Creating an Agent

Overview

Creating a custom agent lets you define a specialized environment for a specific type of work. A Rust agent includes the Rust toolchain. A Python data science agent includes Jupyter, pandas, and scipy. You define the tools — jackin’ handles the rest.

Step by step

1. Create a GitHub repository

   Name it jackin-{your-agent-name}. For example, jackin-rustacean for a Rust-focused agent.

2. Create the manifest file

   jackin.agent.toml

   dockerfile = "Dockerfile"
   
   [claude]
   plugins = []
   
   [identity]
   name = "Rustacean"

3. Create the Dockerfile

   Dockerfile

   FROM projectjackin/construct:trixie
   
   # Install Rust via mise
   RUN mise install rust@stable && mise use --global rust@stable
   
   # Install additional Rust tools
   RUN cargo install cargo-nextest cargo-watch

4. Push to GitHub

   git add -A && git commit -m "Initial agent setup"
   git push origin main

5. Load your agent

   jackin load rustacean

Dockerfile guidelines

The construct base is required

Your final stage must start from the construct image:

FROM projectjackin/construct:trixie

Caution

This is the literal string jackin’ checks for. FROM projectjackin/construct:latest or any other tag will fail validation.

Multi-stage builds are supported

Use earlier stages for compilation or asset preparation:

# Build stage — use any base image
FROM rust:1.87-slim AS builder
WORKDIR /build
COPY tools/ .
RUN cargo build --release

# Final stage — must use the construct
FROM projectjackin/construct:trixie
COPY --from=builder /build/target/release/my-tool /usr/local/bin/

Use mise for language management

The construct ships with mise — a polyglot version manager. Use it to install languages:

Node.js

RUN mise install node@22 && mise use --global node@22

# Python
RUN mise install python@3.12 && mise use --global python@3.12

# Go
RUN mise install go@1.23 && mise use --global go@1.23

# Multiple languages
RUN mise install node@22 python@3.12 go@1.23 && \
    mise use --global node@22 python@3.12 go@1.23

Install packages as the claude user

The construct switches to the claude user. Your Dockerfile commands run as that user. If you need root access:

USER root
RUN apt-get update && apt-get install -y some-package
USER claude

Claude plugins

Agent repos can declare Claude Code plugins to install. Add them to the [claude] section in your manifest:

jackin.agent.toml

dockerfile = "Dockerfile"

[claude]
plugins = ["code-review@claude-plugins-official"]

[identity]
name = "My Agent"

These plugin IDs are written into the agent’s runtime state and installed automatically when the container starts.

Testing your agent

The fastest way to test is to load it:

jackin load your-agent-name --rebuild

The --rebuild flag forces a fresh image build, picking up any Dockerfile changes.

Use --debug to see raw Docker output if something goes wrong:

jackin load your-agent-name --rebuild --debug

Example agents

Agent	Purpose	Repository
Agent Smith	Default general-purpose agent	donbeave/jackin-agent-smith
The Architect	Rust development (used for jackin’ itself)	donbeave/jackin-the-architect

These repos are good starting points when creating your own agent. Agent Smith is intentionally minimal, while The Architect shows a more involved setup with Rust tooling and build dependencies.