mcp/tools/databases.py:15-80 (handler)

  The handler function for 'list_databases' tool. It queries sys.databases, filters out blocked and optional system databases, determines the current database, and returns a structured dictionary with the list and metadata. Registered via @mcp.tool() decorator.

  @mcp.tool()
  def list_databases(include_system: bool = False) -> dict[str, Any]:
      """List all available databases on the SQL Server.
  
      Queries sys.databases to discover accessible databases. System databases
      (master, tempdb, model, msdb) are excluded by default. Databases in the
      blocklist (MSSQL_BLOCKED_DATABASES) are always excluded.
  
      Args:
          include_system: If True, include system databases in the list
  
      Returns:
          Dictionary with:
          - databases: List of available database names
          - current_database: The currently active database
          - count: Number of databases returned
          - blocked_count: Number of databases hidden due to blocklist
      """
      try:
          manager = get_connection_manager()
          config = manager.config
          blocked_databases = config.blocked_databases
  
          # Query all databases
          query = """
              SELECT name, database_id, state_desc
              FROM sys.databases
              WHERE state_desc = 'ONLINE'
              ORDER BY name
          """
          rows = manager.execute_query(query)
  
          # Filter databases
          databases = []
          blocked_count = 0
  
          for row in rows:
              db_name = row["name"]
              db_name_lower = db_name.lower()
  
              # Check if blocked
              if db_name_lower in blocked_databases:
                  blocked_count += 1
                  continue
  
              # Check if system database
              if not include_system and db_name_lower in SYSTEM_DATABASES:
                  continue
  
              databases.append(db_name)
  
          # Get current database
          current_db_query = "SELECT DB_NAME() AS current_database"
          current_db_result = manager.execute_query(current_db_query)
          current_database = current_db_result[0]["current_database"] if current_db_result else None
  
          return {
              "databases": databases,
              "current_database": current_database,
              "count": len(databases),
              "blocked_count": blocked_count,
          }
  
      except Exception as e:
          logger.error(f"Error listing databases: {e}")
          return {"error": str(e)}

• src/mssql_mcp/tools/databases.py:11-13 (helper)

  Constant defining system databases excluded by default from the list.

  # System databases that are always excluded from listing
  SYSTEM_DATABASES = {"master", "tempdb", "model", "msdb"}

• src/mssql_mcp/tools/databases.py:17-32 (schema)

  Docstring defines the tool's input parameter (include_system: bool) and output schema (dict with databases list, current_database, count, blocked_count).

  """List all available databases on the SQL Server.
  
  Queries sys.databases to discover accessible databases. System databases
  (master, tempdb, model, msdb) are excluded by default. Databases in the
  blocklist (MSSQL_BLOCKED_DATABASES) are always excluded.
  
  Args:
      include_system: If True, include system databases in the list
  
  Returns:
      Dictionary with:
      - databases: List of available database names
      - current_database: The currently active database
      - count: Number of databases returned
      - blocked_count: Number of databases hidden due to blocklist
  """

• src/mssql_mcp/tools/databases.py:15-15 (registration)

  @mcp.tool() decorator registers the list_databases function as an MCP tool.

  @mcp.tool()