MQTT data - 'value_json' is undefined - JSON checks

Configuration
,
1

How do I get this data into HA?

After searching I have reviewed the below discussion and I see similarity in the issue but I remain unclear as to how to resolve my issue, particularly the lack of quotes around some of the returns:
Template variable error: ‘value_json’ is undefined - mqtt

The MQTT broker is receiving the following input:

image
image1102×1203 67.5 KB

{
    "stnname": "WiFiLogger",
    "stnmod": 16,
    "ver": 3.15,
    "mac": "70:B8:F6:9B:E6:14",
    "apmac": "70:B8:F6:9B:E6:15",
    "ip": "192.168.9.79",
    "ssid": "AsylumIOT",
    "rssi": -49,
    "wifimod": 0,
    "lastboot": 1716237779,
    "uptime": 2567,
    "wflver": "2.42",
    "loctime": 1716225940,
    "utctime": 1716240340,
    "tzone": 10,
    "units": 4,
    "conlati": 424,
    "conlongi": -715,
    "wfllati": -300,
    "wfllongi": -300,
    "tempout": "71.5",
    "humout": "64",
    "tempin": "66.3",
    "humin": "50",
    "windspd": "0.0",
    "winddir": "138",
    "windavg2": "0.0",
    "windavg10": "0.0",
    "gust": "0.0",
    "gustdir": "130",
    "bar": "29.950",
    "bartr": "-20",
    "dew": "59",
    "cdew": "58.7",
    "chill": "72",
    "heat": "72",
    "thsw": "---",
    "uv": "---",
    "solar": "---",
    "rainr": "0.00000",
    "storm": "0.00000",
    "rain15": "0.00000",
    "rain1h": "0.00000",
    "raind": "0.00000",
    "rain24": "0.00000",
    "rainmon": "2.53000",
    "rainyear": "18.10000",
    "etday": "0.000",
    "etmon": "0.00",
    "etyear": "0.00",
    "xt": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "xlt": [
        "---",
        "---",
        "---",
        "---"
    ],
    "xst": [
        "---",
        "---",
        "---",
        "---"
    ],
    "xh": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "xsm": [
        "---",
        "---",
        "---",
        "---"
    ],
    "xlw": [
        "---",
        "---",
        "---",
        "0"
    ],
    "bat": "4.49",
    "trbat": "0",
    "foreico": "3",
    "forrule": "187",
    "sunrt": "5:20",
    "sunst": "20:07",
    "hlbar": [
        "29.947",
        "30.038",
        "17:17",
        "8:22",
        "30.342",
        "29.468",
        "30.565",
        "28.889"
    ],
    "hlwind": [
        "---",
        "7.0",
        "---",
        "11:48",
        "15.0",
        "---",
        "34.0",
        "---"
    ],
    "hltempin": [
        "62.6",
        "66.3",
        "6:37",
        "17:24",
        "72.7",
        "58.5",
        "72.7",
        "58.5"
    ],
    "hlhumin": [
        "43",
        "52",
        "10:25",
        "13:25",
        "52",
        "27",
        "52",
        "19"
    ],
    "hltempout": [
        "49.0",
        "73.4",
        "1:37",
        "15:15",
        "82.8",
        "37.4",
        "82.8",
        "9.9"
    ],
    "hlhumout": [
        "58",
        "97",
        "15:16",
        "6:08",
        "97",
        "25",
        "98",
        "17"
    ],
    "hldew": [
        "48",
        "59",
        "1:11",
        "12:36",
        "62",
        "33",
        "62",
        "-1"
    ],
    "hlchil": [
        "49",
        "---",
        "1:19",
        "---",
        "---",
        "37",
        "---",
        " 8"
    ],
    "hlheat": [
        "---",
        "74",
        "---",
        "15:03",
        "82",
        "---",
        "82",
        "---"
    ],
    "hlthsw": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlsolar": [
        "---",
        "0",
        "---",
        "---",
        "0",
        "---",
        "0",
        "---"
    ],
    "hluv": [
        "---",
        "0.0",
        "---",
        "---",
        "0.0",
        "---",
        "0.0",
        "---"
    ],
    "hlrainr": [
        "0.000",
        "0.000",
        "---",
        "---",
        "0.930",
        "---",
        "3.890",
        "---"
    ],
    "hlxt0": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxt1": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxt2": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxt3": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxt4": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxt5": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxt6": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxh0": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxh1": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxh2": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxh3": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxh4": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxh5": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxh6": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxst0": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxst1": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxst2": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxst3": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxlt0": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxlt1": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxlt2": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxlt3": [
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxsm0": [
        "---",
        "---",
        "0:00",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxsm1": [
        "---",
        "---",
        "0:00",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxsm2": [
        "---",
        "---",
        "0:00",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxsm3": [
        "---",
        "---",
        "0:00",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxlw0": [
        "---",
        "---",
        "0:00",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxlw1": [
        "---",
        "---",
        "0:00",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxlw2": [
        "---",
        "---",
        "0:00",
        "---",
        "---",
        "---",
        "---",
        "---"
    ],
    "hlxlw3": [
        "---",
        "---",
        "0:00",
        "---",
        "---",
        "---",
        "---",
        "---"
    ]
}
QoS: 2 - Retain: false

