Evaluate Template

Evaluate Jinja2 templates using Home Assistant's template engine.

This tool allows testing and debugging of Jinja2 template expressions that are commonly used in Home Assistant automations, scripts, and configurations. It provides real-time evaluation with access to all Home Assistant states, functions, and template variables.

When NOT to use this for automation/script logic: Templates have legitimate uses (notification bodies, dynamic data.* values, debugging existing templates), but condition: / trigger: positions and action service names are better expressed as native HA constructs: native constructs are schema-validated at config load and surface structural errors loudly, whereas equivalent template logic only errors at runtime — and a template that renders a non-truthy value is silently treated as false. Prefer:

• condition: numeric_state over {{ states('x') | float > N }}

• condition: state over {{ is_state(...) }}

• condition: time / condition: sun over now().hour / is_state('sun.sun', ...)

• Native for: field on state/numeric_state triggers and state conditions over {{ now() - X.last_changed > timedelta(...) }} duration math

• choose action over templated service: / action: strings See ha_get_skill_guide (best-practices skill) for the full anti-pattern list.

When to use (reach for this tool, don't compute it yourself): Any one-shot question whose answer is DERIVED from current HA state — an average/sum/min/max across sensors, a count of entities matching a condition, a boolean comparison, or a rendered message with live values. One render call beats fetching N states and doing the math yourself, and it is the canonical way to test a template before embedding it. This is for one-shot answers and template testing only — NOT for putting templates into automation logic; for condition: / trigger: positions native constructs win.

• "average temperature across the bedroom sensors" -> {{ ([states('sensor.a'), states('sensor.b')] | map('float', 0) | sum) / 2 }}

• "how many lights are on" -> {{ states.light | selectattr('state', 'eq', 'on') | list | count }} NOT for a plain single-entity value ("what's the state of X") — that is ha_get_state / ha_search; rendering {{ states('X') }} there is over-use.

Parameters:

• template: The Jinja2 template string to evaluate

• timeout: Maximum evaluation time in seconds (default: 3)

• report_errors: Whether to return detailed error information (default: True)

Common Template Functions:

State Access:

{{ states('sensor.temperature') }}              # Get entity state value
{{ states.sensor.temperature.state }}           # Alternative syntax
{{ state_attr('light.bedroom', 'brightness') }} # Get entity attribute
{{ is_state('light.living_room', 'on') }}       # Check if entity has specific state

Numeric Operations:

{{ states('sensor.temperature') | float(0) }}   # Convert to float with default
{{ states('sensor.humidity') | int(0) }}        # Convert to integer with default
{{ (states('sensor.temp') | float(0) + 5) | round(1) }} # Math operations

Time and Date:

{{ now() }}                                     # Current datetime
{{ now().strftime('%H:%M:%S') }}               # Format current time
{{ as_timestamp(now()) }}                      # Convert to Unix timestamp
{{ now().hour }}                               # Current hour (0-23)
{{ now().weekday() }}                          # Day of week (0=Monday)

Conditional Logic (for display strings — not for condition: positions):

{{ 'Day' if now().hour < 18 else 'Night' }}    # Ternary operator
{% if is_state('alarm_control_panel.home', 'armed_away') %}
  Alarm is armed
{% else %}
  Alarm is disarmed
{% endif %}

Lists and Loops:

{% for entity in states.light %}
  {{ entity.entity_id }}: {{ entity.state }}
{% endfor %}

{{ states.light | selectattr('state', 'eq', 'on') | list | count }} # Count on lights

String Operations:

{{ states('sensor.weather') | title }}         # Title case
{{ 'Hello ' + states('input_text.name') }}     # String concatenation
{{ states('sensor.data') | regex_replace('pattern', 'replacement') }}

Device and Area Functions:

{{ device_entities('device_id_here') }}        # Get entities for device
{{ area_entities('living_room') }}             # Get entities in area
{{ device_id('light.bedroom') }}               # Get device ID for entity

Common Use Cases (legitimate template positions):

Dynamic Service Data:

# Dynamic brightness based on time
{{ 255 if now().hour < 22 else 50 }}

# Message with current values
"Temperature is {{ states('sensor.temp') }}°C, humidity {{ states('sensor.humidity') }}%"

Examples:

Test basic state access:

ha_eval_template("{{ states('light.living_room') }}")

Test a string expression (e.g. for a notification body):

ha_eval_template("{{ 'Day' if now().hour < 18 else 'Night' }}")

Test mathematical operations:

ha_eval_template("{{ (states('sensor.temperature') | float(0) + 5) | round(1) }}")

Test entity counting:

ha_eval_template("{{ states.light | selectattr('state', 'eq', 'on') | list | count }}")

IMPORTANT NOTES:

• Templates have access to all current Home Assistant states and attributes

• Use this tool to test templates before using them in automations or scripts

• Template evaluation respects Home Assistant's security model and timeouts

• Complex templates may affect Home Assistant performance - keep them efficient

• Use default values (e.g., | float(0)) to handle missing or invalid states

For template documentation: https://www.home-assistant.io/docs/configuration/templating/