​Expressions

Expressions & Context Variables

Overview

Kestra's expressions combine the Pebble templating engine with the execution context to dynamically render flow properties. This page lists available expressions and explains how to use them in your flows.

Using Expressions

To dynamically set values in your flows, wrap an expression in curly braces, e.g. {{ your_expression }}.

Flows, tasks, executions, triggers, and schedules come with built-in expressions. For example:

• {{ flow.id }} gives the flow's identifier within an execution
• {{ inputs.myinput }} retrieves an input value passed to the execution
• {{ outputs.mytask.myoutput }} fetches a task's output.

To debug expressions, use the Debug Outputs console as demonstrated in the video below:

Flow and Execution Expressions

Flow and execution expressions let you use the execution context to set task properties. For example, you can reference {{ execution.startDate }} to include the execution's start date in a file name.

Some expressions, such as flow.id or flow.namespace, access metadata stored in the execution context. Others, such as FILE-type inputs and outputs, pull data from Kestra's internal storage or environment variables.

The execution context includes these variables:

• flow
• execution
• inputs
• outputs
• labels
• tasks
• trigger — available if at least one trigger is defined in the flow
• vars — available if variables are defined in the flow configuration
• namespace — available in EE when Variables are set in the Namespace configuration
• envs — environment variables
• globals — global variables.

Default Execution Context Variables

The following table lists the default execution context variables available in Kestra:

Additional Variables for Schedule Trigger

When the execution is triggered by a Schedule, the following variables are also available:

Additional Variables for Flow Trigger

When the execution is triggered by a Flow, the following variables are also available:

All expressions can be used with the Pebble template syntax {{ expression }}. For example:

id: expressions
namespace: company.team

tasks:
  - id: debug_expressions
    type: io.kestra.plugin.core.debug.Return
    format: |
      taskId: {{ task.id }}
      date: {{ execution.startDate | date("yyyy-MM-dd HH:mm:ss.SSSSSS") }}

Environment Variables

Kestra provides access to environment variables prefixed with KESTRA_ by default, unless configured otherwise in the variables configuration.

To use an environment variable, such as KESTRA_FOO, reference it as {{ envs.foo }}. The variable name is derived by removing the KESTRA_ prefix and converting the remainder to lowercase.

To reference the environment name defined in Kestra configuration, you can use {{kestra.environment.name}}. Similarly, using {{kestra.url}}, you can reference the environment's URL set in your Kestra configuration.

Global Variables

You can define global variables in Kestra's configuration and access them using {{ globals.foo }}.

Flow Variables

To avoid hardcoding values in tasks, you can declare variables at the flow level using the variables property. These variables can be accessed anywhere in the flow with the vars.my_variable syntax. For example:

id: flow_variables
namespace: company.team

variables:
  my_variable: "my_value"

tasks:
  - id: print_variable
    type: io.kestra.plugin.core.debug.Return
    format: "{{ vars.my_variable }}"

Inputs

Flow inputs can be referenced using the inputs.inputName syntax. For example:

id: render_inputs
namespace: company.team

inputs:
  - id: myInput
    type: STRING

tasks:
  - id: myTask
    type: io.kestra.plugin.core.debug.Return
    format: "{{ inputs.myInput }}"

Secrets

You can retrieve secrets in your flow using the secret() function. Secrets are stored in a secure way and can be accessed as follows:

id: use_secret_in_flow
namespace: company.team

tasks:
  - id: myTask
    type: io.kestra.plugin.core.debug.Return
    format: "{{ secret('MY_SECRET') }}"

Secrets are supported in both the open-source version and Enterprise Edition. For additional details, refer to the Secrets documentation.

Namespace Variables (EE)

Namespace variables are key-value pairs defined in YAML configuration. They can be nested and referenced in flows using dot notation, e.g., {{ namespace.myproject.myvariable }}. To define namespace variables:

1. Navigate to Namespaces in the Kestra UI.
2. Select the namespace.
3. Add variables in the Variables tab.

Namespace variables are scoped to the specific namespace and inherited by child namespaces. Reference these variables in your flow using the namespace.your_variable syntax. Example:

id: namespace_variables
namespace: company.team

tasks:
  - id: myTask
    type: io.kestra.plugin.core.debug.Return
    format: "{{ namespace.your_variable }}"

If a namespace variable contains Pebble expressions, such as {{ secret('GITHUB_TOKEN') }}, you need to use the render function to evaluate it. For example, assume the following variable is defined in the Variables tab:

github:
  token: "{{ secret('GITHUB_TOKEN') }}"

To reference github.token in your flow, use "{{ render(namespace.github.token) }}":

id: recursive_namespace_variables_rendering
namespace: company.team

tasks:
  - id: myTask
    type: io.kestra.plugin.core.debug.Return
    format: "{{ render(namespace.github.token) }}"

The render() function is required to parse namespace or flow variables containing Pebble expressions. Without it, the variable is treated as a string, and its expressions are not evaluated.

