Setting up MQTT monitoring with Zabbix 6.0(LTS), agent2, mosquitto and zigbee2mqtt

[cgrenier]

Hello
On a Raspberry pi, zigbee2mqtt is sending the results to a local mosquitto instance and zabbix-agent 2 is running with active checks enabled.
On the zabbix server interface, a master item has been created for the Raspberry pi:
- name: zigbee-cgr
- type: Zabbix agent (active)
- key: mqtt.get["","zigbee2mqtt/zigbee-cgr/#"]
- no preprocessing
When I asked for previous values, I can results like
2025-11-17 16:41:58 {"zigbee2mqtt/zigbee-cgr":"{"humidity":48.95,"linkquality":224,"t e mperature":22.17}"}

A dependant item has been created:
- name: Temperature [C]
- type: Dependant Item
- Key: temperature
- Type of information float
- Master item: zigbee-cgr
- Preprocessing: JSONPath $.temperature

Preprocessing failed for: {"zigbee2mqtt/zigbee-cgr":"{"humidity":49.39,"linkquality":232,"t e mperature":21.93}"}
1. Failed: cannot extract value from json by path "$.temperature": no data matches the specified path

I have found another post about MQTT but it wasn't using mosqutto. I also read Ivo_Schooneman_Feeding_Zabbix_with_MQTT_data.pdf without understanding what was broken in my setup.
What should I do to fix it ?

[cgrenier]

Thanks for your help. I have been able to solve it by adding a PreProcessing in the master item.

On the zabbix server interface, a master item for the Raspberry pi is now
- name: zigbee-cgr
- type: Zabbix agent (active)
- key: mqtt.get["","zigbee2mqtt/zigbee-cgr/#"]
- JSONPath Preprocessing $['zigbee2mqtt/zigbee-cgr']

The dependant item is unchanged:
- name: Temperature [C]
- type: Dependant Item
- Key: temperature
- Type of information float
- Master item: zigbee-cgr
- Preprocessing: JSONPath $.temperature

[BP_Vital]

Preprocessing failed for: {"zigbee2mqtt/zigbee-cgr":"{"humidity":49.39,"linkquality":232,"t e mperature":21.93}"}
cannot extract value from json by path "$.temperature"

I'd say fixing template would be faster to include those extra spaces if they appear everywhere,
OR additional custom preprocessing step to convert "t e mperature" -> "temperature" is a shortcut too.

[cgrenier]

Thanks for your reply but the extra spaces only appears in my post on the zabbix forum when I choose "Preview" in the forum (maybe to wrap long line).
Another idea ?

[BP_Vital]

I'm confused by slash symbols in the master item JSON. Maybe try to preprocess string getting rid of them?
Also i suspect $.temperature is not sufficient in that case, you probably need to go deeper into JSON to extract that temperature value.
I usually debug Jsonpath by testing preprocessing with those <IMAGE>
Try to paste raw value you would get from agent and preprocess with different Jsonpath.

[cgrenier]

Thanks for your help. I have been able to solve it by adding a PreProcessing in the master item.

On the zabbix server interface, a master item for the Raspberry pi is now
- name: zigbee-cgr
- type: Zabbix agent (active)
- key: mqtt.get["","zigbee2mqtt/zigbee-cgr/#"]
- JSONPath Preprocessing $['zigbee2mqtt/zigbee-cgr']

The dependant item is unchanged:
- name: Temperature [C]
- type: Dependant Item
- Key: temperature
- Type of information float
- Master item: zigbee-cgr
- Preprocessing: JSONPath $.temperature