Validate GST (Goods and Services Tax) Number from API Url using Regex in C#

Hi multidimitsof...,

Refer below sample code.

Namespaces

C#

using System.Text.RegularExpressions;
using System.Web;

VB.Net

Imports System.Text.RegularExpressions
Imports System.Web

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    Uri url = new Uri("https://api.mastergst.com/public/search?email=Multidimitsoftware%40gmail.com&gstin=33AAGCC7144L6ZE");
    string gstNo = HttpUtility.ParseQueryString(url.Query)["gstin"];
    Regex reg = new Regex("^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$");
    if (reg.IsMatch(gstNo))
    {
        ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Valid GST Number.');", true);
    }
    else
    {
        ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Invalid GST Number.');", true);
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    Dim url As Uri = New Uri("https://api.mastergst.com/public/search?email=Multidimitsoftware%40gmail.com&gstin=33AAGCC7144L6ZE")
    Dim gstNo As String = HttpUtility.ParseQueryString(url.Query)("gstin")
    Dim reg As Regex = New Regex("^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$")
    If reg.IsMatch(gstNo) Then
        ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('Valid GST Number.');", True)
    Else
        ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('Invalid GST Number.');", True)
    End If
End Sub

Screenshot