Clean Code — Java/Spring Boot · Python · C · JS/TS · OOP

An Agent Skill that makes AI coding agents write senior-engineer quality code — SOLID, TDD, clean architecture, and language-specific practices — across Java/Spring Boot, Python, C, and JavaScript/TypeScript, with a shared OOP concepts foundation and cross-cutting SQL/API/concurrency guidance.

Installs into Claude Code, Cursor, Codex CLI, Antigravity, OpenCode, OpenClaw, and Hermes Agent with one command, and can be scoped to a single language so you're not carrying Python/C/JS reference docs around in a pure-Java project.

A full before/after comparison example (a real Spring Boot feature, built twice — with and without this skill) is included and detailed at the bottom of this README.

Table of Contents

• Why this exists
• What's inside
• Installation
  • Multi-agent support
  • Language-scoped install
  • All install options
• How the skill works
• Enforcement configs
• Repository structure
• Testing this repo
• Comparison Example: With Skill vs. Without Skill
• License

Why this exists

Agents left to their own defaults tend to produce code that runs but isn't maintainable: God classes, field injection, primitive obsession, entities leaking straight out of a REST API, no tests, silently swallowed exceptions. None of that shows up in a quick demo — it shows up six months later when the codebase needs to change.

This skill encodes the practices that prevent that, as reference documentation an agent loads and applies automatically, plus machine- enforceable lint/format configs so the guidance isn't just a suggestion the agent can forget three files later.

What's inside

| Principle | Focus | | ------------------ | ------------------------------------------------------------------------ | | TDD | Red-Green-Refactor, tests before code | | SOLID | All five principles, adapted per language (including C, which has no classes) | | OOP Fundamentals | Encapsulation, abstraction, inheritance, polymorphism — and their C equivalents (opaque pointers, function-pointer vtables) | | Clean Code | Naming, function size, formatting | | Design Patterns | GoF patterns, applied only when they remove real duplication | | Architecture | Layered/hexagonal boundaries, dependency rule | | SQL/Database | Schema design, indexing, N+1 detection, transactions, migrations | | API Design | REST resource modeling, status codes, idempotency, versioning | | Concurrency | Threading/async guidance across all four languages |

21 reference docs in total — see Repository structure.

Installation

Clone the repo and run it with npm, pnpm, or plain node — or install straight from npm.

git clone https://github.com/monishwar007/clean-code.git
cd clean-code
npm install            # or: pnpm install
node install.js --list # preview first, writes nothing

Note: the package is published on npm as @monishwar007/clean-code (scoped under the author's npm username). The CLI command itself stays clean-code either way.

npx @monishwar007/clean-code --list
pnpm dlx @monishwar007/clean-code --list

Once cloned, the same install can be triggered through package scripts too (useful if you want --agent/--lang flags to flow through a project's existing npm run/pnpm run workflow):

npm run install-skill -- --agent claude --lang java
pnpm run install-skill -- --agent claude --lang java

Multi-agent support

The skill folder (SKILL.md + references/) follows the open Agent Skills standard, so the same content works unmodified across every supported agent — they just look in different directories. install.js handles placing a copy in each:

| Agent(s) | Directory (project scope) | | ---------------------------------------- | --------------------------------- | | Claude Code | .claude/skills/senior-engineer/ | | Cursor | .cursor/skills/senior-engineer/ | | Codex CLI | .codex/skills/senior-engineer/ | | OpenClaw | .openclaw/skills/senior-engineer/ | | Antigravity, OpenCode, Hermes Agent | .agents/skills/senior-engineer/ (shared tool-agnostic location) |

node install.js --list      # preview first, writes nothing
node install.js             # install the full pack into every known agent

Install into specific agents only:

node install.js --agent claude,cursor

Agent Compatibility Note: Hermes Agent and some emerging tools don't have a publicly confirmed dedicated skills directory as of this writing. install.js places their copy at the tool-agnostic .agents/skills/ location (the same one Antigravity and OpenCode use), which is the safest current bet. If your version of one of these tools looks elsewhere, point it at that folder manually, or open an issue and the mapping in install.js's AGENT_INFO table can be updated.

