| title | SQL Server Express LocalDB | |||||
|---|---|---|---|---|---|---|
| description | Become familiar with SQL Server Express LocalDB. Developers can use this lightweight Database Engine for writing and testing Transact-SQL code. | |||||
| author | rwestMSFT | |||||
| ms.author | randolphwest | |||||
| ms.date | 03/23/2026 | |||||
| ms.service | sql | |||||
| ms.subservice | configuration | |||||
| ms.topic | concept-article | |||||
| ms.custom |
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| helpviewer_keywords |
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| ai-usage | ai-assisted |
[!INCLUDE SQL Server]
Microsoft SQL Server Express LocalDB is a feature of [!INCLUDE ssexpress-md] targeted to developers. In [!INCLUDE sssql25-md] and later versions, LocalDB is included with [!INCLUDE ssnoversion-md] Express edition. In [!INCLUDE sssql22-md] and earlier versions, LocalDB is available on SQL Server Express edition with Advanced Services.
LocalDB installation copies a minimal set of files necessary to start the [!INCLUDE ssDEnoversion]. After LocalDB is installed, you can initiate a connection using a special connection string. When you connect, the necessary [!INCLUDE ssNoVersion] infrastructure is automatically created and started, enabling the application to use the database without complex configuration tasks. Developer Tools can provide developers with a [!INCLUDE ssDEnoversion] that lets them write and test [!INCLUDE tsql] code without having to manage a full server instance of [!INCLUDE ssNoVersion].
LocalDB is a feature you select during SQL Server Express installation, and is available when you download the media. For [!INCLUDE sssql25-md] and later versions, LocalDB is included with the Express edition download. For [!INCLUDE sssql22-md] and earlier versions, the edition is called Express Advanced, and you can choose either that or the standalone LocalDB package when downloading.
- SQL Server 2025 Express edition
- SQL Server 2022 Express edition
- SQL Server 2019 Express edition
- SQL Server 2017 Express edition
- SQL Server 2016 Express edition
The LocalDB installer SqlLocalDB.msi is available in the installation media for all editions except for Express Core. It's located in the <installation_media_root>\<LCID>_ENU_LP\x64\Setup\x64 folder. LCID is a locale identifier or language code. For example, an LCID value of 1033 refers to the en-US locale.
Alternatively, you can install LocalDB through the Visual Studio Installer, as part of the Data Storage and Processing workload, the ASP.NET and web development workload, or as an individual component.
Install LocalDB through the installation wizard or by using the SqlLocalDB.msi program. LocalDB is an option when installing SQL Server Express LocalDB.
Select LocalDB on the Feature Selection/Shared Features page during installation. There can be only one installation of the LocalDB binary files for each major [!INCLUDE ssDEnoversion] version. Multiple [!INCLUDE ssDE] processes can be started, and all use the same binaries. An instance of the [!INCLUDE ssDEnoversion] started as the LocalDB has the same limitations as [!INCLUDE ssExpress].
An instance of [!INCLUDE ssExpress] LocalDB is managed by using the SqlLocalDB.exe utility. [!INCLUDE ssExpress] LocalDB should be used in place of the [!INCLUDE ssExpress] user instance feature, which was deprecated.
The LocalDB setup program uses the SqlLocalDB.msi program to install the necessary files on the computer. After it's installed, LocalDB is an instance of [!INCLUDE ssExpress] that can create and open [!INCLUDE ssNoVersion] databases. The system database files for the database are stored in the local AppData path, which is normally hidden. For example, %LOCALAPPDATA%\Microsoft\Microsoft SQL Server Local DB\Instances\LocalDBApp1\. User database files are stored where the user designates, typically somewhere in the %LOCALAPPDATA%\Microsoft\Microsoft SQL Server Local DB\Instances\<InstanceName> folder.
For more information about including LocalDB in an application, see [!INCLUDE vsprvs] Local Data Overview, Create a database and add tables in Visual Studio.
For more information about the LocalDB API, see SQL Server Express LocalDB reference.
