Setup Arch Unit

Setup Arch-Unit Architecture Tests

Instructions

Install and configure arch-unit-ts so that the project's module boundaries are enforced as part of the test suite, and wire a dedicated pre-commit hook that runs the architecture rules on every commit.

This skill is independent of setup-pre-commit: it manages its own block inside .husky/pre-commit (delimited by # >>> nexa arch-unit >>> markers) and does not touch any lint-staged configuration. Running both skills on the same project is safe.

Nexa Rules Gate

Read and follow ${CLAUDE_PLUGIN_ROOT}/shared/readiness/NEXA_RULES_GATE.md.

Prerequisites

The following must exist before running this skill:

• package.json — to determine the package manager and detect installed deps
• A Vitest setup — arch-unit-ts tests run as Vitest specs. If Vitest is not

installed, stop and tell the user to run /vitest-test first or install Vitest manually.

If package.json is missing or Vitest is not installed, stop and tell the user which prerequisite is missing.

DO NOT

• Do not skip the verification step (Step 8) — arch-unit-ts package matchers may

silently match zero files for folder names containing parens (route groups) or leading underscores (private folders). The sanity checks in the generated template catch this, but only if the spec is actually executed once.

• Do not modify or share configuration with the setup-pre-commit skill — this

skill manages its own labeled block inside .husky/pre-commit.

• Do not add the architecture spec to lint-staged — arch-unit-ts analyzes the

whole project, not the staged subset.

• Do not enable opt-in rule blocks (route groups, private folders, layered

architecture) without the user's explicit confirmation.

• Do not add a CI workflow — the user has explicitly scoped this skill to

pre-commit only.

• Do not invent package matcher patterns. Only use patterns from the

arch-unit-ts documentation, fetched via context7 in Step 0.

• Do not generate a spec that imports paths that don't exist in the project

(e.g. ..lib.. if there is no lib/ folder). Detect first, then write.

Step 0: Consult arch-unit-ts Documentation

Before writing any code, use the context7 MCP server to look up:

1. arch-unit-ts (library id /arch-unit-ts/arch-unit-ts) — confirm the

current API for:

• classes(), noClasses(), Architectures.layeredArchitecture()
• Package matchers: resideInAPackage, resideInAnyPackage,

resideOutsideOfPackage (if available)

• Dependency matchers: dependOnClassesThat, onlyDependOnClassesThat,

onlyHaveDependentClassesThat

• TypeScriptProject constructor signature and exclusion patterns
• filterClasses(glob) API for the fallback pattern
• TypeScriptClass.hasImport(name) and packagePath.getDotsPath()

1. arch-unit-ts version — read package.json after installation; the import

paths in the template (arch-unit-ts/dist/...) may differ across versions

If the API has changed since this skill was written, prefer what the documentation says for the installed version over what the template shows.

Workflow

Step 1: Gather Context

Detect the project layout. Read or run:

1. package.json — record:

• Whether arch-unit-ts is already a dep
• Whether husky is already a dep
• Whether Vitest is installed (look for vitest or @vitest/*)
• The package manager (presence of package-lock.json, pnpm-lock.yaml,

yarn.lock, bun.lockb)

1. Filesystem detection:

• Does src/ exist? If yes, the TypeScriptProject root is src. If no,

the root is ..

• Which of the common shared folders exist at the source root:

components/, lib/, hooks/, ui/, utils/, styles/?

• Does app/ exist? List immediate children matching (*)/ — these are

route groups.

• List immediate children of app/**/ matching _*/ — these are private

folders.

• Does any of these exist: domain/, application/, infrastructure/? If

yes, the layered-architecture opt-in is a strong candidate.

1. Existing test file check:

• Does tests/architecture/architecture.test.ts (or .spec.ts) already

exist? If yes, read it and ask the user whether to overwrite, extend, or skip — do not overwrite silently.

1. Existing Husky setup:

• Does .husky/ exist? Does .husky/pre-commit exist? If yes, read it and

check for an existing # >>> nexa arch-unit >>> block.

Record all findings before proceeding.

