Claude Opus 4.8 vs GPT-5.6 Luna for vibe coding

## Top 3 Improvements

- **Validate input**: handle empty/negative/non-numeric bills to avoid showing misleading `£NaN` results.
- **Show tip amount separately**: users want to see the tip, not just the total.
- **Label controls**: add accessible labels so the fields' purpose is clear.

## Updated File

```html
<label for="bill">Bill amount (£):</label>
<input id="bill" type="number">
<label for="pct">Tip %:</label>
<select id="pct"><option>10</option><option>15</option><option>20</option></select>
<button onclick="calc()">Go</button>
<p id="ou…

- Add explicit labels for bill and percentage controls to improve accessibility.
- Validate bill input and constrain it to nonnegative currency values.
- Replace fragile implicit element globals with explicit DOM lookups and `textContent`.

```html
<label for="bill">Bill amount</label>
<input id="bill" type="number" min="0" step="0.01" required>
<label for="pct">Tip percentage</label>
<select id="pct">
  <option>10</option>
  <option>15</option>
  <option>20</option>
</select>
<button onclick="calc()">Go</button>
<p id="out"></p>
<script>
funct…