Make Claude Code Follow DRY Principle (2026)

Three different files contain the same email validation regex. Two services implement identical retry logic. A formatting function exists in four variations across the codebase. Claude Code creates new implementations instead of reusing existing ones.

The Problem

DRY (Don’t Repeat Yourself) violations from Claude Code:

  • Duplicated validation logic across files
  • Copy-pasted error handling patterns
  • Multiple implementations of the same algorithm
  • Repeated configuration objects
  • Identical type definitions in different modules

Root Cause

Claude Code processes one request at a time. When you ask it to add validation to a form, it writes validation code — without checking if identical validation exists elsewhere. The model does not perform a codebase-wide deduplication scan before generating code.

The Fix

The SuperClaude Framework enforces DRY through its /sc:implement command, which checks existing code before creating new code. Combine this with a utility registry in CLAUDE.md.

Step 1: Create a Shared Code Registry

## Shared Code — USE THESE, DO NOT RECREATE
### Validation (src/utils/validation.ts)
- validateEmail, validatePhone, validateUrl
- validateRequired, validateMinLength, validateMaxLength
- validateRange, validatePattern, validateEnum
### Error Handling (src/utils/errors.ts)
- AppError class (code, message, statusCode)
- withErrorHandling(fn) — wraps async functions with try/catch
- retryWithBackoff(fn, maxRetries) — retry with exponential backoff
### Formatting (src/utils/format.ts)
- formatCurrency, formatDate, formatPhoneNumber
- formatFileSize, formatDuration, formatPercentage
### HTTP (src/lib/api.ts)
- apiClient — pre-configured ky instance with auth, retry, error handling
- DO NOT create new HTTP client instances

Step 2: Add the DRY Check Rule

## DRY Protocol — MANDATORY
Before writing ANY utility function:
1. Search src/utils/ and src/lib/ for existing implementations
2. If a function does 70%+ of what you need, extend it
3. If extending is not feasible, create a new function in the SAME file as related functions
4. NEVER create a standalone utility file for a single function
Before writing ANY logic that might already exist:
1. grep for key terms (e.g., "retry", "validate", "format")
2. Check existing test files for usage patterns
3. If you find duplicate logic, refactor into shared utility FIRST

Step 3: Enforce Centralized Patterns

## Pattern Centralization
These patterns are implemented ONCE and imported everywhere:
### Retry pattern: src/utils/errors.ts → retryWithBackoff()
### Auth check: src/middleware/auth.ts → requireAuth()
### Pagination: src/utils/pagination.ts → paginate()
### Cache wrapper: src/lib/cache.ts → withCache()
### Rate limiting: src/middleware/rate-limit.ts → rateLimit()
If you need one of these patterns, import from the central location.
Do not implement your own version.

CLAUDE.md Code to Add

## Deduplication Check
After writing any code:
1. Count how many times the same logic pattern appears in the codebase
2. If the pattern appears 3+ times, extract it into a shared utility
3. If you are about to write logic that is similar to existing code, stop and refactor

Verification

  1. Ask Claude Code to add input validation to a new form
  2. Check: Does it import from src/utils/validation.ts?
  3. Ask: “Is there any duplicated logic in this codebase?”
  4. Claude Code should identify and propose consolidation

Prevention

Add code duplication detection to your CI:

npx jscpd src/ --threshold 3 --reporters console

This flags any block of code that appears 3+ times. The awesome-claude-code-toolkit includes deduplication plugins for ongoing monitoring.

For more on code reuse, see the duplicate code fix guide. For utility organization patterns, read the CLAUDE.md best practices guide. For team standards that prevent duplication, check the team onboarding playbook.

Frequently Asked Questions

Does this error affect all operating systems?

This error can occur on macOS, Linux, and Windows (WSL). The exact error message may differ slightly between platforms, but the root cause and fix are the same. macOS users may see additional Gatekeeper or notarization prompts. Linux users should check that the relevant system packages are installed. Windows users should ensure they are running inside WSL2, not native Windows.

Will this error come back after updating Claude Code?

Updates can occasionally reintroduce this error if the update changes default configurations or dependency requirements. After updating Claude Code, verify your project still builds and runs correctly. If the error returns, reapply the fix and check the changelog for breaking changes.

Can this error cause data loss?

No, this error occurs before or during an operation and does not corrupt existing files. Claude Code’s edit operations are atomic — they either complete fully or not at all. However, if the error occurs during a multi-step operation, you may have partial changes that need to be reviewed with git diff before continuing.

How do I report this error to Anthropic if the fix does not work?

Open an issue at github.com/anthropics/claude-code with: (1) the full error message including stack trace, (2) your Node.js version (node --version), (3) your Claude Code version (claude --version), (4) your operating system and version, and (5) the command or operation that triggered the error.

This fix also applies if you see variations of this error:

  • Connection or process errors with similar root causes in the same subsystem
  • Timeout variants where the operation starts but does not complete
  • Permission variants where access is denied to the same resource
  • Configuration variants where the same setting is missing or malformed

If your specific error message differs slightly from the one shown above, the fix is likely the same. The key indicator is the operation that failed (shown in the stack trace) rather than the exact wording of the message.

Try it: Paste your error into our Error Diagnostic for an instant fix.