arch github copilot: architecture and modernization plugin

Q: How to install arch in GitHub Copilot?

Run `copilot plugin install arch@awesome-copilot` in your terminal.

What arch does

The plugin adds the arch:doc-and-modernize skill to GitHub Copilot for inspecting checked-out repositories. In Documentation mode, it scans files on disk to build a single architecture reference. Every claim points directly to a file and line number. Unverified facts get flagged, while internal contradictions in code are resolved during analysis.

Modernization mode prepares an adaptive migration plan for legacy software. If an architecture document already exists, the plugin builds directly on it. Otherwise, it triggers Documentation mode first. The output includes per-feature migration notes, stack recommendations with ADRs, and a stepped implementation schedule.

This toolkit works local-first and treats remote API lookups as a flagged last resort. It is worth installing for code audits and developer onboarding. Without a local clone on disk, you cannot run it.

What it helps with

document system architecture with line-by-line file citations
map complex subsystems for onboarding incoming developers
prepare a phased legacy migration plan with stack recommendations and ADRs
identify and flag unverified architectural claims across local files

Example prompts for the agent

Analyze this local checkout and produce an architecture doc with file and line citations
Create a phased modernization plan and generate ADRs for the tech stack
Run arch:doc-and-modernize to document the repository before refactoring

How to install arch

Command from the source

copilot plugin install arch@awesome-copilot

From the same set554

The whole set →

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Questions about arch

How to install arch in GitHub Copilot?

Run copilot plugin install arch@awesome-copilot in your terminal.

What does arch:doc-and-modernize do?

It combines two workflows: writing a local-first architecture report with file citations and preparing an adaptive modernization plan.

What happens if an architecture document does not exist yet?

Modernization mode runs Documentation mode first to map the codebase, then proceeds with the migration plan.

Source text

arch · MIT

# Arch Plugin

Architecture and modernization toolkit for locally-cloned repositories. It produces a single, cited architecture document from the code on disk, and generates a phased modernization plan that automatically runs Documentation mode first when no architecture document exists yet.

## Installation

```bash
copilot plugin install arch@awesome-copilot
```

## What's Included

### Skills

- **`doc-and-modernize`** — Two complementary workflows for a locally-cloned repository, in one skill (installed via this plugin it surfaces as `arch:doc-and-modernize`):
- **Documentation mode** — Produce one comprehensive, verifiable architecture document for a repository you already have checked out locally. Works local-first (prefers the local checkout, treating remote/API lookups as a flagged last resort), cites every claim to a file + line, flags unverified facts, resolves contradictions, and deep-dives the most complex subsystems. Ideal for onboarding docs and system-design maps.
- **Modernization mode** — Generate a phased modernization plan for a legacy codebase. If a current architecture document exists it builds on it; otherwise it first runs the Documentation mode workflow to produce one, then continues to the plan. Produces per-feature migration docs, tech-stack recommendations with ADRs, and an adaptive, safety-laddered phased implementation plan.

## Source

This plugin is part of [Awesome Copilot](https://github.com/github/awesome-copilot).

## License

MIT

arch — GitHub Copilot plugin: what it does, how to install