Language-scoped install

Only writing Java? Don't install Python/C/JS reference docs you'll never load. --lang filters both the reference files copied and the SKILL.md router itself (its language-detection table, its Step 2 file list, and its non-negotiable-rules section are all trimmed to match):

node install.js --lang java

Installing "senior-engineer" (java) under /path/to/project:

  [ok] Claude Code -> .claude/skills/senior-engineer
  [ok] Cursor -> .cursor/skills/senior-engineer
  ...

19 files installed per agent.

Compare to a full install (23 files — the 4 extra are the 3 other language references plus their share of SKILL.md content). Combine with --agent freely:

node install.js --lang java --agent claude
node install.js --lang python,javascript --agent cursor,codex

All install options

node install.js [--agent <list>] [--lang <list>] [--target DIR] [--global] [--force] [--list]
npx @monishwar007/clean-code [same flags]
pnpm dlx @monishwar007/clean-code [same flags]

--agent   claude, cursor, codex, openclaw, antigravity, opencode, hermes, all (default: all)
--lang    java, python, c, javascript, all                                   (default: all)
--target  project root to install into                                       (default: cwd)
--global  install to each agent's home-directory (personal) location instead of --target
--force   overwrite an existing install
--list    preview only — prints what would be installed, writes nothing

Run npm test (or pnpm test) to validate the package structure and installer behavior — 23 automated checks covering every agent/language combination, reinstall protection, and marker-filtering correctness (see Testing this repo).

How the skill works

SKILL.md is the router an agent reads first. It:

1. Detects language context from file extensions / project markers (pom.xml → Java, requirements.txt → Python, Makefile → C, package.json → JS/TS), asking only when genuinely ambiguous.
2. Loads references by task type, not everything at once — writing new code loads a different, smaller set than reviewing a diff or designing architecture. See the task-loading table in SKILL.md.
3. Applies a TDD workflow: clarify → failing test → minimum code to pass → refactor against code-smells.md/solid-principles.md → check architecture boundaries → self-review against self-review-prompt.md before presenting the diff.
4. Defers to .claude/CLAUDE.md for scope discipline — this skill's design guidance operates inside "touch only what you must," not instead of it. SKILL.md has an explicit precedence section covering the cases that actually conflict (e.g. TDD is not "extra scope"; flagging an unrelated smell is not the same as fixing it unasked).

Enforcement configs

config/ ships machine-enforceable versions of the size/style guidance, so it's checked automatically instead of relying on the agent to remember it every time:

• .editorconfig — indentation/formatting, all languages
• checkstyle.xml — Java: method length, cyclomatic complexity, bans field injection, flags empty catch blocks
• ruff.toml — Python: complexity, required type annotations, bugbear checks
• .clang-format / .clang-tidy — C: formatting + defensive-programming static analysis (bugprone-, cert-)

Copy the relevant ones into a target project alongside the skill.

Repository structure

.claude/
└── CLAUDE.md                 # general behavioral guidelines (scope discipline, simplicity-first)
config/                       # machine-enforceable versions of the guidance
├── .editorconfig
├── checkstyle.xml
├── ruff.toml
├── .clang-format
└── .clang-tidy
skills/
└── senior-engineer/
    ├── SKILL.md               # router: language detection, task-based loading, workflow
    └── references/
        ├── solid-principles.md
        ├── oop-concepts.md
        ├── tdd.md
        ├── testing.md
        ├── clean-code.md
        ├── code-smells.md
        ├── design-patterns.md
        ├── architecture.md
        ├── object-design.md
        ├── complexity.md
        ├── limits.md            # canonical size/complexity numbers (single source of truth)
        ├── checklist.md         # terse pre-commit checklist
        ├── self-review-prompt.md
        ├── examples.md          # full before/after walkthroughs (Java, Python, C)
        ├── java-spring-boot.md
        ├── python.md
        ├── c-programming.md
        ├── javascript-typescript.md
        ├── sql-database.md
        ├── api-design.md
        └── concurrency.md
test/
├── structure.test.js         # validates package structure (files exist, no orphans)
└── install.test.js           # validates installer behavior across agents/languages
comparison-example/           # see "Comparison Example" section below
├── without-skill/
├── with-skill/
├── _stub-spring-api/
└── verify-compile.sh
install.js                    # multi-agent, language-filtered installer
package.json

