Code Deduplication

by alinaqi72a456e6ccf0No license707 starsListed Oct 8, 2026Updated Oct 8, 2026Repository updated 2 weeks ago

Prevent semantic code duplication with capability index and check-before-write

AI-generated overview

Prevents semantic code duplication by maintaining a capability index and checking for existing functions before writing new code.

What it does: This skill defines a workflow for avoiding duplicate code by keeping a CODE_INDEX.md file that catalogs existing functions, hooks, and components by capability rather than file location. It specifies check-before-write steps, file header and function documentation formats, and a periodic audit checklist for finding overlapping implementations. It also describes optional vector database indexing for large codebases.
When to use it: Use it before creating new utility functions or shared code, or when adding functionality that may already exist in the codebase. It is also intended for periodic audits of semantic overlap across utilities, API calls, validation, error handling, components, and hooks.
Requirements: No scripts are shipped; it is instructions only. It expects a project codebase and, for the optional vector search setup, Python with ChromaDB or LanceDB.

Code Deduplication Skill

Purpose: Prevent semantic duplication and code bloat. Maintain a capability index so Claude always knows what exists before writing something new.

Core Philosophy

┌─────────────────────────────────────────────────────────────────┐│  CHECK BEFORE YOU WRITE                                         ││  ─────────────────────────────────────────────────────────────  ││  AI doesn't copy/paste - it reimplements.                       ││  The problem isn't duplicate code, it's duplicate PURPOSE.      ││                                                                 ││  Before writing ANY new function:                               ││  1. Check CODE_INDEX.md for existing capabilities               ││  2. Search codebase for similar functionality                   ││  3. Extend existing code if possible                            ││  4. Only create new if nothing suitable exists                  │├─────────────────────────────────────────────────────────────────┤│  AFTER WRITING: Update the index immediately.                   ││  PERIODICALLY: Run /audit-duplicates to catch overlap.          │└─────────────────────────────────────────────────────────────────┘

┌─────────────────────────────────────────────────────────────────┐│  CHECK BEFORE YOU WRITE                                         ││  ─────────────────────────────────────────────────────────────  ││  AI doesn't copy/paste - it reimplements.                       ││  The problem isn't duplicate code, it's duplicate PURPOSE.      ││                                                                 ││  Before writing ANY new function:                               ││  1. Check CODE_INDEX.md for existing capabilities               ││  2. Search codebase for similar functionality                   ││  3. Extend existing code if possible                            ││  4. Only create new if nothing suitable exists                  │├─────────────────────────────────────────────────────────────────┤│  AFTER WRITING: Update the index immediately.                   ││  PERIODICALLY: Run /audit-duplicates to catch overlap.          │└─────────────────────────────────────────────────────────────────┘

Code Index Structure

Maintain CODE_INDEX.md in project root, organized by capability not file location:

markdown

# Code Index
*Last updated: [timestamp]**Run `/update-code-index` to regenerate*
## Quick Reference
| Category | Count | Location ||----------|-------|----------|| Date/Time | 5 functions | src/utils/dates.ts || Validation | 8 functions | src/utils/validate.ts || API Clients | 12 functions | src/api/*.ts || Auth | 6 functions | src/auth/*.ts |
---
## Date/Time Operations
| Function | Location | Does What | Params ||----------|----------|-----------|--------|| `formatDate()` | utils/dates.ts:15 | Formats Date → "Jan 15, 2024" | `(date: Date, format?: string)` || `formatRelative()` | utils/dates.ts:32 | Formats Date → "2 days ago" | `(date: Date)` || `parseDate()` | utils/dates.ts:48 | Parses string → Date | `(str: string, format?: string)` || `isExpired()` | auth/tokens.ts:22 | Checks if timestamp past now | `(timestamp: number)` || `addDays()` | utils/dates.ts:61 | Adds days to date | `(date: Date, days: number)` |
---
## Validation
| Function | Location | Does What | Params ||----------|----------|-----------|--------|| `isEmail()` | utils/validate.ts:10 | Validates email format | `(email: string)` || `isPhone()` | utils/validate.ts:25 | Validates phone with country | `(phone: string, country?: string)` || `isURL()` | utils/validate.ts:42 | Validates URL format | `(url: string)` || `isUUID()` | utils/validate.ts:55 | Validates UUID v4 | `(id: string)` || `sanitizeHTML()` | utils/sanitize.ts:12 | Strips XSS from input | `(html: string)` || `sanitizeSQL()` | utils/sanitize.ts:28 | Escapes SQL special chars | `(input: string)` |
---
## String Operations
| Function | Location | Does What | Params ||----------|----------|-----------|--------|| `slugify()` | utils/strings.ts:8 | Converts to URL slug | `(str: string)` || `truncate()` | utils/strings.ts:20 | Truncates with ellipsis | `(str: string, len: number)` || `capitalize()` | utils/strings.ts:32 | Capitalizes first letter | `(str: string)` || `pluralize()` | utils/strings.ts:40 | Adds s/es correctly | `(word: string, count: number)` |
---
## API Clients
| Function | Location | Does What | Returns ||----------|----------|-----------|---------|| `fetchUser()` | api/users.ts:15 | GET /users/:id | `Promise<User>` || `fetchUsers()` | api/users.ts:28 | GET /users with pagination | `Promise<User[]>` || `createUser()` | api/users.ts:45 | POST /users | `Promise<User>` || `updateUser()` | api/users.ts:62 | PATCH /users/:id | `Promise<User>` || `deleteUser()` | api/users.ts:78 | DELETE /users/:id | `Promise<void>` |
---
## Error Handling
| Function/Class | Location | Does What ||----------------|----------|-----------|| `AppError` | utils/errors.ts:5 | Base error class with code || `ValidationError` | utils/errors.ts:20 | Input validation failures || `NotFoundError` | utils/errors.ts:32 | Resource not found || `handleAsync()` | utils/errors.ts:45 | Wraps async route handlers || `errorMiddleware()` | middleware/error.ts:10 | Express error handler |
---
## Hooks (React)
| Hook | Location | Does What ||------|----------|-----------|| `useAuth()` | hooks/useAuth.ts | Auth state + login/logout || `useUser()` | hooks/useUser.ts | Current user data || `useDebounce()` | hooks/useDebounce.ts | Debounces value changes || `useLocalStorage()` | hooks/useLocalStorage.ts | Persisted state || `useFetch()` | hooks/useFetch.ts | Data fetching with loading/error |
---
## Components (React)
| Component | Location | Does What ||-----------|----------|-----------|| `Button` | components/Button.tsx | Styled button with variants || `Input` | components/Input.tsx | Form input with validation || `Modal` | components/Modal.tsx | Dialog overlay || `Toast` | components/Toast.tsx | Notification popup || `Spinner` | components/Spinner.tsx | Loading indicator |

