Language support

OpenIDEA describes every language in a small definition file, languages/<id>.toml. The definition says which files belong to the language, how to highlight them, and which language server and debug adapter provide code intelligence and debugging. Everything a language server offers (completion, navigation, diagnostics, refactorings) then works through the same editor features for every language.

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How language support works

Each open file gets its language from the definitions, checked in this order:

1. A per-file Override File Type (in the context menu of a file in the project tree or of an editor tab).
2. An exact file name (Dockerfile, go.mod) or a file name pattern.
3. The extension, longest match first (.html.erb before .erb).
4. The first line: a shebang such as #!/usr/bin/env python3, or a pattern such as <?php.
5. Otherwise the file is plain text.

You can add or remove file name patterns per language in Settings › Editor › File Types (Recognized File Types). For a recognized file, support comes in layers:

• Highlighting is instant: it comes from a CodeMirror mode in the editor, or from the bundled tree-sitter grammar when the language has no mode.
• Structure (outline, folding and the symbols in the project index) comes from a bundled tree-sitter grammar and needs no setup.
• Code intelligence comes from one or more language servers (LSP). The IDE starts them when you open a file, using the nearest folder that contains one of the server’s root markers (Cargo.toml, package.json, pom.xml, …) as the workspace root.
• Debugging comes from a debug adapter (DAP).

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Several servers for one language

A language can list more than one server:

• Alternatives (shown as a → b in the table below): only the first one that is installed runs. Python, for example, uses basedpyright, and falls back to pyright, ty or pyrefly only when basedpyright is missing. In Settings › Languages & Frameworks › Language Servers you can pick one of them or set the choice to Automatic (the first one available).
• Additions (shown as + b): run next to the main server, usually only in projects that use them. Ruff joins basedpyright in projects with a Ruff configuration; oxlint joins vtsls in projects with an oxlint configuration; the Angular and Laravel servers join in Angular and Laravel projects.

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Installing language servers and debuggers

OpenIDEA does not bundle language servers. When you open a file whose server is missing, a notification says that the server is not installed and offers Install, which installs it and restarts code insight for that language. You can also manage every tool on one page: The IDE never needs sudo. It installs tools into its own tools folder in the local data directory (see Data directories and logs), using the method that fits each tool: When the IDE looks for a server, it checks the executable you set in settings first, then its own tools folder, then your PATH. Servers that the IDE cannot install (for example sourcekit-lsp, which comes with the Swift toolchain, or the Godot editor’s own server) show an install hint instead.

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Configuring a server

Selecting a language server on the Language Servers page shows its settings, which are stored under languageServers.<name> in your settings (globally or per project):

• turn the server off, or choose which of several alternatives runs;
• Executable: the program to start;
• Startup: Arguments, Environment variables and Initialization options (changing these restarts the server);
• Workspace Configuration: the answer to the server’s workspace/configuration requests, applied without a restart.

Add Language Server… registers a server that no definition knows about: give its command, the languages it serves and its root markers.

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Support matrix

The table lists every built-in language definition. Server and debugger names in bold can be installed from the IDE; the others you install yourself (the install hint in the IDE says how). “Highlighting” and “Tree-sitter” mark instant highlighting and the bundled grammar for outline and folding. Notes:

• C, C++, Objective-C, Swift: lldb-dap comes with LLVM or Xcode. C and C++ can also be debugged with CodeLLDB or GDB 14+; see C and C++.
• Ruby: rdbg comes from the debug gem.
• GDScript: the language server and debugger are the Godot editor itself; see Godot.
• Arduino: needs Arduino IDE 2 (Arduino Language Server, Arduino CLI and clangd).
• Vue: the Vue server and vtsls run together; vtsls handles the TypeScript part.

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Run, test and debug

Run configurations are detected from the build files in your project. The table shows what is detected for each ecosystem; see Run configurations, Testing and Debugging for how to use them. Running, testing (with a test tree and Rerun Failed Tests) and debugging are tested end to end on sample projects for TypeScript, Python, Rust, Go, Java, Kotlin and PHP; debugging is also tested for C and C++. Code intelligence is tested with each of these languages’ real servers (TypeScript, Python, Rust, Go, Java, Kotlin, PHP).

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Changing or adding a language

• To change a built-in definition, put a file with the same id in the languages folder of the configuration directory; it replaces the built-in one at the next start. See Add a language for the format.
• Plugins can add languages, with their own servers and debuggers. See Language features.