Encode JSON Data in a QR Code

QR Codes for JSON Data

Encoding JSON data in a QR code enables machine-readable data transfer without network connectivity. This is useful for device provisioning, configuration sharing, and IoT scenarios.

Basic JSON QR Code

Any valid JSON can be encoded as a QR code:

{"id":"device-001","config":{"mode":"production","interval":30}}

The QR scanner reads the raw text, and the receiving application parses it as JSON.

Size Optimization

JSON is verbose by nature, so minimizing data size is critical for QR codes:

1. Minify the JSON — Remove all whitespace:

{"id":"device-001","config":{"mode":"production","interval":30}}

2. Use short key names — Replace descriptive keys with abbreviated ones:

{"i":"d001","c":{"m":"prod","t":30}}

3. Remove unnecessary fields — Only include data that the receiving application actually needs.

4. Use arrays instead of objects — When the schema is known on both sides:

["d001","prod",30]

Data Capacity Planning

For a Version 10 QR code (57x57 modules) with Medium error correction:

Content Type	Approximate Capacity
ASCII JSON	~652 characters
UTF-8 JSON	~450 characters
Numeric-heavy JSON	~1,000+ characters

Validation Strategy

Since QR codes can be damaged or partially unreadable, always validate the parsed JSON on the receiving end:

1. Check that the scanned text is valid JSON (JSON.parse())
2. Validate against an expected schema
3. Verify required fields are present
4. Check data types and value ranges

Alternative: Base64-Encoded Binary

For larger datasets, consider encoding binary formats (MessagePack, CBOR, Protocol Buffers) as Base64 within the QR code. This can reduce data size by 30-50% compared to plain JSON.

Security Considerations

• Never trust QR-scanned JSON without validation
• Sanitize string values to prevent injection attacks
• Use schema validation (JSON Schema) for critical applications
• Consider signing the JSON payload with HMAC if integrity is important