# Code Index
*Last updated: [timestamp]**Run `/update-code-index` to regenerate*
## Quick Reference
| Category | Count | Location ||----------|-------|----------|| Date/Time | 5 functions | src/utils/dates.ts || Validation | 8 functions | src/utils/validate.ts || API Clients | 12 functions | src/api/*.ts || Auth | 6 functions | src/auth/*.ts |
---
## Date/Time Operations
| Function | Location | Does What | Params ||----------|----------|-----------|--------|| `formatDate()` | utils/dates.ts:15 | Formats Date → "Jan 15, 2024" | `(date: Date, format?: string)` || `formatRelative()` | utils/dates.ts:32 | Formats Date → "2 days ago" | `(date: Date)` || `parseDate()` | utils/dates.ts:48 | Parses string → Date | `(str: string, format?: string)` || `isExpired()` | auth/tokens.ts:22 | Checks if timestamp past now | `(timestamp: number)` || `addDays()` | utils/dates.ts:61 | Adds days to date | `(date: Date, days: number)` |
---
## Validation
| Function | Location | Does What | Params ||----------|----------|-----------|--------|| `isEmail()` | utils/validate.ts:10 | Validates email format | `(email: string)` || `isPhone()` | utils/validate.ts:25 | Validates phone with country | `(phone: string, country?: string)` || `isURL()` | utils/validate.ts:42 | Validates URL format | `(url: string)` || `isUUID()` | utils/validate.ts:55 | Validates UUID v4 | `(id: string)` || `sanitizeHTML()` | utils/sanitize.ts:12 | Strips XSS from input | `(html: string)` || `sanitizeSQL()` | utils/sanitize.ts:28 | Escapes SQL special chars | `(input: string)` |
---
## String Operations
| Function | Location | Does What | Params ||----------|----------|-----------|--------|| `slugify()` | utils/strings.ts:8 | Converts to URL slug | `(str: string)` || `truncate()` | utils/strings.ts:20 | Truncates with ellipsis | `(str: string, len: number)` || `capitalize()` | utils/strings.ts:32 | Capitalizes first letter | `(str: string)` || `pluralize()` | utils/strings.ts:40 | Adds s/es correctly | `(word: string, count: number)` |
---
## API Clients
| Function | Location | Does What | Returns ||----------|----------|-----------|---------|| `fetchUser()` | api/users.ts:15 | GET /users/:id | `Promise<User>` || `fetchUsers()` | api/users.ts:28 | GET /users with pagination | `Promise<User[]>` || `createUser()` | api/users.ts:45 | POST /users | `Promise<User>` || `updateUser()` | api/users.ts:62 | PATCH /users/:id | `Promise<User>` || `deleteUser()` | api/users.ts:78 | DELETE /users/:id | `Promise<void>` |
---
## Error Handling
| Function/Class | Location | Does What ||----------------|----------|-----------|| `AppError` | utils/errors.ts:5 | Base error class with code || `ValidationError` | utils/errors.ts:20 | Input validation failures || `NotFoundError` | utils/errors.ts:32 | Resource not found || `handleAsync()` | utils/errors.ts:45 | Wraps async route handlers || `errorMiddleware()` | middleware/error.ts:10 | Express error handler |
---
## Hooks (React)
| Hook | Location | Does What ||------|----------|-----------|| `useAuth()` | hooks/useAuth.ts | Auth state + login/logout || `useUser()` | hooks/useUser.ts | Current user data || `useDebounce()` | hooks/useDebounce.ts | Debounces value changes || `useLocalStorage()` | hooks/useLocalStorage.ts | Persisted state || `useFetch()` | hooks/useFetch.ts | Data fetching with loading/error |
---
## Components (React)
| Component | Location | Does What ||-----------|----------|-----------|| `Button` | components/Button.tsx | Styled button with variants || `Input` | components/Input.tsx | Form input with validation || `Modal` | components/Modal.tsx | Dialog overlay || `Toast` | components/Toast.tsx | Notification popup || `Spinner` | components/Spinner.tsx | Loading indicator |

File Header Format

Every file should have a summary header:

TypeScript/JavaScript

typescript

/** * @file User authentication utilities * @description Handles login, logout, session management, and token refresh. * * Key exports: * - login(email, password) - Authenticates user, returns tokens * - logout() - Clears session and tokens * - refreshToken() - Gets new access token * - validateSession() - Checks if session is valid * * @see src/api/auth.ts for API endpoints * @see src/hooks/useAuth.ts for React hook */
import { ... } from '...';

/** * @file User authentication utilities * @description Handles login, logout, session management, and token refresh. * * Key exports: * - login(email, password) - Authenticates user, returns tokens * - logout() - Clears session and tokens * - refreshToken() - Gets new access token * - validateSession() - Checks if session is valid * * @see src/api/auth.ts for API endpoints * @see src/hooks/useAuth.ts for React hook */
import { ... } from '...';

Python

python

"""User authentication utilities.
Handles login, logout, session management, and token refresh.
Key exports:    - login(email, password) - Authenticates user, returns tokens    - logout() - Clears session and tokens    - refresh_token() - Gets new access token    - validate_session() - Checks if session is valid
See Also:    - src/api/auth.py for API endpoints    - src/services/user.py for user operations"""
from typing import ...

"""User authentication utilities.
Handles login, logout, session management, and token refresh.
Key exports:    - login(email, password) - Authenticates user, returns tokens    - logout() - Clears session and tokens    - refresh_token() - Gets new access token    - validate_session() - Checks if session is valid
See Also:    - src/api/auth.py for API endpoints    - src/services/user.py for user operations"""
from typing import ...

Function Documentation

Every function needs a one-line summary:

TypeScript

typescript

/** * Formats a date into a human-readable relative string. * Examples: "2 minutes ago", "yesterday", "3 months ago" */export function formatRelative(date: Date): string {  // ...}
/** * Validates email format and checks for disposable domains. * Returns true for valid non-disposable emails. */export function isValidEmail(email: string): boolean {  // ...}

/** * Formats a date into a human-readable relative string. * Examples: "2 minutes ago", "yesterday", "3 months ago" */export function formatRelative(date: Date): string {  // ...}
/** * Validates email format and checks for disposable domains. * Returns true for valid non-disposable emails. */export function isValidEmail(email: string): boolean {  // ...}

Python

python

def format_relative(date: datetime) -> str:    """Formats a date into a human-readable relative string.
    Examples: "2 minutes ago", "yesterday", "3 months ago"    """    ...
def is_valid_email(email: str) -> bool:    """Validates email format and checks for disposable domains.
    Returns True for valid non-disposable emails.    """    ...

def format_relative(date: datetime) -> str:    """Formats a date into a human-readable relative string.
    Examples: "2 minutes ago", "yesterday", "3 months ago"    """    ...
def is_valid_email(email: str) -> bool:    """Validates email format and checks for disposable domains.
    Returns True for valid non-disposable emails.    """    ...