Testing this repo

npm test

23 checks across two suites:

• structure.test.js — every reference file SKILL.md points to actually exists, every file in references/ is linked from somewhere, no orphaned/empty docs, all enforcement configs present, install.js is syntactically valid.
• install.test.js — default install writes exactly 5 physical directories (grouping shared-location agents correctly), --agent filters correctly, --lang java excludes the other three languages' reference files and leaves no leftover marker syntax in the generated SKILL.md, reinstall-without---force is blocked, --force succeeds, invalid --agent/--lang values fail with a clear message, --global resolves against $HOME.

Comparison Example: With Skill vs. Without Skill

To make the effect of this skill concrete rather than just asserted, the same feature — an Order Management REST endpoint (create an order with line items, apply a "10% off over ₹1000" discount, fetch an order, search by customer) — is implemented twice in comparison-example/:

• without-skill/ — how this typically gets written with no guidance.
• with-skill/ — the same feature with this skill's practices applied.

Both are real, complete Spring Boot Maven projects. Since this environment can't reach Maven Central, comparison-example/verify-compile.sh compiles both against a small hand-written stub of the Spring/JPA/JUnit/ Mockito API surface they actually use (_stub-spring-api/, 57 files) and actually runs the pure-JUnit test to confirm the discount math is genuinely correct, not just that the code parses:

$ cd comparison-example && ./verify-compile.sh
== Compiling without-skill/ ==
OK - 62 files compiled clean

== Compiling with-skill/ (main + test) ==
OK - 78 files compiled clean

== Running OrderPolicyTest for real (pure JUnit, no Mockito needed) ==
  PASS  com.example.orders.service.OrderPolicyTest#appliesTenPercentDiscountAboveThreshold
  PASS  com.example.orders.service.OrderPolicyTest#appliesNoDiscountAtOrBelowThreshold

Results: 2 passed, 0 failed

(OrderServiceTest/OrderControllerTest use Mockito, which the stub doesn't functionally implement — they're verified to compile/type-check correctly; a real mvn test would execute them against actual Mockito.)

Side-by-side

Without skill — one file, OrderController.java, does everything:

@RestController
@RequestMapping("/orders")
public class OrderController {

    @Autowired                              // field injection
    private OrderRepository orderRepository;

    @Autowired
    private EntityManager entityManager;

    @PostMapping
    public Order createOrder(@RequestBody Order order) {   // JPA entity as the API model
        double total = 0;                                   // double for money
        if (order.getItems() != null) {
            if (order.getItems().size() > 0) {
                for (OrderItem item : order.getItems()) {
                    if (item.getQuantity() > 0) {
                        total = total + (item.getPrice() * item.getQuantity());
                        item.setOrder(order);
                    }
                }
            }
        }
        if (total > 1000) {                                  // magic number, buried business rule
            total = total - (total * 0.1);
        }
        order.setTotal(total);
        order.setStatus("CREATED");                          // string, not an enum
        return orderRepository.save(order);                   // entity serialized straight back
    }

    @GetMapping("/search")
    public List<Order> search(@RequestParam String name) {
        String jpql = "SELECT o FROM Order o WHERE o.customerName = '" + name + "'"; // injection risk
        return entityManager.createQuery(jpql).getResultList();
    }

