archy 0.4.2

Architectural sensor for Python codebases

archy

Architectural sensor for Python codebases - keeps structure honest under AI-assisted development.

Status: v0.4.2. Usable today via:

Mode	Command
Inspection	archy graph, archy cycles
CI governance	archy check (reads archy.yaml)
One-shot score	archy score
Trended score	archy score --record + archy trend
MCP server	archy mcp

Benchmarks against pydantic, fastapi, flask, pytest, and archy-on-archy live in docs/CASE_STUDIES.md. Score design follows sentrux (modularity, acyclicity, depth, equality, geometric mean); see docs/LEARNINGS.md.

Why

AI agents generate code at machine speed. Without a feedback loop on structural health (module coupling, import cycles, layer violations), codebases drift architecturally even when every individual change looks fine in review.

archy watches a Python codebase, builds a live module-dependency graph, and surfaces drift through a single trended score plus a handful of actionable sub-metrics. It's designed to run in CI, in pre-commit, and as an MCP server (archy mcp) so coding agents can read their own architectural impact before committing.

Scope

• Python only. The cross-language story is deliberately someone else's problem.
• Tree-sitter powered. Robust to in-flight edits and partial files; survives syntax errors that would crash ast.
• Score that trends over time. A single number per commit, persisted, plotted. Trend matters more than the absolute value.
• Rules as YAML. "Layer X cannot import Y." No DSL, no plugins (yet).

Non-goals

• Multi-language analysis
• Replacing linters, type checkers, or test runners
• Generating code or auto-fixing violations

Quick start

uv sync

Inspect the graph

uv run archy graph path/to/project --internal-only
uv run archy graph path/to/project --format json > graph.json
uv run archy graph path/to/project --format dot | dot -Tsvg > graph.svg

Find import cycles

Tarjan SCCs of size >= 2. Use --strict in CI to fail on any cycle.

uv run archy cycles path/to/project
uv run archy cycles path/to/project --format json
uv run archy cycles path/to/project --strict

Enforce layer rules

Reads archy.yaml from the repo root. Exits 1 on any violation. See Layer rules below.

uv run archy check path/to/project
uv run archy check path/to/project --format json
uv run archy check path/to/project --config custom.yaml

Compute a quality score

Composite of modularity, acyclicity, depth, and equality (geometric mean).

uv run archy score path/to/project
uv run archy score path/to/project --format json

Track score over time

Persist per-commit scores to .archy/history.jsonl and chart the trend.

uv run archy score path/to/project --record
uv run archy trend path/to/project
uv run archy trend path/to/project --last 30 --format json

Regression gate

Fail if the current score drops more than --strict-tolerance (default 0.02) below the most recent recorded run.

uv run archy score path/to/project --strict
uv run archy score path/to/project --strict --record           # check then record
uv run archy score path/to/project --strict --strict-tolerance 0.0

Run as an MCP server

Stdio transport, so AI agents can call archy directly. See MCP server below.

uv run archy mcp

MCP server (archy mcp)

archy mcp exposes five tools to MCP-aware AI agents (Claude Code, the Anthropic API, etc.):

Tool	Purpose
archy_score	Compute the four-metric score; optional record=True and strict=True for the same regression-gate behaviour the CLI offers.
archy_cycles	Find import cycles.
archy_check	Run layer rules from archy.yaml.
archy_trend	Read recent score history.
archy_record_baseline	Convenience wrapper for archy_score(record=True); mirrors sentrux's session_start.

Wire it into Claude Code with this stanza in your config:

{
  "mcpServers": {
    "archy": { "command": "uv", "args": ["run", "archy", "mcp"] }
  }
}

Regression-gate semantics

--strict reads the last row from .archy/history.jsonl and compares the current score against it. Drops beyond the tolerance fail with exit code 1. The default tolerance (0.02) matches the threshold sentrux's gate uses. This gives archy parity with sentrux's regression-gate use case while keeping the long-term JSONL history for archy trend.

CI integration

GitHub Action

archy ships a composite action you can drop into any workflow:

- uses: hslee16/archy@v0.4.2
  with:
    command: score      # score | check | cycles
    path: .
    strict: "true"      # fail on regression (score) or any cycle (cycles)

Inputs (all optional unless noted):

Input	Default	Notes
command	score	score, check, or cycles
path	.	Project root to analyze
strict	true	score/cycles: fail on regression / any cycle
strict-tolerance	0.02	score --strict tolerance
record	false	score: append result to .archy/history.jsonl
config	(auto)	check: path to archy.yaml
python-version	3.10	Python to install

Pre-commit hook

Add to .pre-commit-config.yaml:

repos:
  - repo: https://github.com/hslee16/archy
    rev: v0.4.2
    hooks:
      - id: archy-check          # layer rules from archy.yaml
      - id: archy-score-strict   # regression gate against last recorded score
      - id: archy-cycles         # fail on any import cycle

archy-score-strict reads .archy/history.jsonl; commit a baseline first with archy score . --record.

Layer rules (archy check)

Drop an archy.yaml at the repo root declaring layers and forbidden directions:

layers:
  domain:
    modules:
      - "myapp.domain.**"
  application:
    modules:
      - "myapp.application.**"
  infra:
    modules:
      - "myapp.infra.**"
      - "myapp.adapters.**"

forbid:
  - {from: domain, to: application}
  - {from: domain, to: infra}
  - {from: application, to: infra}

Pattern syntax. Dotted-name globs: * matches one segment, ** matches zero or more. myapp.domain.** covers the package itself and every descendant. Modules must belong to at most one layer.

Discovery. archy check walks PATH upward to find archy.yaml unless --config is given. Exits 1 on violation.

archy enforces its own architecture this way; see archy.yaml at the repo root and the archy check . step in .github/workflows/ci.yml.

Development

uv sync                    # install runtime + dev deps from uv.lock
uv run ruff check          # lint
uv run ruff format         # format
uv run ty check            # type check
uv run pytest              # tests

Roadmap

Next up:

• archy_impact MCP tool: blast-radius analysis for a set of changed files
• archy graph MCP tool: expose the dep graph itself for agent-side reasoning
• Score deltas (archy_evolution): per-component diffs vs. the last recorded run
• Design Structure Matrix (archy dsm)

Shipped: tree-sitter import graph, __init__.py re-export resolution, Tarjan cycle detection, YAML layer rules (archy check), composite score (archy score), JSONL history + archy trend, MCP server (archy mcp), GitHub Action + pre-commit hooks.

See docs/FUTURE.md for the longer list and docs/LEARNINGS.md for design notes.

Contributing

See CONTRIBUTING.md for style rules. Notably: no em-dash characters (U+2014) anywhere in the repo.

License

MIT, see LICENSE.