Check Before Write Process

Before Creating ANY New Function

┌─────────────────────────────────────────────────────────────────┐│  BEFORE WRITING NEW CODE                                        ││  ─────────────────────────────────────────────────────────────  ││                                                                 ││  1. DESCRIBE what you need in plain English                     ││     "I need to format a date as relative time"                  ││                                                                 ││  2. CHECK CODE_INDEX.md                                         ││     Search for: date, time, format, relative                    ││     → Found: formatRelative() in utils/dates.ts                 ││                                                                 ││  3. EVALUATE if existing code works                             ││     - Does it do what I need? → Use it                          ││     - Close but not quite? → Extend it                          ││     - Nothing suitable? → Create new, update index              ││                                                                 ││  4. If extending, check for breaking changes                    ││     - Add optional params, don't change existing behavior       ││     - Update tests for new functionality                        │└─────────────────────────────────────────────────────────────────┘

┌─────────────────────────────────────────────────────────────────┐│  BEFORE WRITING NEW CODE                                        ││  ─────────────────────────────────────────────────────────────  ││                                                                 ││  1. DESCRIBE what you need in plain English                     ││     "I need to format a date as relative time"                  ││                                                                 ││  2. CHECK CODE_INDEX.md                                         ││     Search for: date, time, format, relative                    ││     → Found: formatRelative() in utils/dates.ts                 ││                                                                 ││  3. EVALUATE if existing code works                             ││     - Does it do what I need? → Use it                          ││     - Close but not quite? → Extend it                          ││     - Nothing suitable? → Create new, update index              ││                                                                 ││  4. If extending, check for breaking changes                    ││     - Add optional params, don't change existing behavior       ││     - Update tests for new functionality                        │└─────────────────────────────────────────────────────────────────┘

Decision Tree

Need new functionality        │        ▼Check CODE_INDEX.md for similar        │        ├─► Found exact match ──────► USE IT        │        ├─► Found similar ──────────► Can it be extended?        │                                   │        │                    ┌──────────────┴──────────────┐        │                    ▼                             ▼        │               Yes: Extend                   No: Create new        │               (add params)                  (update index)        │        └─► Nothing found ──────────► Create new (update index)

Need new functionality        │        ▼Check CODE_INDEX.md for similar        │        ├─► Found exact match ──────► USE IT        │        ├─► Found similar ──────────► Can it be extended?        │                                   │        │                    ┌──────────────┴──────────────┐        │                    ▼                             ▼        │               Yes: Extend                   No: Create new        │               (add params)                  (update index)        │        └─► Nothing found ──────────► Create new (update index)

Common Duplication Patterns

Pattern 1: Utility Function Reimplementation

❌ Bad: Creating validateEmail() when isEmail() exists

typescript

// DON'T: This already exists as isEmail()function validateEmail(email: string): boolean {  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);}

// DON'T: This already exists as isEmail()function validateEmail(email: string): boolean {  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);}

✅ Good: Check index first, use existing

Pattern 2: Slightly Different Versions

❌ Bad: Multiple date formatters with slight variations

typescript

// In file Afunction formatDate(d: Date) { return d.toLocaleDateString(); }
// In file Bfunction displayDate(d: Date) { return d.toLocaleDateString('en-US'); }
// In file Cfunction showDate(d: Date) { return d.toLocaleDateString('en-US', { month: 'short' }); }

// In file Afunction formatDate(d: Date) { return d.toLocaleDateString(); }
// In file Bfunction displayDate(d: Date) { return d.toLocaleDateString('en-US'); }
// In file Cfunction showDate(d: Date) { return d.toLocaleDateString('en-US', { month: 'short' }); }

✅ Good: One function with options

typescript

// utils/dates.tsfunction formatDate(d: Date, options?: { locale?: string; format?: 'short' | 'long' }) {  const locale = options?.locale ?? 'en-US';  const formatOpts = options?.format === 'short'    ? { month: 'short', day: 'numeric' }    : { month: 'long', day: 'numeric', year: 'numeric' };  return d.toLocaleDateString(locale, formatOpts);}