    @PutMapping("/{id}/status")
    public Map<String, String> updateStatus(@PathVariable Long id, @RequestParam String status) {
        Map<String, String> result = new HashMap<>();
        try {
            Order order = orderRepository.findById(id).orElse(null);
            order.setStatus(status);                           // NPE if id doesn't exist
            orderRepository.save(order);
            result.put("result", "ok");
        } catch (Exception e) {
            result.put("result", "error");                     // swallowed — caller gets no detail
        }
        return result;
    }
}

No service layer. No tests. No custom exceptions. Order/OrderItem are plain JPA entities with only getters/setters — an anemic model with all "logic" (such as it is) crammed into the controller.

With skill — the same feature, layered:

// domain/Order.java — entity owns its own invariants
public void addItem(OrderItem item) {
    items.add(item);
    item.assignTo(this);
}
public void applyDiscount(DiscountStrategy strategy) {   // tell, don't ask
    this.appliedDiscountRate = strategy.discountRateFor(subtotal());
}

// domain/ThresholdDiscountStrategy.java — Open/Closed: new rules are a
// new class, never an edit to tested code or a growing if-chain
public BigDecimal discountRateFor(Money subtotal) {
    return subtotal.isGreaterThan(threshold) ? rate : BigDecimal.ZERO;
}

// service/OrderService.java — constructor injection, transaction boundary
public OrderService(OrderRepository orderRepository, OrderPolicy orderPolicy) {
    this.orderRepository = orderRepository;
    this.orderPolicy = orderPolicy;
}
@Transactional
public Order createOrder(CreateOrderRequest request) { ... }

// repository/OrderRepository.java — parameterized, no string concatenation
@EntityGraph(attributePaths = "items")
List<Order> findByCustomerName(String customerName);

// controller/OrderController.java — pure delegation
@PostMapping
public ResponseEntity<OrderResponse> createOrder(@Valid @RequestBody CreateOrderRequest request) {
    Order order = orderService.createOrder(request);
    return ResponseEntity.status(201).body(OrderResponse.from(order));
}

Plus: a Money value object (BigDecimal-backed, no float rounding surprises), DTOs at the API boundary (Order the JPA entity never leaves the service layer), OrderNotFoundException + @RestControllerAdvice instead of a null-returning 200 or a swallowed exception, and three real test classes (OrderPolicyTest, OrderServiceTest, OrderControllerTest).

What changed, and which reference doc drove it

| Issue in without-skill/ | Fix in with-skill/ | Reference doc | | ------------------------------------------------------ | ------------------------------------------------------ | ------------------------------ | | Field injection (@Autowired on a field) | Constructor injection | java-spring-boot.md | | JPA entity returned directly from the API | DTOs (CreateOrderRequest/OrderResponse) at the boundary | architecture.md, api-design.md | | double for money | Money value object over BigDecimal | object-design.md, java-spring-boot.md | | Discount rule as a hardcoded if + magic number | DiscountStrategy interface + ThresholdDiscountStrategy | design-patterns.md (Strategy, OCP) | | String-concatenated JPQL (injection risk) | Spring Data derived query, parameterized automatically | sql-database.md | | Missing order → NPE / silent null 200 response | OrderNotFoundException + @RestControllerAdvice | code-smells.md, java-spring-boot.md | | Swallowed exception in updateStatus | No equivalent path left unhandled; errors surface with detail | clean-code.md (error handling) | | Everything in one OrderController God class | Controller → Service → Domain → Repository layering | architecture.md | | Zero tests | OrderPolicyTest, OrderServiceTest, OrderControllerTest (TDD-first) | tdd.md, testing.md |

Reproduce it yourself

cd comparison-example
./verify-compile.sh          # compile-check + run OrderPolicyTest for real
cd with-skill && mvn test    # full test suite with real Mockito/JUnit (needs Maven Central access)

License

MIT