Outputs

Task outputs can be accessed using {{ outputs.taskId.outputAttribute }}, where:

• taskId is the ID of the task
• outputAttribute is the attribute of the task's output. Each task emits specific output attributes — refer to task documentation for details.

Example of passing data between tasks using outputs:

id: pass_data_between_tasks
namespace: company.team

tasks:
  - id: first
    type: io.kestra.plugin.core.debug.Return
    format: First output value

  - id: second-task
    type: io.kestra.plugin.core.debug.Return
    format: Second output value

  - id: print_both_outputs
    type: io.kestra.plugin.core.log.Log
    message: |
      First: {{ outputs.first.value }}
      Second: {{ outputs['second-task'].value }}

Pebble Templating

Pebble templating provides many ways to dynamically evaluate expressions.

The example below demonstrates parsing Pebble expressions within variables, based on inputs and trigger values. The Null-Coalescing Operator ?? is used to select the first non-null value.

Parsing Complex Variables

The workflow shown below defines two variables:

1. trigger_or_yesterday:
   • Evaluates to trigger.date if the flow runs on a schedule.
   • If no schedule is available, it defaults to yesterday’s date by subtracting one day from execution.startDate.
2. input_or_yesterday:
   • Evaluates to the mydate input if provided.
   • If the input is absent, it defaults to yesterday’s date, calculated using execution.startDate minus one day with the dateAdd function.

id: render_complex_expressions
namespace: company.team

inputs:
  - id: mydate
    type: DATETIME
    required: false

variables:
  trigger_or_yesterday: "{{ trigger.date ?? (execution.startDate | dateAdd(-1, 'DAYS')) }}"
  input_or_yesterday: "{{ inputs.mydate ?? (execution.startDate | dateAdd(-1, 'DAYS')) }}"

tasks:
  - id: yesterday
    type: io.kestra.plugin.core.log.Log
    message: "{{ render(vars.trigger_or_yesterday) }}"

  - id: input_or_yesterday
    type: io.kestra.plugin.core.log.Log
    message: "{{ render(vars.input_or_yesterday) }}"

Render Function and Null-Coalescing

• render Function: the render function is required to evaluate variables containing Pebble expressions. Without it, variables will be treated as strings, and expressions inside them will not be evaluated.
• Null-Coalescing Operator (??): this operator ensures that the first non-null value is selected, providing a fallback mechanism.

Combining the render() function with the Null-Coalescing operator enables dynamic and flexible parsing of complex expressions.

Expression Usage

This section summarizes the main syntax of filters, functions, and control structures available in Pebble templating.

Syntax Reference

Pebble templates use two primary delimiters:

• {{ ... }}: outputs the result of an expression. Expressions can be simple variables or complex calculations.
• {% ... %}: controls the template’s flow, such as with if statements or for loops.

To escape expressions or control structures, use the raw tag. This prevents Pebble from interpreting content within {{ ... }} or {% ... %}.

Dot notation (.) is used to access nested attributes. For attributes with special characters, use square brackets:

{{ foo.bar }} # Accesses 'bar' in 'foo'
{{ foo['foo-bar'] }} # Accesses 'foo-bar' in 'foo'

For lists, access elements by index with square brackets ([]):

{{ foo[0] }} # Accesses the first element in the list 'foo'

Filters

Filters transform values and are applied using the pipe (|) symbol. Filters can be chained:

{{ "Lemons to lemonade." | upper | abbreviate(10) }}
# Output: LEMONS TO ...

Functions

Functions generate new values. They are called with a name followed by parentheses:

{{ max(user.score, highscore) }}
# Outputs the maximum of 'user.score' and 'highscore'

Control Structures

Pebble supports loops and conditionals to control the flow of templates.

For Loop:

{% for article in articles %}
  {{ article.title }}
{% else %}
  "No articles available."
{% endfor %}

If Statement:

{% if category == "news" %}
  {{ news }}
{% elseif category == "sports" %}
  {{ sports }}
{% else %}
  "Select a category"
{% endif %}

Macros

Macros are reusable template snippets, similar to functions:

{% macro input(type, name) %}
  {{ name }} is of type {{ type }}
{% endmacro %}

Usage:

{{ input("text", "example") }}
# Output: example is of type text

Macros only access their local arguments.

