You can handle validation on the server-side as well and perform any custom logic. If, for some reason, the data submitted does not validate, you can use the JQGrid.ShowEditValidationMessage method - it will display validation error message on top of the dialog, e.g.

JQGrid1.ShowEditValidationMessage("'Integer' must be > 100");

for details, please refer to the ASPX and C# code-behind files.
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="default.aspx.cs" Inherits="JQSuiteASPNETExample.examples.editing_data.serverside_validation._default" %>
<%@ Register Assembly="Trirand.Web" TagPrefix="trirand" Namespace="Trirand.Web.UI.WebControls" %>

<!DOCTYPE html>
<html lang="en-us">
<head id="Head1" runat="server">
    <meta charset="utf-8">
    <title>jqGrid for ASP.NET WebForms - server side validation</title>
    <!-- The jQuery UI theme that will be used by the grid -->
    <link rel="stylesheet" type="text/css" media="screen" href="http://code.jquery.com/ui/1.12.1/themes/redmond/jquery-ui.css" />
    <!-- The jQuery UI theme extension jqGrid needs -->
    <link rel="stylesheet" type="text/css" media="screen" href="/themes/ui.jqgrid.css" />
    <!-- jQuery runtime minified -->
    <script src="/js/jquery-3.2.1.min.js" type="text/javascript"></script>
    <!-- The localization file we need, English in this case -->
    <script src="/js/trirand/i18n/grid.locale-en.js" type="text/javascript"></script>
    <!-- The jqGrid client-side javascript -->
    <script src="/js/trirand/jquery.jqGrid.min.js" type="text/javascript"></script>    
    
    <style type="text/css">
        body, html { font-size: 80%; }    
    </style>
</head>
<body>
    <form id="form1" runat="server">
    <div>       
       <trirand:JQGrid ID="JQGrid1" runat="server" Width="600px" 
            onrowediting="JQGrid1_RowEditing">         
            <Columns>
                <trirand:JQGridColumn DataField="ID" Editable="false" PrimaryKey="true" />
                <trirand:JQGridColumn DataField="Integer" Editable="true" />
                <trirand:JQGridColumn DataField="Number" Editable="true" />
                <trirand:JQGridColumn DataField="Email" Editable="true" />                
                <trirand:JQGridColumn DataField="Url" Editable="true" />                  
            </Columns>
            <ToolBarSettings ShowEditButton="true" />
            <EditDialogSettings CloseAfterEditing="true" Caption="Edit the selected row" />                        
       </trirand:JQGrid>
       
       <br /><br />
       <trirand:codetabs runat="server" id="DataTableCodeTabs"></trirand:codetabs>
       
    </div>
    </form>
</body>
</html>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using Trirand.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Text.RegularExpressions;

namespace JQSuiteASPNETExample.examples.editing_data.serverside_validation
{
    public partial class _default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (JQGrid1.AjaxCallBackMode == AjaxCallBackMode.RequestData)
            {
                JQGrid1.DataSource = GetData();
                JQGrid1.DataBind();
            }
        }

        protected void JQGrid1_RowEditing(object sender, Trirand.Web.UI.WebControls.JQGridRowEditEventArgs e)
        {    
            // valide the "Integer" edit field for Integer, Min(100) and Max(1000) values
            string intValue = e.RowData["Integer"];
            int integer;

            if (Int32.TryParse(intValue, out integer))
            {
                if (integer < 100)
                    JQGrid1.ShowEditValidationMessage("'Integer' must be > 100");
                if (integer > 1000)
                    JQGrid1.ShowEditValidationMessage("'Integer' must be < 1000");
            }
            else
            {
                JQGrid1.ShowEditValidationMessage("'Integer' requires integer values");
            }

            // valide the "Number" edit field for Decimal, Min(100.00) and Max(1000.00) values
            string numValue = e.RowData["Number"];
            decimal number;

            if (Decimal.TryParse(numValue, out number))
            {
                if (number < 100)
                    JQGrid1.ShowEditValidationMessage("'Number' must be > 100.00");
                if (number > 1000)
                    JQGrid1.ShowEditValidationMessage("'Number' must be < 1000.00");
            }
            else
            {
                JQGrid1.ShowEditValidationMessage("'Number' requires number values");
            }