The SqlLocalDB utility can create new instances of LocalDB, start and stop an instance of LocalDB, and includes options to help you manage LocalDB. For more information about the SqlLocalDB utility, see SqlLocalDB utility.
The instance collation for LocalDB is set to SQL_Latin1_General_CP1_CI_AS and can't be changed. Database-level, column-level, and expression-level collations are supported normally. Contained databases follow the metadata and tempdb collations rules defined by Contained database collations.
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LocalDB can't be managed remotely via SQL Server Management Studio.
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LocalDB can't be a merge replication subscriber.
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LocalDB doesn't support FILESTREAM.
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LocalDB only allows local queues for Service Broker.
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An instance of LocalDB owned by the built-in accounts such as
NT AUTHORITY\SYSTEMcan have manageability issues due to Windows file system redirection. Instead use a normal Windows account as the owner.
LocalDB supports two kinds of instances: automatic instances, and named instances. Different users of a computer can have instances with the same name. Each instance runs as the respective user in its own process.
Automatic instances of LocalDB are public. They're created and managed automatically for the user and can be used by any application. One automatic instance of LocalDB exists for every version of LocalDB installed on the user's computer. Automatic instances of LocalDB provide seamless instance management. There's no need to create the instance; it just works. This feature allows for easy application installation and migration to a different computer. If the target machine has the specified version of LocalDB installed, the automatic instance of LocalDB for that version is available on the target machine as well. Automatic instances of LocalDB have a special pattern for the instance name that belongs to a reserved namespace. Automatic instances prevent name conflicts with named instances of LocalDB. The name for the automatic instance is MSSQLLocalDB.
Named instances of LocalDB are private. They're owned by a single application that is responsible for creating and managing the instance. Named instances provide isolation from other instances and can improve performance by reducing resource contention with other database users. You must create named instances explicitly through the LocalDB management API, or implicitly via the app.config file for a managed application (although managed application might also use the API, if desired). Each named instance of LocalDB has an associated LocalDB version that points to the respective set of LocalDB binaries. The instance name of a LocalDB is sysname data type and can have up to 128 characters. (This instance name differs from regular named instances of [!INCLUDE ssNoVersion], which limits names to regular NetBIOS names of 15 ASCII characters.) The name of an instance of LocalDB can contain any Unicode characters that are legal within a filename. A named instance that uses an automatic instance name becomes an automatic instance.
To support scenarios where multiple users of the computer need to connect to a single instance of LocalDB, LocalDB supports instance sharing. An instance owner can choose to allow the other users on the computer to connect the instance. Both automatic and named instances of LocalDB can be shared. To share an instance of LocalDB, a user selects a shared name (alias) for it. Because the shared name is visible to all users of the computer, this shared name must be unique on the computer. The shared name for an instance of LocalDB has the same format as the named instance of LocalDB.
Only an administrator on the computer can create a shared instance of LocalDB. A shared instance of LocalDB can be unshared by an administrator or by the owner of the shared instance of LocalDB. To share and unshare an instance of LocalDB, use the LocalDBShareInstance and LocalDBUnShareInstance methods of the LocalDB API, or the share and unshare options of the SqlLocalDB utility.
This section describes how to connect to an automatic instance, a named instance, or a shared instance.
The easiest way to use LocalDB is to connect to the automatic instance owned by the current user by using the connection string Server=(localdb)\MSSQLLocalDB;Integrated Security=true. To connect to a specific database by using the file name, connect using a connection string similar to Server=(LocalDB)\MSSQLLocalDB;Integrated Security=true;AttachDbFileName=D:\Data\MyDB1.mdf.
Note
The first time a user on a computer tries to connect to LocalDB, the automatic instance must be both created and started. The extra time for the instance to be created can cause the connection attempt to fail with a timeout message. When this happens, wait a few seconds to let the creation process complete, and then connect again.
In addition to the automatic instance, LocalDB also supports named instances. Use the SqlLocalDB.exe program to create, start, and stop a named instance of LocalDB. For more information about SqlLocalDB.exe, see SqlLocalDB utility.
