QML Language Server Reference

QML Language Server is a tool shipped with Qt that helps you write code in your favorite (LSP-supporting) editor. See Language Server Protocol for more information.

Currently, it enables your editor to:

  • Autocomplete your code
  • Display qmllint warnings
  • Navigate to definitions in QML files
  • Find usages of JavaScript variables and QML objects
  • Rename JavaScript variables and QML objects
  • Format QML files

Note: qmlls is currently in development, see Known Limitations for more details.

Supported Features


QML Language Server can automatically lint opened QML files and display warnings or errors straight in the editor. See qmllint for more information about the linting process.


QML Language Server can format entire files from inside the editor. See qmlformat for more information about the formatting process.

Finding Definitions

QML Language Server can find definitions of JavaScript variables, functions, QML object id's and QML properties from their usages.

QML Language Server can also find the definition of types used in type annotations for JavaScript functions, QML object properties, and QML object instantiation.

Finding Usages

QML Language Server can find usages of JavaScript variables, QML object properties, JavaScript functions, QML object methods, and QML object id's.


QML Language Server can rename JavaScript variables and functions, as well as QML object properties, methods, and id's, as long as they are defined in a QML file.

Suggesting Autocompletion Items

QML Language Server provides autocompletion suggestions for JavaScript variables, expressions, and statements, as well as QML object properties, methods, and id's.

Tracking Changes in C++ Files

QML Language Server can track changes in C++ files defining QML types. It automatically rebuilds CMake QML modules to provide accurate and up-to-date warnings and completion items for C++ defined QML types.

You can disable this feature.

Setting up the QML Language Server in Your Editor

Note: You can find the QML Language Server binary under <Qt installation folder>/bin/qmlls in installations of Qt made with Qt Online Installer.

Setting up the Build Directory

QML Language Server needs to know the location of your build folder. You can pass it the following ways:

  • The --build-dir command line option. In this case your editor should invoke qmlls as following:
    <path/to/qmlls> --build-dir <path/to/build-directory>
  • The QMLLS_BUILD_DIRS environment variable.
  • The .qmlls.ini settings file, see Configuration File.

Note: When the build directory is specified in multiple ways, the command line option takes preference over the environment variable that takes precedence over the setting file.

Disabling Automatic CMake Builds

qmlls will try to trigger a CMake rebuild when it detects that the source code of a C++ defined QML type has been modified.

To disable this feature, use the following ways:

  • The --no-cmake-calls command line option. In this case your editor should invoke qmlls as follows:
    <path/to/qmlls> --build-dir <path/to/build-directory> --no-cmake-calls
  • The QMLLS_NO_CMAKE_CALLS environment variable.
  • The .qmlls.ini settings file, see Configuration File.

Configuration File

QML Language Server can be configured via a configuration file .qmlls.ini. This file should be in the root source directory of the project. It should be a text file in the ini-format.

Note: .qmlls.ini files can be generated automatically via QT_QML_GENERATE_QMLLS_INI.

The configuration file should look like this:

// .qmlls.ini

Currently, the configuration file can be used to set the build directory of the current project and optionally disable the automatic CMake rebuild functionality for C++ defined QML types.

Note: QML Language Server can create default configuration files using the --write-defaults option. This will overwrite an already existing .qmlls.ini file in the current directory.

Known Limitations

QML Language Server might emit false positive warnings on projects that were not built, as it needs the build information to find QML modules defined in the same project, for example.

Despite covering many common QML features, the QML Language Server is still in development with some features yet to be supported:

  • Renaming QML types.
  • Suggesting autocompletions on invalid QML files.
  • Navigating to definitions of objects defined in C++.
  • Supporting all QML and JavaScript language constructs for all features.

The QML code model in the QML Language Server does not yet support all of the JavaScript language constructs, which means that some features like navigating to definition and finding usages might not work on these language constructs.

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