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Installation and First Run#

Get Jac installed and ready to use in under 2 minutes.

Install Jac with a single command:

curl -fsSL https://raw.githubusercontent.com/jaseci-labs/jaseci/main/scripts/install.sh | bash

This downloads the self-contained native jac binary and puts it on your PATH. The binary bundles its own runtime, so no system Python, pip, or uv is required -- at install time or afterward.

Installer Options#

Pass flags after -- to customize the install:

Specific version:

curl -fsSL https://raw.githubusercontent.com/jaseci-labs/jaseci/main/scripts/install.sh | bash -s -- --version 2.3.1

Uninstall:

curl -fsSL https://raw.githubusercontent.com/jaseci-labs/jaseci/main/scripts/install.sh | bash -s -- --uninstall
Flag Description
--version V Install a specific release version
--uninstall Remove Jac

Upgrading#

Re-run the install command to upgrade to the latest version. The installer replaces the binary in place.

Built-in Subsystems & Optional Dependencies#

The jac binary bundles every capability -- the AI (byLLM), MCP, full-stack client, and deployment & scaling subsystems are all built in. There is nothing to enable; what jac install does is resolve a capability's optional third-party dependencies into your project:

# AI/LLM integration (byLLM is built in; this pulls its optional deps -- litellm, pillow, ...):
jac install byllm

# The MCP server and the production deployment & scaling subsystem ship built
# into the jac binary (no install): run `jac mcp`, and use `jac start` /
# `jac start --scale`. Scale's optional deps install per-project via jac.toml.

The MCP server for AI-assisted Jac development is built into the binary -- run jac mcp directly, no install needed (see Agent Skills and MCP).

jac install resolves packages from PyPI into your project environment; jaclang itself is provided by the binary, so it is never reinstalled. See One Binary, Build Anything for the full picture of what the binary bundles, and the CLI reference for all options.

Deployment & scaling is built in

Production serving and Kubernetes deployment (jac start, jac start --scale) ship inside the jac binary as the built-in scale subsystem -- there is no separate jac-scale package to install. Scale's optional heavier dependencies (MongoDB, Redis, Kubernetes, Prometheus, ...) are pulled into your project on demand: declare the matching [scale.*] config in jac.toml, then run jac install to resolve them into .jac/venv.

IDE Setup#

The Jac Language Support extension is available on both major extension marketplaces:

Marketplace Link
VS Code Marketplace jaseci-labs.jaclang-extension
Open VSX Registry jaseci-labs/jaclang-extension

Supported IDEs#

Install the Extension#

In any of the IDEs above, installing is the same:

  1. Open the Extensions panel - Ctrl+Shift+X / Cmd+Shift+X
  2. Search jaclang
  3. Click Install on "Jac Language Support" by Jaseci Labs

Manual Install (VSIX)#

For IDEs without marketplace access or for offline installs:

  1. Download the latest .vsix from GitHub Releases
  2. Open the Command Palette - Ctrl+Shift+P / Cmd+Shift+P
  3. Select "Extensions: Install from VSIX..."
  4. Choose the downloaded file

Extension Features#

  • Syntax highlighting for .jac files
  • Intelligent autocomplete
  • Real-time error detection
  • Hover documentation
  • Go to definition
  • Graph visualization

Verify Installation#

jac --version

Expected output:

   _
  (_) __ _  ___     Jac Language
  | |/ _` |/ __|
  | | (_| | (__     Version:  0.X.X
 _/ |\__,_|\___|    Python 3.12.3
|__/                Platform: Linux x86_64

📚 Documentation: https://docs.jaseci.org
💬 Community:     https://discord.gg/6j3QNdtcN6
🐛 Issues:        https://github.com/Jaseci-Labs/jaseci/issues

Run your first program to confirm everything works. Create hello.jac:

with entry {
    print("Hello from Jac!");
}

jac hello.jac

You should see Hello from Jac! printed to the console.

Scaffold a Full-Stack App#

The full-stack client framework ships with jaclang core, so you can scaffold a complete full-stack project in one command:

jac create example --use web-app
cd example
jac install
jac start

Note

main.jac is the default entry point. All jac start commands in this guide omit the filename. If your entry point has a different name (e.g., app.jac), pass it explicitly: jac start app.jac.

This creates a project with a Jac backend and a React frontend, ready to go at http://localhost:8000.

Community Jacpacks#

Jacpacks are ready-made Jac project templates you can spin up instantly. Since --use accepts a URL, you can run any jacpack directly from GitHub:

jac create my-todo --use https://raw.githubusercontent.com/jaseci-labs/jacpacks/main/multi-user-todo-app/multi-user-todo-app.jacpack
cd my-todo
jac install
jac start

Want to try one with AI built in? The multi-user-todo-meals-app uses Jac's AI integration features to generate smart shopping lists with costs and nutritional info. It works out of the box with an Anthropic API key:

export ANTHROPIC_API_KEY="your-key-here"
jac create meals-app --use https://raw.githubusercontent.com/jaseci-labs/jacpacks/main/multi-user-todo-meals-app/multi-user-todo-meals-app.jacpack
cd meals-app
jac install
jac start

To use any of the other jacpacks, just swap the URL:

jac create my-app --use https://raw.githubusercontent.com/jaseci-labs/jacpacks/main/<jacpack-name>/<jacpack-name>.jacpack

Upgrading Jac#

Re-run the one-line installer to upgrade the jac binary to the latest version:

curl -fsSL https://raw.githubusercontent.com/jaseci-labs/jaseci/main/scripts/install.sh | bash

Built-in subsystems (byLLM, MCP, scale) upgrade with the binary itself. To force-refresh a project's resolved dependencies, reinstall them:

jac install --force-reinstall

Creating a Project#

Use jac create to scaffold a new project:

# Client-only web app (no backend, runs in the browser)
jac create my-app --use web-static

# Start the development server
cd my-app
jac start

The --use web-static template sets up a complete project with:

  • main.jac -- Entry point with client code
  • jac.toml -- Project configuration
  • styles.css -- Default stylesheet
  • Bundled frontend dependencies (via Bun)

Available templates:

Template Command What It Creates
Web app --use web-app Full-stack web app with frontend and backend
Web static --use web-static Client-only app that runs in the browser (no backend)

You can also use community templates (Jacpacks):

jac create my-app --use <github-url>

For Contributors#

Building Jac from source uses ./scripts/fresh_env.sh, which builds the jac binary and puts it on your PATH. See the Contributing Guide for the full development setup.

Next Steps#