REM Create an instance of LocalDB
"C:\Program Files\Microsoft SQL Server\160\Tools\Binn\SqlLocalDB.exe" create LocalDBApp1
REM Start the instance of LocalDB
"C:\Program Files\Microsoft SQL Server\160\Tools\Binn\SqlLocalDB.exe" start LocalDBApp1
REM Gather information about the instance of LocalDB
"C:\Program Files\Microsoft SQL Server\160\Tools\Binn\SqlLocalDB.exe" info LocalDBApp1The last line in the previous code sample, returns information similar to the following table.
| Category | Value |
|---|---|
| Name | LocalDBApp1 |
| Version | <Current version> |
| Shared name | "" |
| Owner | <Your Windows user> |
| Auto create | No |
| State | Running |
| Last start time | <Date and time> |
| Instance pipe name | np:\\.\pipe\LOCALDB#F365A78E\tsql\query |
Note
If your application uses a version of .NET Framework before 4.0.2, you must connect directly to the named pipe of the LocalDB. The Instance pipe name value is the named pipe that the instance of LocalDB is listening on. The portion of the Instance pipe name after LOCALDB# will change each time the instance of LocalDB is started. To connect to the instance of LocalDB by using [!INCLUDE ssManStudioFull], type the instance pipe name in the Server name box of the Connect to Database Engine dialog box. From your custom program you can establish connection to the instance of LocalDB using a connection string similar to SqlConnection conn = new SqlConnection(@"Server=np:\\.\pipe\LOCALDB#F365A78E\tsql\query");
To connect to a shared instance of LocalDB, add \.\ (backslash + dot + backslash) to the connection string to reference the namespace reserved for shared instances. For example, to connect to a shared instance of LocalDB named AppData, use a connection string such as (localdb)\.\AppData as part of the connection string. A user connecting to a shared instance of LocalDB that they don't own must have a Windows Authentication or [!INCLUDE ssNoVersion] Authentication login.
LocalDB runs as a lightweight instance under the current user's context, which means most problems relate to instance state, file permissions, or version mismatches rather than server-level configuration. The following steps can help you diagnose and resolve the most common LocalDB problems.
Many common LocalDB problems are resolved by upgrading to the latest version of SQL Server Express. Download the latest version from the Installation media section, and install LocalDB. The newer version replaces the existing LocalDB binaries and includes fixes for known stability and compatibility problems.
After upgrading, delete and re-create your instances to use the updated binaries:
sqllocaldb stop MSSQLLocalDB
sqllocaldb delete MSSQLLocalDB
sqllocaldb create MSSQLLocalDB
sqllocaldb start MSSQLLocalDBCaution
Deleting an instance removes all databases associated with that instance. Back up any important data before you delete.
Run the following commands to confirm LocalDB is installed and check the state of your instance:
sqllocaldb info
sqllocaldb info MSSQLLocalDBThe first command lists all instances. The second command shows the version, owner, and state (Running or Stopped) of a specific instance. If sqllocaldb isn't recognized, LocalDB might not be installed or the installation path isn't in the system PATH variable.
To start an instance that isn't running:
sqllocaldb start MSSQLLocalDBLocalDB writes error logs to the user's AppData folder:
%LOCALAPPDATA%\Microsoft\Microsoft SQL Server Local DB\Instances\MSSQLLocalDB\error.log
Open this file in a text editor to check for specific error messages, startup failures, or configuration problems.
An instance of SQL Server Express LocalDB is an instance created by a user for their use. Any user on the computer can create a database using an instance of LocalDB, store files under their user profile, and run the process under their credentials. By default, access to the instance of LocalDB is limited to its owner. The data contained in the LocalDB is protected by file system access to the database files. If user database files are stored in a shared location, the database can be opened by anyone with file system access to that location, by using an instance of LocalDB that they own. If the database files are in a protected location, such as the users data folder, only that user, and any administrators with access to that folder, can open the database. The LocalDB files can only be opened by one instance of LocalDB at a time.
LocalDB always runs under the user's security context. LocalDB never runs with credentials from the local Administrators group. This means that all database files used by a LocalDB instance must be accessible using the owning user's Windows account, without considering membership in the local Administrators group.