Clean Code Standard

This skill is the authoritative clean code standard for this repository's shared skills. It defines stable rule IDs (CC-*), how to apply them in reviews, and how to extend them safely via language overlays and explicit exceptions.

Judgment over dogma: This standard's CC-* rules are durable (coupling/cohesion, naming, small interfaces, explicit errors). Numeric folklore — hard function-length caps, "comments are a smell," DRY applied absolutely — is not. Robert C. Martin's Clean Code (2nd ed., 2025) and John Ousterhout's A Philosophy of Software Design disagree in a published, public debate on function size and commenting (see references/code-quality-operational-playbook.md § 14); apply the rule ID's intent, not a book's specific numeric prescription, and know when not to refactor (§ 14.3 of the same reference).

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Quick Reference

Task	Tool/Framework	Command	When to Use
Cite a standard	CC-* rule ID	N/A	PR review comments, design discussions, postmortems
Categorize feedback	CC-NAM, CC-ERR, CC-SEC, etc.	N/A	Keep feedback consistent without "style wars"
Add stack nuance	Language overlay	N/A	When the base rule is too generic for a language/framework
Allow an exception	Waiver record	N/A	When a rule must be violated with explicit risk
Reuse shared checklists	assets/checklists/	N/A	When you need product-agnostic review/release checklists
Reuse utility patterns	references/*-utilities.md	N/A	When extracting shared auth/logging/errors/resilience/testing utilities

When to Use This Skill

• Defining or enforcing clean code rules across teams and languages.
• Mapping a concrete review or scanner finding to a CC-* ID; use software-code-review for the review workflow.
• Building automation: map linters/CI gates to CC-* IDs.
• Resolving recurring review debates: align on rule IDs, scope, and exceptions.

When NOT to Use This Skill

• Deep security audits → software-security-appsec for OWASP/SAST deep dives beyond CC-SEC-* baseline.
• Review workflow mechanics → software-code-review for PR workflow, reviewer assignment, and feedback patterns.
• Refactoring execution → qa-refactoring for step-by-step refactoring patterns and quality gates.
• Architecture decisions → software-architecture-design for system-level tradeoffs beyond code-level rules.

Workflow

1. Decide whether the request is about a base rule, an overlay, or an exception.
2. Route security, review-process, or refactoring mechanics to the adjacent skill if that is the real problem.
3. Anchor the guidance in existing CC-* rules before proposing new wording or automation; map a tool finding by its failure mode, not by tool severity alone.
4. Apply the relevant standard, overlay, or waiver pattern with explicit scope and rationale.
5. Cross-check against the navigation references before adding or revising durable standards.

Rule Application Checklist

When citing or enforcing CC-* rules in a review:

• Rule ID cited explicitly (not paraphrased) — e.g. CC-SEC-01, CC-ERR-03 (two-digit CC-<CAT>-<NN>; only IDs that exist in the catalog — python3 scripts/check_cc_ids.py [paths] fails on unknown IDs)
• Scope stated: file, module, service, or whole repo
• Language overlay applied if the repo is language-specific and the base rule is ambiguous
• Blocking vs advisory: correctness/security findings block merge; style findings are advisory
• Waiver path documented if the rule genuinely cannot be satisfied without architectural change

Decision Tree: Base Rule vs Overlay vs Exception

Feedback needed: [What kind of guidance is this?]
    ├─ Universal, cross-language rule? → Add/modify `CC-*` in `references/clean-code-standard.md`
    │
    ├─ Language/framework-specific nuance? → Add overlay entry referencing existing `CC-*`
    │
    └─ One-off constraint or temporary tradeoff?
        ├─ Timeboxed? → Add waiver with expiry + tracking issue
        └─ Permanent? → Propose a new rule or revise scope/exception criteria

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Optional: AI/Automation

Refactor evidence gate.

Do not raise a rule violation solely because code looks unfashionable. Name the maintenance failure it causes: duplicated change, hidden side effect, unsafe coupling, unreadable control flow, or measured complexity hotspot. Preserve stable awkward code when the proposed rewrite lacks a behavior-preserving test or a concrete reduction in change risk; document a narrow exception instead of creating churn.

• Map automation findings through the rule-level examples; inspect the code before assigning a priority.
• Keep AI-assisted suggestions advisory; human reviewers approve/deny with rule citations (https://conventionalcomments.org/).
• Gate new blocking violations against the repository baseline; track erosion and verbosity as reviewed trajectories rather than universal thresholds (metric guidance).

