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Hello World#

Write and run your first Jac program in 2 minutes.

Your First Program#

Create a file named hello.jac:

with entry {
    print("Hello, World!");
}

Run it:

jac hello.jac

Output:

Hello, World!

Congratulations! You just wrote your first Jac program.

Understanding the Code#

with entry {
    print("Hello, World!");
}
Part Meaning
with entry The program's starting point (like main() in other languages)
{ } Code block (Jac uses braces, not indentation)
print() Built-in function to output text
; Statement terminator (required in Jac)

Run a Full-Stack App#

Want to go beyond a single file? Jac can scaffold a complete full-stack application in one command.

With the jac-client plugin installed, run:

jac create example --use fullstack
cd example
jac add
jac start main.jac

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

Run 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 add
jac start main.jac

Here are some jacpacks to try:

Jacpack Description
multi-user-todo-app Full-stack authenticated todo application
multi-user-todo-meals-app Todo app + AI meal planner powered by Jac's AI integration
AI_Study_Helper Educational platform with specialized AI agents
TasteTalk Restaurant feedback management system
jac-gpt Documentation assistant for the Jac language
jac-playground Browser-based Jac code editor
Algo Voice-enabled personal AI assistant

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 add
jac start main.jac

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

Next Steps#

Ready for something more substantial?