The compound effect only works if you capture what you learn. This isn't about creating extensive documentation—it's about writing down just enough that future sessions (and future you) benefit.
🤔 Good vs. Bad Documentation
Let's see the difference:
| ❌ Not Helpful | ✅ Actually Useful |
|---|---|
| "Fixed bugs" | "Fixed: Timer was resetting on page refresh. Added localStorage save in startTimer()" |
| "Added features" | "Added task naming and 7-day history view. Uses array of {name, duration, date} objects" |
| "Made changes to code" | "Switched from setInterval to requestAnimationFrame for smoother timer. Prevents drift over long sessions" |
| "Updated stuff" | "Used localStorage instead of sessionStorage so timer persists across browser closes. 5MB limit noted" |
✨ The Difference
Good documentation answers: What changed + Why it matters + How it works. Future you (and future Claude) need all three.
📋 What to Document
At the end of each significant session, capture:
"Added user authentication with login and logout functionality."
"Used localStorage for session tokens because we don't need a backend yet."
"The form wasn't submitting because we forgot to prevent default. Added e.preventDefault()."
"Next time, validate form inputs before submission."
🎯 The End-of-Session Ritual
Make documentation automatic by asking Claude at the end of each session:
This takes 5 minutes but pays dividends in every future session.
📖 Complete Session Documentation Example
Here's what good end-of-session documentation looks like:
What We Built:
• Task naming input field
• 7-day history view showing past tasks
• localStorage persistence for history
Decisions Made:
• Store history as array of objects: {name, duration, date, id}
• Use ISO date strings for easy sorting
• UUID for IDs (not auto-increment) to avoid conflicts
• Limit history to 100 items to prevent localStorage bloat
Problems Solved:
• History wasn't sorted chronologically → Added .sort() by date
• Old entries weren't pruning → Added cleanup function keeping newest 100
• Date display was ugly → Used toLocaleDateString()
What's Next:
• Phase 3: Visual breakdown (pie/bar chart)
• Maybe: Edit past task names
• Maybe: Export to CSV
Patterns Established:
• Always generate UUID for any item that might be edited later
• Keep data cleanup automatic (prune on every add)
• Format dates for display, store as ISO strings
✅ Why This Works
Six months from now, you can read this and understand: what exists, why it's built that way, and what patterns to follow when adding more features.
✏️ Practice: Document a Session
Think about the last thing you built (or will build):
🎯 Your Session Documentation
Not "added features" but "added X which does Y"
List 2-3 specific things that were added or changed.
What choices did you make? Why that approach over alternatives?
Document 1-2 decisions that future you should know about.
What didn't work at first? What was the fix?
Capture 1-2 issues and their solutions.
What approach should you follow next time?
Note 1-2 patterns worth repeating.
Actually create the documentation. Use the format above, or ask Claude: "Document this session with what we built, decisions, problems solved, and patterns."
⚡ Pro Tip: Document Immediately
Document at the end of the session while it's fresh. Waiting until "later" means you forget the why behind decisions. Five minutes now saves an hour later.
📍 Where to Put It
- Claude.md: Project context, patterns, preferences—things Claude should know
- README.md: User-facing documentation—what the project does, how to use it
- CHANGELOG.md: Session-by-session log of changes (optional but useful)
- Comments in code: Explain non-obvious decisions inline
Quick guide:
| Type of Info | Where It Goes |
|---|---|
| Project purpose, tech stack, patterns | Claude.md - Claude reads this every session |
| How to use the app, features, setup | README.md - For users (including future you) |
| Session-by-session changes | CHANGELOG.md - Timeline of what happened when |
| Why a specific line of code exists | Code comments - Inline explanations |
💡 Future You Will Thank Present You
In a week, you won't remember why you did things a certain way. A single sentence explaining "did X because Y" can save an hour of confusion later.
✅ Documentation Checklist
Before ending a session, ask yourself:
- If I came back in a month, would I understand what I built?
- If I asked Claude to continue this tomorrow, would it have enough context?
- Are any non-obvious decisions explained somewhere?
- Is the current status clear?
If yes to all, you're good. If not, spend 5 minutes fixing it.
End-of-Session Quick Check
📚 Resources & Further Reading
- Compound Engineering (Every.to) Why the compound step matters
- Write the Docs: Beginner's Guide General documentation principles
💭 Pause & Reflect
Before moving on, take a moment to consider:
- What's your current approach to documentation? Do you do it? Skip it?
- Can you think of a time when you wished you'd documented something?
- What would make documentation feel less like a chore and more automatic?
🎯 Documentation Habits Formed
You know what to capture and where. Next: experiencing the compounding effect firsthand.
Topic 3.3 Complete • Up Next: 3.4 – Experiencing Compounding