Step 2: Propose Default Rule Set

Present a single proposal to the user showing what the generated test will contain. Structure the message like this:

> Proposed architecture rules (based on the Next.js project structure > conventions and what I detected in your project): > > Enabled by default > - R1 — Shared code must not depend on app/ ([SHAREDDIRSLIST]) > Detected shared folders: [list]. app/ consumes them; reversing the > dependency would couple them to your routes. > > Opt-in (commented out in the generated file) > - R2 — Route groups must not cross-import [only show if route groups > detected: list them, e.g. (marketing), (shop)] > Caveat: arch-unit-ts dot-path matchers may not handle parens cleanly. > The generated test includes a sanity check that catches silent > zero-match passes; a manual fallback using filterClasses() is provided > in the file. > - R3 — Private folders are implementation details [only show if _* > folders detected: list them] > Same parens-style caveat applies for leading underscores. > - R4 — Layered / hexagonal architecture [only show if domain/, > application/, or infrastructure/ detected] > Domain ⟂ application ⟂ infrastructure boundaries. > > Custom rules > Want to add or modify anything before I generate the file? You can: > - Enable any opt-in rule (R2/R3/R4) > - Add a custom rule (tell me which packages must not depend on which) > - Remove a default rule > - Just confirm and generate

Wait for the user to respond before proceeding. Apply their changes to the template plan.

Step 3: Confirm Strategy

Summarize the final decisions in a compact table and ask once more before writing files:

> Final architecture test setup > > | Setting | Value | > |---|---| > | Test file path | tests/architecture/architecture.test.ts | > | TypeScriptProject root | [. | src] | > | Rules enabled | [list of enabled rule IDs] | > | npm script | test:arch → vitest run tests/architecture | > | Pre-commit hook | dedicated block in .husky/pre-commit (separate from any > existing lint-staged setup) | > > Proceed?

Wait for confirmation.

Step 4: Install Dependencies

Install arch-unit-ts and (if missing) husky as dev dependencies. Use the detected package manager:

• npm install -D arch-unit-ts husky
• pnpm add -D arch-unit-ts husky
• yarn add -D arch-unit-ts husky
• bun add -d arch-unit-ts husky

Ask the user for confirmation before installing. Skip packages that are already installed.

After install, re-query context7 for the installed version of arch-unit-ts to confirm the import paths in the template are still valid.

Step 5: Scaffold the Architecture Spec

Read the template at ${CLAUDE_PLUGIN_ROOT}/skills/setup-arch-unit/templates/architecture.test.template.ts.

Write it to tests/architecture/architecture.test.ts, filling in the following placeholders based on Step 1 detection:

| Placeholder | Replacement | Example | |---|---|---| | {{SRC_ROOT}} | 'src' if src/ exists, otherwise '.' | 'src' | | {{SHARED_PACKAGES}} | Comma-separated '..foo..' strings for each detected shared folder | '..components..', '..lib..', '..hooks..' | | {{SHARED_SANITY_PREDICATE}} | JS expression on path that returns true for any shared package | path.includes('.components.') \|\| path.includes('.lib.') \|\| path.includes('.hooks.') |

For each opt-in rule the user enabled in Step 2, uncomment that block in the generated file and parameterize it (e.g. replace (GROUP_A)/(GROUP_B) with the actual route group names).

If the user added custom rules, append them as additional it(...) blocks inside the describe('Architecture', ...) and clearly label them with // Custom rule N — comments.

Step 6: Add the npm Script

Read package.json and add a test:arch script to the scripts object:

{
  "scripts": {
    "test:arch": "vitest run tests/architecture"
  }
}

If a test:arch script already exists with a different command, ask the user whether to overwrite or rename.

Do not modify any other scripts.

Step 7: Set Up the Pre-commit Hook

This step has two cases.

7a — No .husky/ directory

Initialize Husky:

• npm: npx husky init
• pnpm: pnpm dlx husky init
• yarn: yarn dlx husky init
• bun: bunx husky init

This creates .husky/pre-commit with a default npm test line. Replace its contents with only the arch-unit block from ${CLAUDE_PLUGIN_ROOT}/skills/setup-arch-unit/templates/precommit-block.sh.

7b — .husky/pre-commit exists

Read the file. Three sub-cases:

1. No nexa arch-unit block — append the contents of

templates/precommit-block.sh to the end of the file. Preserve everything already in the hook.

1. An existing nexa arch-unit block (detect via # >>> nexa arch-unit >>>

marker) — replace only the lines between the markers (inclusive) with the fresh block. This makes re-running the skill idempotent.

1. No Husky setup but .husky/pre-commit exists from another tool — ask

the user whether to proceed or abort.

Make the hook executable: chmod +x .husky/pre-commit.

Step 8: Run It Once to Verify (mandatory)

Execute npm run test:arch (or the equivalent for the detected package manager). Three outcomes:

1. All sanity checks pass and all rules pass — proceed to Step 9.
2. A sanity check fails with "should contain files, got 0" — the dot-path

matcher did not match a folder whose name contains parens or leading underscores. Tell the user and recommend the manual fallback at the bottom of the generated spec file (using filterClasses() + hasImport()). Offer to rewrite the failing rule using the fallback pattern.

