Include the "Why" in Your Prompts So Claude Makes Better Implementation Decisions

The same instruction produces very different code depending on the motivation behind it. Claude doesn't just follow orders — it makes dozens of small implementation decisions along the way. The "why" guides those decisions.

Compare these two prompts:

❌ "add caching to the getUser method"

✅ "add caching to the getUser method — it's called 50+ times per page
   load and the database query takes 200ms each time, which is making
   the dashboard unusably slow for customers"

The first prompt might add a simple 60-second cache. The second tells Claude this is a performance-critical hot path — so it might use a longer TTL, add cache warming, include cache invalidation when the user updates their profile, and add a comment explaining why the caching exists.

The "why" changes the implementation in meaningful ways:

❌ "add input validation to the checkout form"
✅ "add input validation to the checkout form — we're getting chargebacks
   from bots submitting fake orders with obviously invalid addresses"

❌ "split this into two files"
✅ "split this into two files — we need to reuse the calculation logic
   in the API and the CLI without duplicating it"

❌ "add error handling"
✅ "add error handling — users see a blank page when the payment
   provider is down, and support gets flooded with tickets"

Each version gives Claude the information to make better choices about how to implement — what edge cases matter, how aggressive to be, what error messages to show, and where the boundaries should be.

This applies to debugging too:

❌ "why is this test failing?"
✅ "this test started failing after we added the new discount feature
   yesterday — it was passing before that PR was merged"

Now Claude knows exactly where to look instead of investigating the entire test in isolation.

The "what" tells Claude the task. The "why" tells Claude how to think about it.

via Claude Code