Format of the initialization string does not conform to specification starting at index 0 in .net core code example

Example: argumentexception: format of the initialization string does not conform to specification starting at index 0.

Check your connection string. If you need help with it check Connection Strings, which has a list of commonly used ones.

Commonly used Connection Strings:

SQL Server 2012
Standard Security

Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;
Trusted Connection

Server=myServerAddress;Database=myDataBase;Trusted_Connection=True;
Connection to a SQL Server instance

The server/instance name syntax used in the server option is the same for all SQL Server connection strings.

Server=myServerName\myInstanceName;Database=myDataBase;User Id=myUsername;
Password=myPassword;
SQL Server 2005
Standard Security

Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;
Trusted Connection

Server=myServerAddress;Database=myDataBase;Trusted_Connection=True;
Connection to a SQL Server instance

The server/instance name syntax used in the server option is the same for all SQL Server connection strings.

Server=myServerName\myInstanceName;Database=myDataBase;User Id=myUsername;Password=myPassword;
MySQL
Standard

Server=myServerAddress;Database=myDataBase;Uid=myUsername;Pwd=myPassword;
Specifying TCP port

Server=myServerAddress;Port=1234;Database=myDataBase;Uid=myUsername;Pwd=myPassword;
Oracle
Using TNS

Data Source=TORCL;User Id=myUsername;Password=myPassword;
Using integrated security

Data Source=TORCL;Integrated Security=SSPI;
Using ODP.NET without tnsnames.ora

Data Source=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=MyHost)(PORT=MyPort)))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=MyOracleSID)));User Id=myUsername;Password=myPassword;