Config Schema Language (CSL)

CSL is a concise, type-safe language for describing configuration schemas. It blends familiar syntax (inspired by TypeScript/C++/Rust) with declarative validation, so teams can write readable schemas that IDEs and tooling can understand.

Highlights

• Human-friendly types: string, number, arrays (type[]), tables ({ ... }), unions ("dev" | "prod").
• Inline validation via annotations: @min(1), @regex("^[a-z]+$"), @format(email), etc.
• Constraint blocks for relationships: conflicts a with b;, requires a => b;, validate expr;.
• Wildcard keys and opaque types: *: for dynamic entries, any{} / any[] for passthrough areas.
• Language Server support (LSP) and Node/WASM builds for cross-platform usage.

Quick Taste

config AppConfig {
  app_name: string;
  environment: "dev" | "prod" = "dev";
  database: {
    host: string @format(url);
    port: number @range(1024, 65535);
    ssl?: boolean;
  };

  constraints {
    conflicts database.ssl with insecure_mode;
    requires database.ssl => environment == "prod";
  };
}

Repository Layout

• impl/core/ — C++20 implementation: lexer, parser, language server, documentation generator.
• impl/node/ — NodeJS wrapper loading the WASM build for CLI/LSP.
• impl/extension/VSCode/ — VSCode extension wiring to the language server.
• impl/extension/IntelliJ/ — IntelliJ plugin wiring to the language server.
• docs/CSL.md — Complete language overview and reference.
• htdocs/ — Official site.

Build and Use

Prerequisites

• C++20 compiler (MSVC 2022+, Clang 12+, GCC 11+)
• CMake 3.12+

WebAssembly-specific

• Python 3.8+
• Emscripten SDK (will be automatically downloaded and setup by the build script)
• Ninja Build System (Windows-specific, will be automatically downloaded and setup by the build script)

Node Wrapper-specific

• Node.js 24.10.1+ (older versions may also work but not recommended)

VSCode Extension-specific

• Node.js 24.10.1+ (older versions may also work but not recommended)
• VS Code 1.106.1+ (older versions may also work but not recommended)

IntelliJ Plugin-specific

• JDK 25+ (older versions may also work but not recommended)
• Gradle
• IntelliJ IDEA 2025.2+ (older versions may also work but not recommended)

Native C++ binary

From the repository root:

cmake -B build -S impl/core -DCMAKE_BUILD_TYPE=Release
cmake --build build

This produces the csl and csl-test executable.

• Test a CSL file:

path/to/csl --test path/to/schema.csl

• Run the language server (choose one transport):

path/to/csl --langsvr --stdio
path/to/csl --langsvr --socket=8080
path/to/csl --langsvr --pipe=PipeName

• Run the full regression suite using the test runner:

# Linux / macOS (from build directory)
./csl-test --test ../tests

# Windows (from build directory)
.\Release\csl-test.exe --test ..\tests

WebAssembly + Node wrapper

Build the WASM artifacts and the Node wrapper:

# Build the WASM module
impl/core/BuildWasm Release

# Then compile the Node wrapper
cd impl/node
npm install
npm run compile

• Use the Node CLI wrapper (LSP/parse commands are forwarded to the WASM module):

node ./out/csl.js --test path/to/schema.csl
node ./out/csl.js --langsvr --stdio

VSCode extension

• Build the native csl binary (above) and place it under impl/extension/VSCode/core/.
• Install dependencies and compile the extension:

cd impl/extension/VSCode
npm install
vsce package

• This generates vsix package, which you can install in VSCode.

Documentation

• Full language specification: docs/CSL.md

Contributing

• Fork and create a feature branch.
• Keep changes aligned with the existing style.
• Add tests or examples where relevant and open a PR.

License

Apache License 2.0. See LICENSE.txt.