add-feature

name	add-feature
description	Add new functionality by understanding existing patterns and dependencies before writing code. Locates where the feature belongs, studies conventions, implements following precedent, then verifies integration. Use when asked to add a feature, flag, endpoint, component, or module.
compatibility	Requires tokenlean CLI tools (npm i -g tokenlean) and git

Add Feature

Add functionality by understanding existing code before writing new code.

Workflow

Locate → Understand → Implement → Integrate → Verify

1. Locate

Find where the feature belongs:

tl parallel "tl structure" "tl entry" "tl example <pattern>"

2. Understand

Before writing a single line:

tl parallel \
  "symbols=tl symbols <file>" \
  "style=tl style" \
  "deps=tl deps <file>" \
  "exports=tl exports <file>"

3. Implement

# Extending an existing file?
tl snippet <function> <file>   # Read just the function you're modifying

# New file?
# Follow conventions from tl style, place per tl structure

# Adding a dependency?
tl npm <package>           # Check size, health, and download stats first

4. Integrate

Wire it into the existing system:

tl parallel \
  "impact=tl impact <modified-file>" \
  "guard=tl guard" \
  "diff=tl diff --breaking"

5. Verify

tl parallel "test=tl run '<test command>'" "testmap=tl test-map <file>"

Decision tree

Feature request → Does similar functionality exist?
  ├─ Yes (extending) → tl example to find the pattern
  │   → tl symbols on target file
  │   → tl snippet on the function to extend
  │   → Implement following the existing pattern
  ├─ Yes (replacing) → tl impact on what you're replacing
  │   → tl exports to check public API surface
  │   → Implement, update all consumers
  └─ No (greenfield) → tl structure for placement
      → tl style for conventions
      → tl entry to understand how it'll be wired in
      → Implement, then tl guard to check integration

Tips

• Always run tl example before implementing — the codebase almost always has a precedent
• Use tl npm before adding any new dependency — check size and health
• Run tl diff --breaking after modifying any file with exports
• For React/frontend projects, also use tl component on main UI files
• If a file is under 150 lines, just read it directly — tokenlean overhead isn't worth it