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README.md

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+# Vet Label Printer Client
+
+This is a Docker-based MQTT client that listens for print requests, generates vet drug prescription labels, and prints them using a Brother QL printer.
+
+## Setup
+
+1. Configure the environment variables in `.env`:
+   - `MQTT_HOST`: MQTT broker hostname
+   - `MQTT_PORT`: MQTT broker port
+   - `MQTT_TOPIC_SUB`: Topic to subscribe for print requests
+   - `MQTT_TOPIC_PUB_ERRORS`: Topic to publish errors
+   - `PRINTER_DEVICE`: Printer device path (e.g., /dev/usb/lp0)
+   - `PRINTER_MODEL`: Printer model (e.g., QL-800)
+   - `LABEL_SIZE_DEFAULT`: Default label size (e.g., 29x90)
+
+2. Build and run with Docker Compose:
+   ```bash
+   docker-compose up --build
+   ```
+
+## MQTT Message Format
+
+The client subscribes to the configured topic and expects JSON messages like:
+
+```json
+{
+  "template_id": "vet_label",
+  "label_size": "29x90",
+  "variables": {
+    "practice_name": "Many Tears Animal Rescue",
+    "animal_name": "Rosie 468837",
+    "drug_name": "Amoxicillin 50mg",
+    "dosage": "1 tablet twice daily with food",
+    "quantity": "14 tablets",
+    "vet_initials": "Frank Molina"
+  },
+  "test": false
+}
+```
+
+- `template_id`: Identifier for the label template (currently only "vet_label" supported)
+- `label_size`: Size of the label (passed to brother-ql)
+- `variables`: Key-value pairs for label content
+- `test`: If true, saves PNG to `/app/output/` instead of printing
+
+## Error Handling
+
+Any errors during processing are published to the error topic as JSON:
+
+```json
+{
+  "error": "Error message",
+  "original_payload": "{original message}"
+}
+```
+
+## Adding New Templates
+
+To add new label templates, edit `templates.py` and add to the `TEMPLATES` dict.