// utils/dates.tsfunction formatDate(d: Date, options?: { locale?: string; format?: 'short' | 'long' }) {  const locale = options?.locale ?? 'en-US';  const formatOpts = options?.format === 'short'    ? { month: 'short', day: 'numeric' }    : { month: 'long', day: 'numeric', year: 'numeric' };  return d.toLocaleDateString(locale, formatOpts);}

Pattern 3: Inline Logic That Should Be Extracted

❌ Bad: Same validation logic scattered across files

typescript

// In signup.tsif (!email || !email.includes('@') || email.length < 5) { ... }
// In profile.tsif (!email || !email.includes('@') || email.length < 5) { ... }
// In invite.tsif (!email || !email.includes('@') || email.length < 5) { ... }

// In signup.tsif (!email || !email.includes('@') || email.length < 5) { ... }
// In profile.tsif (!email || !email.includes('@') || email.length < 5) { ... }
// In invite.tsif (!email || !email.includes('@') || email.length < 5) { ... }

✅ Good: Extract once, import everywhere

typescript

// utils/validate.tsexport const isEmail = (email: string) =>  email && email.includes('@') && email.length >= 5;
// Everywhere elseimport { isEmail } from '@/utils/validate';if (!isEmail(email)) { ... }

// utils/validate.tsexport const isEmail = (email: string) =>  email && email.includes('@') && email.length >= 5;
// Everywhere elseimport { isEmail } from '@/utils/validate';if (!isEmail(email)) { ... }

Periodic Audit

Run /audit-duplicates periodically to catch semantic overlap:

Audit Checklist

Utility functions: Any functions doing similar things?
API calls: Multiple ways to fetch same data?
Validation: Scattered inline validation logic?
Error handling: Inconsistent error patterns?
Components: Similar UI components that could merge?
Hooks: Custom hooks with overlapping logic?

Audit Output Format

markdown

## Duplicate Audit - [DATE]
### 🔴 High Priority (Merge These)
1. **Date formatting** - 3 similar functions found   - `formatDate()` in utils/dates.ts   - `displayDate()` in components/Header.tsx   - `showDate()` in pages/Profile.tsx   - **Action:** Consolidate into utils/dates.ts
2. **Email validation** - Inline logic in 5 files   - signup.ts:42   - profile.ts:28   - invite.ts:15   - settings.ts:67   - admin.ts:33   - **Action:** Extract to utils/validate.ts
### 🟡 Medium Priority (Consider Merging)
1. **User fetching** - 2 different patterns   - `fetchUser()` in api/users.ts   - `getUser()` in services/user.ts   - **Action:** Decide on one pattern
### 🟢 Low Priority (Monitor)
1. **Button components** - 3 variants exist   - May be intentional for different use cases   - **Action:** Document the differences

## Duplicate Audit - [DATE]
### 🔴 High Priority (Merge These)
1. **Date formatting** - 3 similar functions found   - `formatDate()` in utils/dates.ts   - `displayDate()` in components/Header.tsx   - `showDate()` in pages/Profile.tsx   - **Action:** Consolidate into utils/dates.ts
2. **Email validation** - Inline logic in 5 files   - signup.ts:42   - profile.ts:28   - invite.ts:15   - settings.ts:67   - admin.ts:33   - **Action:** Extract to utils/validate.ts
### 🟡 Medium Priority (Consider Merging)
1. **User fetching** - 2 different patterns   - `fetchUser()` in api/users.ts   - `getUser()` in services/user.ts   - **Action:** Decide on one pattern
### 🟢 Low Priority (Monitor)
1. **Button components** - 3 variants exist   - May be intentional for different use cases   - **Action:** Document the differences

Vector DB Integration (Optional)

For large codebases (100+ files), add vector search:

Setup with ChromaDB

python

# scripts/index_codebase.pyimport chromadbfrom chromadb.utils import embedding_functions
# Initializeclient = chromadb.PersistentClient(path="./.chroma")ef = embedding_functions.DefaultEmbeddingFunction()collection = client.get_or_create_collection("code_index", embedding_function=ef)
# Index a functioncollection.add(    documents=["Formats a date into human-readable relative string like '2 days ago'"],    metadatas=[{"function": "formatRelative", "file": "utils/dates.ts", "line": 32}],    ids=["formatRelative"])
# Search before writingresults = collection.query(    query_texts=["format date as relative time"],    n_results=5)# Returns: formatRelative in utils/dates.ts - 0.92 similarity

