What to use for MSSQL database connection string

An ASP.NET application on Windows hosting connects to its Microsoft SQL Server (MSSQL) database through a connection string. It holds four values: the database server, the database name, the database user and that user's password. This guide shows the correct syntax for modern .NET and for classic ASP.NET, where to find each value in Plesk, and how to fix the errors people hit most often.

1. The connection string, part by part

A SQL Server connection string is a list of key=value pairs separated by semicolons. Several keys have older synonyms, so you will see both forms in tutorials:

A complete example, with the placeholders in capitals replaced by your own values:

Server=YOUR_DB_HOST;Database=example_db;User ID=example_user;Password=YourStrongPassword;TrustServerCertificate=True;

Don't add Integrated Security=True or Trusted_Connection=True. Those use Windows authentication, and a hosting account signs in with a SQL Server user name and password instead.

2. Find the values in Plesk

For a walkthrough of creating the database, see Creating and managing MSSQL databases in Plesk.

3. ASP.NET Core and modern .NET

Store the string in appsettings.json:

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=YOUR_DB_HOST;Database=example_db;User ID=example_user;Password=YourStrongPassword;TrustServerCertificate=True;"
  }
}

Install the current SQL Server driver, Microsoft.Data.SqlClient (Entity Framework Core's SQL Server provider already includes it):

dotnet add package Microsoft.Data.SqlClient

Read the string by its name. With Entity Framework Core, in Program.cs:

builder.Services.AddDbContext<AppDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));

Or with plain ADO.NET:

using Microsoft.Data.SqlClient;

var connStr = builder.Configuration.GetConnectionString("DefaultConnection");
await using var conn = new SqlConnection(connStr);
await conn.OpenAsync();

System.Data.SqlClient, the driver in older tutorials, is deprecated. Use Microsoft.Data.SqlClient for new code.

4. ASP.NET Framework (web.config)

For an ASP.NET Framework site (Web Forms or MVC 5), put the string inside configuration in web.config:

<connectionStrings>
  <add name="DefaultConnection"
       connectionString="Server=YOUR_DB_HOST;Database=example_db;User ID=example_user;Password=YourStrongPassword;"
       providerName="System.Data.SqlClient" />
</connectionStrings>

Then read it in code by the same name:

using System.Configuration;

string connStr = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

The class is ConfigurationManager, not the long-obsolete ConfigurationSettings. The name in brackets must match the name attribute in web.config exactly; a mismatch gives a NullReferenceException when the page loads. Add a reference to System.Configuration if the compiler can't find ConfigurationManager.

Plesk lets you edit web.config in its File Manager, or you can publish it with Web Deploy along with the rest of your site.

5. Encryption and certificate errors

Since version 4.0, Microsoft.Data.SqlClient encrypts the connection by default and checks the server's certificate. If the certificate isn't trusted by the web server, the connection fails with:

A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - The certificate chain was issued by an authority that is not trusted.)

The usual fix is to add TrustServerCertificate=True; to the string. The connection stays encrypted; only the certificate check is skipped. For a database on the same hosting platform, this is the standard setting.

6. Connecting from your own computer

Plan for your application to reach the database from your hosting account, not from your PC. When we checked our Windows hosting server from outside on 23 September 2026, SQL Server's standard port was closed, so SQL Server Management Studio or Visual Studio on your computer can't be expected to connect.

Instead:

• manage tables and data from the database tools in Databases in Plesk;
• import and export with Plesk's Import Dump and Export Dump on the database;
• keep a separate local SQL Server (Express or Developer edition) for development, and use a different connection string on your PC.

Keep the two strings apart with appsettings.Development.json in .NET, or a web.config transform in ASP.NET Framework, so you never deploy your local string by mistake. If your project really needs remote access to the hosted database, ask support whether it can be arranged for your account.

7. Common errors and fixes

If the error isn't in this table, read Troubleshooting common ASP.NET issues, or open a ticket with the full error text (without your password).

8. Windows hosting at Domain India

Domain India's Windows hosting runs ASP.NET on IIS, managed with Plesk, and includes MSSQL databases: 1 on ASP Starter and 5 on ASP Business. Windows hosting has no SSH; you work through Plesk, FTP and Web Deploy. Prices on the cards are Domain India list prices, excluding 18% GST.

Stuck on a connection error? Our support team is on 24/7 live chat, and tickets get a first response within 15 minutes; resolution time depends on the issue. There is no phone support.

Frequently asked questions

Ready to run your ASP.NET application? Compare Windows hosting plans, read Creating and managing MSSQL databases in Plesk, or ask us in a support ticket.