# GS1 AI (01) Global Trade Item Number (GTIN) & Mod-10 Checksum
> Instant Modulo-10 checksum validation and structure decomposition for GS1 AI (01) GTIN barcodes.

- **Canonical URL:** https://stanzaapi.com/tools/gs1-decoder/ai/01-gtin
- **Governing Standard:** GS1 General Specifications & AI Syntax (GS1 Global Standards Architecture)
- **Latency:** <1ms Edge
- **Privacy:** In-memory execution only (zero data stored or logged)

## Technical Overview & Governing Rules
The GTIN is the 14-digit universal identifier for trade items at all packaging levels. The final digit is a Modulo-10 check digit calculated by alternating weights of 3 and 1.

## Specification Matrix
| Step | Calculation | Rule |
| --- | --- | --- |
| Weight Assignment | Multiply digits from right to left (excluding check digit) by 3 and 1 alternating | Weights: 3, 1, 3, 1... |
| Summation | Add all weighted products | Total sum |
| Modulo-10 Check | (10 - (Sum % 10)) % 10 | Matches check digit |

## Standard JSON Response Model
```json
{
  "ai": "01",
  "gtin": "00012345678905",
  "checkDigit": 5,
  "valid": true
}
```

## Frequently Asked Questions & Edge Cases
### Q: How is GTIN-12 (UPC-A) represented in GTIN-14?
**A:** Two leading zeroes are prepended to standard 12-digit UPCs to form the 14-digit GTIN.