The above passes JSON Checker - The JSON Validator and Formatter

image
image1796×278 14.6 KB

Yet the below template still produces the ‘value_json’ is undefined error.

image
image1607×609 37.5 KB

2

The “lack of quotes” isn’t the issue. That is how numbers are correctly represented in json data.

You cant use the template editor to test your config like that. The template editor has no method of connecting to your mqtt broker and returning a result like the mqtt integration does. All it does is evaluate templates, so value_json does not exist in the template editor unless you manually define it. e.g.

{% value_json = <your_json_data_here> %}
3

Looking at your data your mqtt sensor config appears correct. Just try it. Though I would add the following options:

      device_class: temperature  # -> nice icon and ability to change units from the UI
      state_class: measurement # -> long term statistics for history older than 10 days
4

Thanks for the recommendation, but still returning “unknown”.

mqtt:
  sensor:
  - name: "Davis Vantage Pro - Air Temp - Outside "
    state_topic: "/davis/wflexpj.json"
    unit_of_measurement: "°F"
    device_class: temperature  # -> nice icon and ability to change units from the UI
    state_class: measurement # -> long term statistics for history older than 10 days
    value_template: "{{ value_json.tempout }}"

image
image1964×1104 92.8 KB

Any thoughts on where to go from here?

5

This is not correct:

Delete the leading / from your topic:

state_topic: "davis/wflexpj.json"

I highly recommend you download MQTT Explorer (free). It lets you look at topics and values in your broker easily.

6

I doubt your topic is named davis/wflexpj.json. The .json is not normal.

7

I initially mentioned that too but deleted it when I saw this:

0b6df6c04c20cbb83f08a192ab20cb554c743806
0b6df6c04c20cbb83f08a192ab20cb554c743806788×758 33.9 KB

I think that really is the topic.

2 Likes
8

weird

9

Thank you. Deleting the ‘/’ and it is all accessible.

image
image2255×1188 291 KB

Re: MQTT Explorer - Got it - using it

1 Like
10

currently i think i am having a similar issues "

e[31m2025-11-09 00:25:53.337 ERROR (MainThread) [homeassistant.helpers.template] Template variable error: 'value_json' is undefined when rendering '{{ value_json.current }}'e[0m
e[31m2025-11-09 00:25:53.338 ERROR (MainThread) [homeassistant.helpers.template] Template variable error: 'value_json' is undefined when rendering '{{ value_json.state }}'e[0m
e[31m2025-11-09 00:25:53.338 ERROR (MainThread) [homeassistant.helpers.template] Error parsing value: 'value_json' is undefined (value: , template: {{ value_json.state }})e[0m
e[31m2025-11-09 00:25:53.339 ERROR (MainThread) [homeassistant.helpers.template] Template variable error: 'value_json' is undefined when rendering '{{ value_json.energy }}'e[0m
e[33m2025-11-09 00:25:53.339 WARNING (MainThread) [homeassistant.components.mqtt.update] Unable to process payload '' for topic zigbee2mqtt/Plug (router), with value template 'Template<template=({"latest_version":"{{ value_json['update']['latest_version'] }}","installed_version":"{{ value_json['update']['installed_version'] }}","update_percentage":{{ value_json['update'].get('progress', 'null') }},"in_progress":{{ (value_json['update']['state'] == 'updating')|lower }}}) renders=2>'e[0m
e[31m2025-11-09 00:25:53.340 ERROR (MainThread) [homeassistant.helpers.template] Template variable error: 'value_json' is undefined when rendering '{{ value_json.power_on_behavior }}'e[0m
e[31m2025-11-09 00:25:53.340 ERROR (MainThread) [homeassistant.helpers.template] Error parsing value: 'value_json' is undefined (value: , template: {{ value_json.power_on_behavior }})e[0m
e[31m2025-11-09 00:25:53.340 ERROR (MainThread) [homeassistant.helpers.template] Template variable error: 'value_json' is undefined when rendering '{{ value_json.voltage }}'e[0m
e[31m2025-11-09 00:25:53.340 ERROR (MainThread) [homeassistant.helpers.template] Template variable error: 'value_json' is undefined when rendering '{{ value_json.power }}'e[0m

any idea what i would need to do ?

11

You already have a topic about this. Please don’t cross post to year old topics.