# GS1 AI (21) Individual Serial Number Specification
> Extract unit-level serial numbers from 1D and 2D GS1 barcodes for track-and-trace systems.

- **Canonical URL:** https://stanzaapi.com/tools/gs1-decoder/ai/21-serial-number
- **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
AI (21) encodes an individual serial number that uniquely differentiates single items carrying the same GTIN.

## Specification Matrix
| Attribute | Rule |
| --- | --- |
| Max Length | 20 characters |
| Character Set | Alphanumeric (GS1 Set 82) |
| Format | Variable length |

## Standard JSON Response Model
```json
{
  "ai": "21",
  "serialNumber": "SN998812345"
}
```

## Frequently Asked Questions & Edge Cases
### Q: Can AI 21 contain special characters?
**A:** Yes, hyphens, periods, and forward slashes are allowed under GS1 specifications.