Coding Standards

Universal Coding Standards

Technical Anti-patterns (Red Flag Patterns)

When any pattern below is detected, pause implementation and record: the triggered pattern, affected current requirement, smallest compliant alternative, and verification needed to resume. Resume when the alternative removes the pattern or a documented requirement justifies retaining it.

Code Quality Anti-patterns

1. Writing similar code 3 or more times - Violates Rule of Three
2. Multiple responsibilities mixed in a single file - Violates Single Responsibility Principle (SRP)
3. Defining same content in multiple files - Violates DRY principle
4. Making changes without checking dependencies - Potential for unexpected impacts
5. Disabling code with comments - Should use version control
6. Error suppression - Hiding problems creates technical debt
7. Type assertions standing in for a guarantee - Declaring a type that neither a runtime check nor an existing contract establishes

Design Anti-patterns

• "Make it work for now" thinking - Accumulation of technical debt
• Patchwork implementation - Unplanned additions to existing code
• Optimistic implementation of uncertain technology - Designing unknown elements assuming "it'll probably work"
• Symptomatic fixes - Surface-level fixes that don't solve root causes
• Unplanned large-scale changes - Lack of incremental approach

Basic Principles

Inspect until the evidence identifies the lowest-total-complexity solution that delivers the required user, operator, or maintainer value while keeping the system correct and maintainable.

• Evidence-Bounded Refactoring - Refactor code that blocks the current outcome, is changed by the current task, or fails an applicable quality check; use small behavior-preserving steps. Report other findings with their owning boundary and evidence without expanding the active change
• Current-Requirement Code Only - Introduce code paths, capabilities, infrastructure, abstractions, or speculative edge-case handling when a current requirement, verified constraint, or evidence-backed material risk requires them (YAGNI)
• Design Convergence - Deliver the current required outcome with the least new design surface. Before introducing persistent state, a public or cross-boundary contract, a behavioral mode, a reusable abstraction, or a component split, record what the existing capabilities already deliver, what they fail to deliver for the current outcome, and why the addition is the smallest thing that closes that gap

Judge total complexity across every activated surface: user decisions, settings, modes, concepts, outputs, persistent state, and implementation paths, together with their UX, runtime, implementation, testing, documentation, and maintenance cost. Compare only dimensions that differ between viable approaches. Prefer reuse or no new mechanism when it delivers the same confirmed value and proof at lower total complexity.

Comment Writing Rules

• Code first: Names, types, and structure are the primary medium; add a comment only when it carries what the code cannot express. When in doubt, improve the name instead of commenting
• Comment the "why", not the "what": Explain reasoning, trade-offs, constraints/edge cases, or public API contracts
• Timeless Content: Comments contain current reasoning, constraints, edge cases, or API contracts; version control retains development history
• Timeless: Write only content that remains valid whenever read
• Conciseness: Keep explanations to necessary minimum

Error Handling Fundamentals

Fail-Fast Principle

Fail quickly on errors to prevent processing continuation in invalid states. Propagate the failure or return an explicit typed error with the original diagnostic context.

For detailed implementation methods (Result type, custom error classes, layered error handling, etc.), refer to language and framework-specific rules.

Rule of Three - Criteria for Code Duplication

How to handle duplicate code based on Martin Fowler's "Refactoring":

Criteria for Commonalization

Cases for Commonalization

• Business logic duplication
• Complex processing algorithms
• Areas likely requiring bulk changes
• Validation rules

Cases to Keep Separate

• Accidental matches (coincidentally same code)
• Possibility of evolving in different directions
• Significant readability decrease from commonalization
• Simple helpers in test code

Change Boundary and Reference Representativeness

Prompt paths are investigation starting points. Include another repository file when evidence shows that it implements the accepted outcome, is a required dependency or wiring path, or must change to preserve a contract affected by the work. Callers, consumers, tests, configuration, imports, and data flow are useful evidence rather than a required checklist.

When adopting a pattern, API, or dependency, inspect the relevant feature and repository uses that share its responsibility and current contract. Prefer the compatible implementation in that responsibility. Frequency helps locate candidates but does not make a pattern authoritative; when approaches coexist, use their callers, lifecycle, and compatibility to distinguish the current pattern from a legacy or unrelated one.

Resolve external dependency versions from manifests, lockfiles, and compatible consumers. Escalate only when those sources cannot resolve a choice that changes compatibility or architecture.

Common Failure Patterns and Avoidance Methods

Pattern 1: Error Fix Chain

Symptom: Fixing one error causes new errors Cause: Surface-level fixes without understanding root cause Avoidance: Identify root cause with 5 Whys before fixing

Pattern 2: Circumventing Type Guarantees

Symptom: any or as declares a type that no check or contract establishes Cause: Impulse to avoid type errors Avoidance: Apply the evidence criteria in Type Safety Fundamentals.

Pattern 3: Implementation Without Sufficient Testing

Symptom: Many bugs after implementation Cause: Ignoring Red-Green-Refactor process Avoidance: Start behavior changes with a failing test that demonstrates the required outcome

Pattern 4: Ignoring Technical Uncertainty

Symptom: Frequent unexpected errors when introducing new technology Cause: Assuming "it should work according to official documentation" without prior investigation Avoidance:

• Record certainty evaluation at the beginning of task files
• Treat certainty as low when repository evidence, a version-matched primary source, or a runnable local check cannot confirm an outcome-relevant behavior; create the smallest verification that resolves that behavior before implementation

Pattern 5: Insufficient Existing Code Investigation

Symptom: Duplicate implementations, architecture inconsistency, integration failures, adopting outdated patterns Cause: Insufficient understanding of existing code before implementation; referencing only nearby files without verifying representativeness Avoidance Methods:

• Before implementation, search for similar functionality using domain, responsibility, and configuration-pattern keywords
• Similar functionality found -> Use or extend that implementation when it satisfies the current contract
• Similar functionality is technical debt -> Repair it when it blocks the current outcome, was caused by the current change, or lies in confirmed scope; otherwise report it separately. Create an ADR when the repair requires an architectural decision
• No similar functionality exists -> Implement new functionality following existing design philosophy
• Record every decision and its rationale in the artifact the current workflow assigns to it
• Reference representativeness check: See the "Change Boundary and Reference Representativeness" section above

Debugging Techniques

5 Whys - Root Cause Analysis

Trace each answer to observed evidence until reaching a cause whose correction prevents the original failure. Record each question, evidence, and the final causal link; stop when the next answer would be speculation and name the evidence needed.