# error: json: cannot unmarshal number 99999999999999999999 into Go value of type int64

- **ID:** `go/encoding-json-unmarshal-number-overflow`
- **Domain:** go
- **Category:** data_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

A JSON number exceeds the range of the target Go integer type, causing overflow.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 1.20 | active | — | — |
| 1.21 | active | — | — |

## Workarounds

1. **Use json.Number or big.Int for large numbers** (90% success)
   ```
   var num json.Number
if err := json.Unmarshal(data, &num); err != nil { return err }
intVal, _ := num.Int64()
   ```

## Dead Ends

- **Using float64 to store large numbers** — May lose precision for very large integers; use big.Int or string. (50% fail)