Agentic Brownfield Coding (ABC)

This Claude Code plugin repo assists complex software projects in their first steps towards agentic coding:

1. Scaffolding and gradually augmenting an existing codebase with an efficient harness setup.
2. Learning controlled agentic development workflows with a human-in-the-loop mindset.

Background

The ABC project arose from a dissatisfaction with the built-in /init command of Claude Code, which tries to derive agent instructions by scanning the existing repository content. Especially for large and complex codebases, this approach generally leads to poor results, as summarized comprehensively by Google engineer Addy Osmani.

Another major inspiration was Dexter Horthy's work on AI in Complex Codebases which has become known for the RPI workflow. Together with co-founder Kyle Mistele, he promotes disciplined harness engineering and controlled interactive workflows to rein in the non-determinism of coding agents.

Details about the concrete hypotheses and design philosophy behind the ABC solutions can be found in the full length background essay.

System Requirements

• Linux — natively supported, requires jq installed
• macOS — supported (agent will substitute GNU-only utilities), requires jq installed
• Windows — requires Git Bash and jq on PATH

Installation

claude plugin marketplace add ralfstrobel/agentic-brownfield-coding

claude plugin install abc-init@agentic-brownfield-coding
claude plugin install abc@agentic-brownfield-coding

[!TIP] The separate init plugin is only required once for scaffolding and can be uninstalled after.

Uninstallation

claude plugin uninstall abc-init@agentic-brownfield-coding
claude plugin uninstall abc@agentic-brownfield-coding

claude plugin marketplace remove agentic-brownfield-coding

Usage

Scaffolding

These commands should be run using Fable or Opus as they require complex codebase reasoning.

• /abc-init:standalone – Create initial Claude Code artifacts for single-application projects.

• /abc-init:monorepo – Create initial Claude Code artifacts for monorepo projects (multiple sub-projects/teams).

• /abc-init:bashless – (Optional) Create MCP tool wrappers for relevant CLI commands and disable the Bash tool, in order to prevent inefficient tool choice and harness bypassing via shell. While highly beneficial to enforce strictly controlled agentic workflows, projects should be aware that this introduces increased harness engineering overhead to curate and debug the custom toolset.

• /abc-init:headless – (Optional) Scaffold a driver script for batch execution of headless agent micro-sessions (repetitive file migrations, doc generation, component analysis...).