1. A rule fails with an actual architectural violation — show the user the

violation. Ask whether to:

• Fix the violating code (out of scope for this skill — recommend

/implement or a manual edit)

• Mark the rule as a known follow-up (comment it out with a // TODO: and

a linked technical task)

• Reconsider whether the rule is correct

Do not declare the skill complete until the test command exits cleanly (either all pass, or the rules causing failures are explicitly deferred with TODOs).

Step 9: Update CLAUDE.md

Append the following section to the target project's CLAUDE.md (create the file if it doesn't exist).

If a ## Architecture Tests section already exists (check for ``), ask the user whether to overwrite or skip — do not silently duplicate.

~~~markdown

Architecture Tests

• Library: arch-unit-ts
• Spec file: tests/architecture/architecture.test.ts
• Run: npm run test:arch (also runs as a Vitest spec under the regular suite)
• Pre-commit: enforced via .husky/pre-commit (dedicated block, independent

of any lint-staged setup)

• Active rules: [list of enabled rule IDs and one-line descriptions]

Conventions

• New shared modules (under components/, lib/, hooks/, utils/, ui/)

must never import from app/ — only the other direction.

• When adding a new route group (app/(group)/), update the route-group

cross-import rule if R2 is enabled.

• When adding a layered module (domain/, application/, infrastructure/),

enable or extend R4 to reflect the new layer's allowed dependencies. ~~~

Do not remove or modify any other content in CLAUDE.md.

Step 10: Summary

Present a summary of what was created:

## Architecture Tests Configured

### Strategy
- Library: arch-unit-ts vX.Y.Z (installed)
- Test framework: Vitest
- Active rules: [list]
- Pre-commit: dedicated block in .husky/pre-commit

### Files Created/Updated
| File | Change |
|---|---|
| tests/architecture/architecture.test.ts | created (N rules enabled) |
| package.json | added `test:arch` script |
| .husky/pre-commit | [created / appended nexa arch-unit block] |
| CLAUDE.md | appended `## Architecture Tests` section |

### Verification
- `npm run test:arch`: [X passed, Y failed]
- Sanity checks: [all matched files / N folders matched 0 files — see fallback]

### Next Steps
- To enable a commented opt-in rule (route groups, private folders, layered
  architecture), uncomment it in tests/architecture/architecture.test.ts and
  re-run `npm run test:arch`.
- The hook runs on every commit. To bypass once (not recommended), use
  `git commit --no-verify`.
- If a sanity check ever flags a zero-match folder after a project rename,
  update the matcher patterns in the spec — folder structure changes can
  silently break package patterns.

Reference Templates

• Architecture spec: [templates/architecture.test.template.ts](templates/architecture.test.template.ts)
• Pre-commit block: [templates/precommit-block.sh](templates/precommit-block.sh)

Spec Template Placeholders

| Placeholder | Description | Example | |---|---|---| | {{SRC_ROOT}} | Root path passed to RelativePath.of() | 'src' or '.' | | {{SHARED_PACKAGES}} | Comma-separated dot-path patterns for shared folders | '..components..', '..lib..' | | {{SHARED_SANITY_PREDICATE}} | JS expression on a path string that returns true for any shared package | path.includes('.components.') \|\| path.includes('.lib.') |

Design Decisions

Why a separate hook block instead of integrating with setup-pre-commit

setup-pre-commit configures lint-staged for fast, staged-file-only checks (formatter, type-check on staged files, etc.). Arch-unit-ts is fundamentally a whole-project analysis — it must scan all files to resolve dependencies. Putting it inside lint-staged would either (a) feed it only staged files, breaking the analysis, or (b) run the full project scan on every staged-file invocation, which mixes concerns.

A dedicated labeled block in .husky/pre-commit keeps the two concerns independent: each skill manages only its own block, marked by # >>> nexa arch-unit >>> / # <<< nexa arch-unit <<<. Re-running this skill replaces only its block; re-running setup-pre-commit does not touch it.

Why the spec ships with a sanity check on every rule

arch-unit-ts package matchers like '..foo..' are silent when they match nothing — the rule passes vacuously and the user gains false confidence. Next.js folder names commonly contain parens (route groups) and leading underscores (private folders), both of which may interact unpredictably with the dot-path matcher. The sanity check (expect(matchedClasses.length).toBeGreaterThan(0)) turns a silent miss into a loud, named test failure on the very first run.

Why no CI workflow

Explicitly scoped out by the user. The pre-commit hook is the enforcement point. If the user later wants CI enforcement, npm run test:arch is already a standalone command and can be added to any CI job manually.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: nexadevapp
• Source: nexadevapp/nexa-claude-skills-marketplace
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.