# scripts/index_codebase.pyimport chromadbfrom chromadb.utils import embedding_functions
# Initializeclient = chromadb.PersistentClient(path="./.chroma")ef = embedding_functions.DefaultEmbeddingFunction()collection = client.get_or_create_collection("code_index", embedding_function=ef)
# Index a functioncollection.add(    documents=["Formats a date into human-readable relative string like '2 days ago'"],    metadatas=[{"function": "formatRelative", "file": "utils/dates.ts", "line": 32}],    ids=["formatRelative"])
# Search before writingresults = collection.query(    query_texts=["format date as relative time"],    n_results=5)# Returns: formatRelative in utils/dates.ts - 0.92 similarity

Setup with LanceDB (Lighter)

python

# scripts/index_codebase.pyimport lancedb
db = lancedb.connect("./.lancedb")
# Create tabledata = [    {"function": "formatRelative", "file": "utils/dates.ts", "description": "Formats date as relative time"},    {"function": "isEmail", "file": "utils/validate.ts", "description": "Validates email format"},]table = db.create_table("code_index", data)
# Searchresults = table.search("validate email address").limit(5).to_list()

# scripts/index_codebase.pyimport lancedb
db = lancedb.connect("./.lancedb")
# Create tabledata = [    {"function": "formatRelative", "file": "utils/dates.ts", "description": "Formats date as relative time"},    {"function": "isEmail", "file": "utils/validate.ts", "description": "Validates email format"},]table = db.create_table("code_index", data)
# Searchresults = table.search("validate email address").limit(5).to_list()

When to Use Vector DB

Claude Instructions

At Session Start

Read CODE_INDEX.md if it exists
Note the categories and key functions available
Keep this context for the session

Before Writing New Code

Pause and check: "Does something like this exist?"
Search CODE_INDEX.md for similar capabilities
If unsure, search the codebase: grep -r "functionName\|similar_term" src/
Only create new if confirmed nothing suitable exists

After Writing New Code

Immediately update CODE_INDEX.md
Add file header if new file
Add function docstring
Commit index update with code

When User Says "Add X functionality"

Before implementing, let me check if we already have something similar...
[Checks CODE_INDEX.md]
Found: `existingFunction()` in utils/file.ts does something similar.Options:1. Use existing function as-is2. Extend it with new capability3. Create new (if truly different use case)
Which approach would you prefer?

Before implementing, let me check if we already have something similar...
[Checks CODE_INDEX.md]
Found: `existingFunction()` in utils/file.ts does something similar.Options:1. Use existing function as-is2. Extend it with new capability3. Create new (if truly different use case)
Which approach would you prefer?

Quick Reference

Update Index Command

Audit Command

File Header Template

typescript

/** * @file [Short description] * @description [What this file does] * * Key exports: * - function1() - [what it does] * - function2() - [what it does] */

/** * @file [Short description] * @description [What this file does] * * Key exports: * - function1() - [what it does] * - function2() - [what it does] */

Function Template

Index Entry Template

Source and attribution

Source:alinaqi/maggyinskills/code-deduplicationat commit72a456e

License: No license

Content belongs to its original authors. SourceWeft indexes it from a public repository.

Report or request removal

Codebase Size	Recommendation
< 50 files	Markdown index only
50-200 files	Markdown + periodic audit
200+ files	Add vector DB
500+ files	Vector DB essential

Code Deduplication

Code Deduplication Skill

Core Philosophy

Code Index Structure

File Header Format

TypeScript/JavaScript

Python

Function Documentation

TypeScript

Python

Check Before Write Process

Before Creating ANY New Function

Decision Tree

Common Duplication Patterns

Pattern 1: Utility Function Reimplementation

Pattern 2: Slightly Different Versions

Pattern 3: Inline Logic That Should Be Extracted

Periodic Audit

Audit Checklist

Audit Output Format

Vector DB Integration (Optional)

Setup with ChromaDB

Setup with LanceDB (Lighter)

When to Use Vector DB

Claude Instructions

At Session Start

Before Writing New Code

After Writing New Code

When User Says "Add X functionality"

Quick Reference

Update Index Command

Audit Command

File Header Template

Function Template

Index Entry Template

Source and attribution

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