JacHacks: Build an AI Agent in 30 Minutes

Learn the 4 core patterns of agentic AI — and build a working Hackathon Pitch Builder agent along the way.

This repo also doubles as a reference for AI coding assistants working on Jac projects. See CLAUDE.md for the full patterns guide.

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What We're Building

A Hackathon Pitch Builder: you give it your interests and skills, and it brainstorms ideas, structures a pitch, researches similar projects, and routes you to the right domain mentor — all autonomously.

We build it in 4 steps, one pattern per step:

Step	Pattern	File
1	Generate — by llm() free-form output	step1_generate.jac
2	Extract — by llm() with a typed obj return	step2_extract.jac
3	Invoke — by llm(tools=[...]) with ReAct tool calling	step3_invoke.jac
4	Route — walker visits LLM-chosen nodes in parallel	step4_route.jac

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Setup

# 1. Install the Jac runtime
pip install jaseci

# 2. Set your OpenAI API key (you'll get one at the start of the session)
export OPENAI_API_KEY="your-key-here"

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Follow Along

Run each step standalone — no UI, just the pattern in isolation:

jac run step1_generate.jac
jac run step2_extract.jac
jac run step3_invoke.jac
jac run step4_route.jac

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Build It Yourself: app_tutorial.jac

app_tutorial.jac is the full app scaffold with the four HTTP endpoints stubbed as TODO placeholders. Each one is a walker:pub — Jac auto-generates the REST endpoint when you run jac start.

Your job: fill in the four walkers so the React frontend can call them.

walker:pub run_brainstorm {
    # has interests: str;
    # has skills: str;
    # can do with Root entry {
    #     report brainstorm_ideas(self.interests, self.skills);
    # }
}

Each TODO comment tells you which fields the frontend sends, which pattern to call, and what to report. When all four are filled in:

jac start app_tutorial.jac
# open http://localhost:8000

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Run the Finished App

The completed version is in app.jac:

jac start app.jac
# open http://localhost:8000

All 4 steps wired together in the browser — each step unlocks when the previous one completes.

Frontend files:

frontend/
├── App.cl.jac     ← main layout + state management
├── Step1.cl.jac   ← Generate: brainstorm form
├── Step2.cl.jac   ← Extract: structured pitch cards
├── Step3.cl.jac   ← Invoke: research + GitHub results
├── Step4.cl.jac   ← Route: mentor advice
└── styles.css     ← dark hackathon theme

The frontend calls each walker with:

result = root spawn run_brainstorm(interests=interests, skills=skills);
ideas  = result.reports[0];

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Resources

• Jac docs: https://docs.jaseci.org
• Jaseci GitHub: https://github.com/Jaseci-Labs/jaseci
• JacHacks: https://jachacks.org
• Community Discord: https://discord.gg/6j3QNdtcN6