            // validate the "Email" field for email validity
            string emailRegex = @"^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}" +
                                     @"\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\" +
                                     @".)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$";
            Regex re = new Regex(emailRegex);
            if (!re.IsMatch(e.RowData["Email"]))
                JQGrid1.ShowEditValidationMessage("'Email' is not in valid format.");


            // validate the "Url" field for URL validity
            string urlegex = "^(https?://)"
                    + "?(([0-9a-z_!~*'().&=+$%-]+: )?[0-9a-z_!~*'().&=+$%-]+@)?" //user@ 
                    + @"(([0-9]{1,3}\.){3}[0-9]{1,3}" // IP- 199.194.52.184 
                    + "|" // allows either IP or domain 
                    + @"([0-9a-z_!~*'()-]+\.)*" // tertiary domain(s)- www. 
                    + @"([0-9a-z][0-9a-z-]{0,61})?[0-9a-z]\." // second level domain 
                    + "[a-z]{2,6})" // first level domain- .com or .museum 
                    + "(:[0-9]{1,4})?" // port number- :80 
                    + "((/?)|" // a slash isn't required if there is no file name 
                    + "(/[0-9a-z_!~*'().;?:@&=+$,%#-]+)+/?)$";
            re = new Regex(urlegex);
            if (!re.IsMatch(e.RowData["Url"]))
                JQGrid1.ShowEditValidationMessage("'Url' is not in valid format.");


            DataTable dt = GetData();
            dt.PrimaryKey = new DataColumn[] { dt.Columns["ID"] };
            DataRow rowEdited = dt.Rows.Find(e.RowKey);

            rowEdited["Integer"] = integer;
            rowEdited["Number"] = number;
            rowEdited["Email"] = e.RowData["Email"];
            rowEdited["Url"] = e.RowData["Url"];

            JQGrid1.DataSource = GetData();
            JQGrid1.DataBind();
        }

        protected DataTable GetData()
        {
            if (Session["EditValidationData"] == null)
            {
                DataTable dt = new DataTable();
                dt.Columns.Add(new DataColumn("ID", typeof(int)));
                dt.Columns.Add(new DataColumn("Integer", typeof(int)));
                dt.Columns.Add(new DataColumn("Number", typeof(decimal)));
                dt.Columns.Add(new DataColumn("Email", typeof(string)));
                dt.Columns.Add(new DataColumn("Url", typeof(string)));

                dt.Rows.Add(new object[] { 1, "200000", "600000.34", "john.smith@yahoo.com", "http://www.yahoo.com" });
                dt.Rows.Add(new object[] { 2, "1600000", "7522100.21", "joe.woe@google.com", "http://www.google.com" });
                dt.Rows.Add(new object[] { 3, "430150", "6644060", "julia.bergman@bing.com", "http://www.bing.com" });
                dt.Rows.Add(new object[] { 4, "125330", "20040.99", "roy.corner@msn.com", "http://www.msn.com" });                

                Session["EditValidationData"] = dt;

                return dt;
            }
            else
            {
                return Session["EditValidationData"] as DataTable;
            }
        }
    }
}
Switch theme:


Theming is based on the very popular jQuery ThemeRoller standard. This is the same theming mechanism used by jQuery UI and is now a de-facto standard for jQuery based components. The benefits of using ThemeRoller are huge. We can offer a big set of ready to use themes created by professional designers, including Windows-like themes (Redmond), Apple-like theme (Cupertino), etc. In addition to that any jQuery UI controls on the same page will pick the same theme.

Last, but not least, you can always roll your own ThemeRoller theme, using the superb Theme Editor

To use a theme, simply reference 2 Css files in your Html <head> section - the ThemeRoller theme you wish to use, and the jqGrid own ThemeRoller Css file. For example (Redmond theme):

<link rel="stylesheet" type="text/css" media="screen" href="/themes/redmond/jquery-ui-1.8.2.custom.css" />
<link rel="stylesheet" type="text/css" media="screen" href="/themes/ui.jqgrid.css" />