jetls-client

A VSCode client extension for JETLS.

JETLS is a new language server for Julia. JETLS aims to enhance developer productivity by providing advanced static analysis and seamless integration with the Julia runtime. By leveraging tooling technologies like JET.jl, JuliaSyntax.jl and JuliaLowering.jl, JETLS aims to offer enhanced language features such as type-sensitive diagnostic, macro-aware go-to definition and such.

[!note] JETLS.jl is not integrated with the julia-vscode extension yet. To use JETLS from VSCode, install this jetls-client extension. While we generally recommend disabling julia-vscode when using jetls-client, this is not required; you can use both julia-vscode and jetls-client in the same VSCode session. However, since the LSP features provided by JETLS.jl differ in both type and quality from those provided by julia-vscode's language server backend (LanguageServer.jl), you may encounter confusing situations where, for example, completion candidates are provided from different backends.

Requirements

VSCode v1.96.0 or higher
Julia v"1.12" or higher (1.12.2+ recommended)

Installation

[!warning] The jetls-client extension does not bundle JETLS.jl itself. You need to install the jetls executable separately before using the extension.

Install the jetls executable app, which is the main entry point for running JETLS:
```
julia -e 'using Pkg; Pkg.Apps.add(; url="https://github.com/aviatesk/JETLS.jl", rev="release")'
```
This will install the jetls executable to ~/.julia/bin/.
Make sure ~/.julia/bin is available on the PATH environment so the jetls executable is accessible. You can verify the installation by running:
```
jetls --help
```
If this displays the help message, the installation was successful and ~/.julia/bin is properly added to your PATH.
Install jetls-client:
- Open VSCode
- Go to Extensions (Invoke the View: Show Extensions command)
- Search for "JETLS Client"
- Click Install
Open any Julia file

The extension will automatically use the jetls executable from your PATH.

[!note] To update JETLS to the latest version, re-run the installation command:
julia -e 'using Pkg; Pkg.Apps.add(; url="https://github.com/aviatesk/JETLS.jl", rev="release")'
To pin a specific version instead, use the release tag rev="YYYY-MM-DD":
julia -e 'using Pkg; Pkg.Apps.add(; url="https://github.com/aviatesk/JETLS.jl", rev="2025-11-25")'

Launching configuration (advanced)

Most users do not need any further configuration beyond the installation steps above. The following settings are available for advanced use cases.

Executable configuration

Configure the JETLS executable through the jetls-client.executable setting:

Object form {"path": string, "threads": string}: Customize the executable path or thread setting (default: {"path": "jetls", "threads": "auto"})
Array form string[]: Use a local JETLS checkout for development, e.g, (["julia", "--startup-file=no", "--history-file=no", "--project=/path/to/JETLS", "-m", "JETLS"])

Communication channel

The extension automatically selects the most appropriate communication channel based on your environment:

Local development: pipe - Complete isolation from stdin/stdout, fastest for local communication
Remote SSH/WSL: pipe - Works transparently across remote connections
Dev Containers: stdio - Maximum compatibility for containerized environments

For most users, this automatic selection provides optimal performance and reliability without requiring manual configuration.

You can override the automatic selection using "jetls-client.communicationChannel": string:

"auto" (default): Automatic selection as described above
"pipe": Uses Unix domain socket/named pipe
"socket": Uses TCP socket (configure port with "jetls-client.socketPort": number, default 0 for auto-assign)
"stdio": Uses standard input/output

For detailed information about each communication channel and when to use them, see the Communication channels documentation.

Initialization options

Static options that are sent to JETLS during startup can be configured through VSCode's settings.json file using the "jetls-client.initializationOptions" section. These settings require a server restart to take effect.

For detailed initialization options and examples, see the Initialization options documentation.

Example initialization options

{
  "jetls-client.initializationOptions": {
    "n_analysis_workers": 2
  }
}

Configuring JETLS

JETLS behavior (diagnostics, formatting, etc.) can be configured through VSCode's settings.json file using the jetls-client.settings section.

For detailed configuration options and examples, see the Configuration documentation.

Example configuration

.vscode/settings.json

{
  "jetls-client.settings": {
    "full_analysis": {
      "debounce": 2.0
    },
    // Use JuliaFormatter instead of Runic
    "formatter": "JuliaFormatter",
    "diagnostic": {
      "patterns": [
        // Suppress toplevel/inference warnings in test folder
        {
          "pattern": "(toplevel|inference)/.*",
          "match_by": "code",
          "match_type": "regex",
          "severity": "off",
          "path": "test/**/*.jl"
        }
      ]
    },
    "testrunner": {
      "executable": "/path/to/custom/testrunner"
    }
  }
}

License

MIT License. See LICENSE.md for details.

JETLS Client

aviatesk