Implement Simplicity First in CLAUDE.md (2026)

Production-ready CLAUDE.md blocks that stop Claude Code from overengineering. Each version includes a complexity budget, abstraction gates, and concrete rules for file creation.

The Principle

Start with the simplest solution that works. Add complexity only when requirements force it. See the principle overview for background.

Why It Matters

Overengineering is Claude Code’s most expensive default behavior. A 50-line solution ballooned to 300 lines across 6 files costs 6x more tokens to generate, takes longer to review, and introduces maintenance burden for abstractions you didn’t ask for.

CLAUDE.md Implementation

Minimal Version

## Simplicity Rule
- Implement the simplest version that works. No preemptive abstractions.
- If a function works, don't wrap it in a class.
- If inline code works, don't extract it to a utility.
- Ask: "Would the simplest approach work here?" If yes, use it.

Standard Version

## Simplicity First — Complexity Budget
### File Budget
- A task that could be done in 1 file should not create 3 files.
- Before creating a new file, explain why existing files can't hold this code.
### Abstraction Gate
- Interfaces/abstract classes: only when 3+ concrete implementations exist NOW (not "might exist later")
- Factory/builder patterns: only when construction logic is genuinely complex (5+ parameters, conditional assembly)
- Event systems: only when 3+ independent consumers need the same event
- Plugin/middleware patterns: only when the extension point is an explicit requirement
### Indirection Limit
- Maximum 1 hop between the caller and the actual work. If A calls B which calls C which does the work, flatten to A calls C.
- Exception: framework-required layers (middleware in Express, route handlers in Next.js)
### Code Budget
- If the simple version is under 50 lines, do not create an abstracted version.
- If the simple version is 50-200 lines, add abstraction only if there's clear repetition.
- Over 200 lines: discuss decomposition approach before implementing.

Strict Version

## Simplicity First — Strict Mode
### BEFORE writing ANY code, answer:
1. What is the minimum code needed to satisfy this requirement?
2. Am I adding anything "just in case" or "for future flexibility"?
3. Would a junior developer understand this in under 5 minutes?
### NEVER (without explicit request):
- Create abstract base classes with single implementations
- Add dependency injection containers
- Build configuration systems for fewer than 5 config values
- Create utility files for functions used in only one place
- Implement observer/event patterns for fewer than 3 consumers
- Add caching layers without measured performance problems
- Create type-safe builders for simple object construction
### ALWAYS prefer:
- Functions over classes (for stateless operations)
- Direct imports over dependency injection (unless testing demands it)
- Hardcoded values over config files (for 1-3 values)
- Inline validation over validation frameworks (for 1-3 fields)
- String concatenation over template engines (for simple strings)
- If/else over strategy pattern (for 2-3 branches)

Before/After Examples

Before: Over-Abstracted Logger

// Claude Code without simplicity rules
interface LogTransport { write(msg: string): void; }
class ConsoleTransport implements LogTransport { /* ... */ }
class FileTransport implements LogTransport { /* ... */ }
class Logger {
  private transports: LogTransport[] = [];
  addTransport(t: LogTransport) { this.transports.push(t); }
  log(level: string, msg: string) {
    this.transports.forEach(t => t.write(`[${level}] ${msg}`));
  }
}
// + factory + config + 3 files + 80 lines

After: Simple Logger

// With simplicity rules — project only needs console logging
function log(level: 'info' | 'warn' | 'error', msg: string) {
  console.log(`[${level}] ${new Date().toISOString()} ${msg}`);
}

5 lines. If the project later needs file transport, refactor then.

Before: Config System for 3 Values

// Claude Code builds a config system
const config = new ConfigLoader()
  .fromEnv()
  .fromFile('.config.json')
  .withDefaults({ port: 3000, host: 'localhost', debug: false })
  .validate(ConfigSchema)
  .build();
// + 3 files + 120 lines

After: Direct Values

const PORT = parseInt(process.env.PORT ?? '3000');
const HOST = process.env.HOST ?? 'localhost';
const DEBUG = process.env.DEBUG === 'true';

3 lines. No config loader, no schema, no file parsing.

Common Mistakes

  1. Banning all patterns — the goal isn’t zero abstractions. It’s zero premature abstractions. When complexity is earned (3+ implementations, measured performance problems, explicit extensibility requirements), use patterns.

  2. Strict mode in creative exploration — if you’re prototyping and don’t know what you’re building yet, strict simplicity can be too constraining. Use the minimal version during exploration.

  3. Not accounting for team size — solo developers can hold more context, so simpler code works well. Large teams may need more structure for coordination. Calibrate accordingly.

Frequently Asked Questions

Do I need a paid Anthropic plan to use this?

Claude Code works with any Anthropic API plan, including the free tier. However, the free tier has lower rate limits (requests per minute and tokens per minute) that may slow down multi-step workflows. For professional use, the Build or Scale plan provides higher limits and priority access during peak hours.

How does this affect token usage and cost?

The token cost depends on the size of your prompts and Claude’s responses. Typical development tasks consume 10K-50K tokens per interaction. Using a CLAUDE.md file and skills reduces exploration tokens by 50-80%, which directly lowers costs. Monitor your usage at console.anthropic.com/settings/billing.

Can I customize this for my specific project?

Yes. All Claude Code behavior can be customized through CLAUDE.md (project rules), .claude/settings.json (permissions), and .claude/skills/ (domain knowledge). The most impactful customization is adding your project’s specific patterns, conventions, and common commands to CLAUDE.md so Claude Code follows your standards from the start.

What happens when Claude Code makes a mistake?

Claude Code creates files and edits through standard filesystem operations, so all changes are visible in git diff. If a change is wrong, revert it with git checkout -- <file> for a single file or git stash for all changes. Claude Code does not make irreversible changes unless you explicitly allow destructive commands in settings.json.

Practical Details

When working with Claude Code on this topic, keep these implementation details in mind:

Project Configuration. Your CLAUDE.md should include specific references to how your project handles this area. Include file paths, naming conventions, and any project-specific patterns that differ from defaults. Claude Code reads this file at session start and uses it to guide all operations.

Integration with Existing Tools. Claude Code works alongside your existing development tools rather than replacing them. It respects .gitignore for file visibility, uses your project’s installed dependencies, and follows the build/test scripts defined in package.json (or equivalent). Ensure your toolchain is working correctly before involving Claude Code.

Performance Considerations. For large codebases (10,000+ files), Claude Code’s file scanning can be slow if not properly scoped. Use .claudeignore to exclude generated directories (dist, build, .next, coverage) and dependency directories (node_modules, vendor). This typically reduces scan time by 80-90%.

Version Control Integration. All changes Claude Code makes are regular filesystem operations visible to git. Use git diff after each significant change to review what was modified. For experimental changes, create a branch first with git checkout -b experiment/topic so you can easily discard or keep the results.

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