Write your first pack

In about ten minutes, this page builds the shelly-plug reference pack from scratch: a Shelly smart plug (Plus, Pro or Gen3) read through its local API, with power, energy and temperature, and an alert when it overheats.

You need Docker, and either a Shelly plug on your network or the captured response below.

1. Look at what the device answers

Shelly’s second-generation devices describe a relay with one call:

curl http://192.168.1.50/rpc/Switch.GetStatus?id=0

{
  "id": 0,
  "source": "HTTP_in",
  "output": true,
  "apower": 8.9,
  "voltage": 237.5,
  "current": 0.069,
  "aenergy": { "total": 6532.2, "by_minute": [45.199, 47.141, 88.397] },
  "temperature": { "tC": 41.3, "tF": 106.3 }
}

Save this answer as shelly-plug/fixtures/status.json: it is the fixture the pack will be tested against, so you can work without the device at hand.

2. The header

Create shelly-plug/pack.yaml:

schema: 1
id: shelly-plug
version: 1.0.0
label: Shelly plug (Gen2+)
summary: Power, energy, voltage and temperature of a Shelly Plus/Pro/Gen3 plug or relay.
examples: [Shelly Plus Plug S, Shelly Pro 1PM]
address_hint: 192.168.1.50
default_port: 80
credentials: [none]

The id decides two names: the monitor type pack.shelly-plug, and the metric prefix dumbmonit_shelly_plug_.

3. One source

A source is one request, always to the device’s own address:

options:
  - key: switch_id
    label: Switch channel
    help: 0 for a plug; 0, 1, 2… for each channel of a multi-channel relay.
    input: number
    default: 0

sources:
  - id: status
    type: http
    path: /rpc/Switch.GetStatus?id={{option.switch_id}}

{{option.switch_id}} is replaced by the monitor’s own setting, shown in the monitor form as Switch channel. The file name of the fixture, status.json, matches the source id.

4. The metrics

Each metric picks a value with a JSONPath expression. Names are written without the prefix:

metrics:
  - name: output_on
    help: 1 when the relay is closed (power flows), 0 when it is open.
    source: status
    json: $.output
  - name: power_watts
    source: status
    json: $.apower
  - name: voltage_volts
    source: status
    json: $.voltage
  - name: current_amperes
    source: status
    json: $.current
  - name: energy_watthours_total
    source: status
    kind: counter
    json: $.aenergy.total
  - name: temperature_celsius
    source: status
    json: $.temperature.tC

output is a boolean: it becomes 1 or 0. The energy total only grows, so it is a counter: charts and rules read it with rate(), and a restart of the plug does not look like a drop.

5. Check it

docker run --rm -v "$PWD:/work" --user "$(id -u)" ghcr.io/selfhostr/dumbmonit:latest \
  pack test /work/shelly-plug --update

ok: shelly-plug 1.0.0 (pack.shelly-plug, 6 metrics, 0 rules)
  wrote /work/shelly-plug/expected.prom

expected.prom shows exactly what the server would store from the fixture:

# TYPE dumbmonit_shelly_plug_power_watts gauge
dumbmonit_shelly_plug_power_watts 8.9
# TYPE dumbmonit_shelly_plug_temperature_celsius gauge
dumbmonit_shelly_plug_temperature_celsius 41.3
…

Read it once. From now on, pack test without --update fails if a change to the pack changes what it extracts, and prints the lines that differ.

6. An alert rule

Rules come with the pack and use its metrics by their full name. The threshold can come from an option, so each plug can have its own:

options:
  # … switch_id, then:
  - key: max_temperature
    label: Temperature alert (°C)
    input: number
    default: 70

rules:
  - name: overheating
    title: Shelly plug overheating
    description: The internal temperature stayed above the limit for five minutes.
    expr: dumbmonit_shelly_plug_temperature_celsius
    op: ">"
    threshold: "{{option.max_temperature}}"
    for: 5m
    severity: warning
    unit: °C

Run pack lint to check the whole file: a rule citing a metric the pack does not produce, an option that does not exist or a path that points elsewhere are reported with where they are.

docker run --rm -v "$PWD:/work:ro" ghcr.io/selfhostr/dumbmonit:latest pack lint /work/shelly-plug

7. Install it

With an API token that has the write scope:

curl -H 'Authorization: Bearer dmt_…' -H 'Content-Type: application/yaml' \
  --data-binary @shelly-plug/pack.yaml https://localhost:8080/api/packs

Open Monitors → Add monitor: Shelly plug (Gen2+) is in the list. Add your plug with its address; the first poll comes within a minute, and the Shelly plug overheating rule is in Alerts → Rules.

To publish a new version, raise version, run pack test, and install it again: the extraction is replaced, the rule you may have tuned is kept.

The complete pack, with its setup notice, is in packs/shelly-plug. Everything the format accepts is in the reference.