Reviewing AI-Generated Code

AI-generated code requires the same CC-* standards plus additional vigilance for these patterns:

Pattern	CC-* Mapping	Detection
Hallucinated imports	CC-SEC-05	npm info / pip index / type-check fails
Stale or deprecated APIs	CC-DEP-01	Compiler warnings, changelog checks
Missing error paths	CC-ERR-01, CC-ERR-04	No catch/finally, no null guards, no timeout
Premature abstraction	CC-FUN-06	Wrappers with single call site, unused generics
Confident wrong comments	CC-DOC-01, CC-DOC-02	Docstrings that don't match implementation
Security anti-patterns	CC-SEC-08, CC-SEC-03	String concatenation in queries, hardcoded tokens
Silent fallback or empty catch	CC-ERR-01	Error path returns a plausible default with no caller-visible failure
Weakened or deleted assertion	CC-TST-01, CC-TST-03	Requirement no longer makes a test fail when reversed
Duplicate helper or scope expansion	CC-FUN-05, CC-FUN-06	Parallel helper appears beside existing behavior or an abstraction has no second use

For agent change discipline and tests that detect regressions, use coding-behavior.md. For detailed hallucination checks, see references/code-quality-operational-playbook.md § 11.3.

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Navigation

Resources

• references/clean-code-standard.md — the CC-* rule definitions themselves; open first to find or cite a rule ID
• references/code-quality-operational-playbook.md — Operational playbook: LLM-code review, complexity management, peer-review controls, judgment over dogma (legacy RULE-01–13 retired; § 1 maps them to CC-*)
• references/working-effectively-with-legacy-code-operational-checklist.md — safely changing code with no/weak tests (Feathers)
• references/refactoring-operational-checklist.md — behavior-preserving refactor recipes and preconditions (Fowler)
• references/design-patterns-operational-checklist.md — when a GoF pattern earns its complexity vs. over-engineering
• references/functional-programming-patterns.md — Result/Either types, pipe/compose, immutability, pure functions, railway-oriented programming, CC-* rule mapping
• references/code-complexity-metrics.md — Cyclomatic/cognitive complexity, Halstead metrics, nesting depth, tooling (ESLint, Biome, Oxlint, SonarQube, Ruff), refactoring triggers
• data/sources.json — Current external references for review, security-by-design, observability, and modern tooling (official docs first)

Templates

• assets/checklists/backend-api-review-checklist.md
• assets/checklists/secure-code-review-checklist.md
• assets/checklists/frontend-performance-a11y-checklist.md
• assets/checklists/mobile-release-checklist.md
• assets/checklists/ux-design-review-checklist.md

Utility Patterns

• references/utility-patterns.md — When and how to extract a utility instead of duplicating code (the decision guide above the concrete utilities below)
• references/auth-utilities.md
• references/error-handling.md
• references/config-validation.md
• references/resilience-utilities.md
• references/logging-utilities.md
• references/observability-utilities.md
• references/testing-utilities.md
• references/llm-utilities.md

Related Skills

• ../software-code-review/SKILL.md — Review workflow and judgment; cite CC-* IDs
• ../software-security-appsec/SKILL.md — Security deep dives beyond baseline CC-SEC-*
• ../qa-refactoring/SKILL.md — Refactoring execution patterns and quality gates
• ../software-architecture-design/SKILL.md — System-level tradeoffs and boundaries

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Freshness Protocol

• For a named linter or scanner, check its official rule documentation and the version resolved by the project before mapping a finding to CC-*.
• For a proposed CI gate, check the scanner's current baseline/new-code support and compare its rule coverage with the repository's existing checks.
• Report the selected rule mapping, any unsupported rule or migration risk, and the source used to verify it.

Known Traps

• Treating “clean code” as style preference only and ignoring correctness, observability, security, and change safety.
• Enforcing blanket abstraction rules that increase indirection and reduce runtime clarity in the name of cleanliness.
• Mixing language-specific formatter and linter opinions into universal guidance without preserving the stable CC rule intent.
• Letting tool defaults silently redefine the team standard when the explicit repository rule IDs say otherwise.
• Auditing code solely from static style output and missing failure-mode, data-boundary, and operability risks.

Common Anti-Patterns

• Replacing concrete, understandable code with layered abstractions just to satisfy a cleanliness aesthetic.
• Treating short functions, DRY, or naming rules as absolute even when they harm cohesion, locality, or domain clarity.
• Using “clean code” to block pragmatic duplication that preserves boundaries or avoids premature frameworks.
• Turning rule IDs into checklist theater with no explanation of why the rule matters for maintainability or safety.
• Applying one language ecosystem’s conventions wholesale to another without adaptation for tooling, runtime, and team workflow.

Learnings Loop

When prior decisions or pitfalls are relevant, consult learnings.consolidated.md if present; use learnings.md only for needed history or as the available fallback. Otherwise skip both.

After applying it, if you encountered a pattern worth remembering, a mistake worth preventing, or a domain fact that surprised you, append one dated bullet to learnings.md via agents-skills-feedback-loop/scripts/append_learning.py. Do not modify SKILL.md itself.