Named Arguments

Filters, functions, and macros support named arguments for clarity:

{{ stringDate | date(existingFormat="yyyy-MMMM-d", format="yyyy/MMMM/d") }}

Named arguments can define defaults in macros:

{% macro input(type="text", name, value="") %}
  type: "{{ type }}", name: "{{ name }}", value: "{{ value }}"
{% endmacro %}

{{ input(name="country") }}
# Output: type: "text", name: "country", value: ""

Comments

Add comments using {# ... #}. They do not appear in output:

{# This is a comment #}
{{ "Visible content" }}

In YAML, use # for comments.

Literals

Pebble supports literals for strings, numbers, booleans, and null values:

• "Hello World": Strings use single or double quotes.
• 100 + 10l * 2.5: Numbers include integers, longs, and floats.
• true, false: Boolean values.
• null: Represents no value.

Collections

Create lists and maps directly:

• ["apple", "banana"]: a list of strings.
• {"apple":"red", "banana":"yellow"}: a map of key-value pairs.

Math

Basic mathematical operators are supported:

• +: Addition
• -: Subtraction
• *: Multiplication
• /: Division
• %: Modulus

Logical Operators

Combine expressions using:

• and: True if both are true.
• or: True if either is true.
• not: Negates an expression.

Comparisons

Pebble supports common comparison operators: ==, !=, <, >, <=, >=.

Tests

Use the is operator to test expressions:

{% if 3 is odd %}
  "Odd number"
{% endif %}

Negate tests with is not:

{% if name is not null %}
  "Name exists"
{% endif %}

Conditional (Ternary) Operator

The conditional operator (?) works like Java's ternary operator:

{{ foo ? "yes" : "no" }}

Null-Coalescing Operator

The ?? operator provides a fallback if a variable is null:

{{ foo ?? bar ?? "default" }}

Raises an exception if no variable is defined:

{{ foo ?? bar ?? raise }}

Operator Precedence

Operators are evaluated in the following order:

1. .
2. |
3. %, /, *
4. -, +
5. ==, !=, >, <, >=, <=
6. is, is not
7. and
8. or

Basic Filters

Filters transform variables in expressions, allowing for operations like formatting, string manipulation, and list processing. Filters are applied using the pipe symbol (|) and can be chained together.

To apply a filter, use this syntax:

{{ name | title }}

This example converts name to title case.

Filters that accept arguments use parentheses. For example, to join a list of strings with commas:

{{ list | join(', ') }}

To apply a filter to a block of text, wrap it with the filter tag:

{% filter lower | title %}
  hello world
{% endfilter %}

JSON Filters

JSON filters are specifically designed to manipulate JSON objects, such as API responses.

toJson

The toJson filter converts any object into a JSON string. Examples:

{{ [1, 2, 3] | toJson }} # Outputs: '[1, 2, 3]'
{{ true | toJson }} # Outputs: 'true'
{{ "foo" | toJson }} # Outputs: '"foo"'

toIon

The toIon filter converts any object into an Ion string. Example:

{{ myObject | toIon }}

jq

The jq filter applies a JQ expression to a variable. The result is always an array formatted as JSON. Use the first filter to extract the first (or only) result.

Examples:

{{ [1, 2, 3] | jq('.') }}
# Outputs: '[1, 2, 3]'

{{ [1, 2, 3] | jq('.[0]') | first }}
# Outputs: '1'

Given the context:

{
  "outputs": {
    "task1": {
      "value": 1,
      "text": "awesome1"
    },
    "task2": {
      "value": 2,
      "text": "awesome2"
    }
  }
}

The following expression extracts the value of task1:

{{ outputs | jq('.task1.value') | first }}
# Outputs: '1'

Arguments

• expression: The JQ expression to apply.

Manipulating JSON Payloads

Here is a comprehensive example of JSON manipulation. This flow takes a JSON payload as input and performs multiple transformations:

id: myflow
namespace: company.myteam

inputs:
  - id: payload
    type: JSON
    defaults: |-
      {
        "name": "John Doe",
        "score": {
          "English": 72,
          "Maths": 88,
          "French": 95,
          "Spanish": 85,
          "Science": 91
        },
        "address": {
          "city": "Paris",
          "country": "France"
        },
        "graduation_years": [2020, 2021, 2022, 2023]
      }

tasks:
  - id: print_status
    type: io.kestra.plugin.core.log.Log
    message:
      - "Student name: {{ inputs.payload.name }}" # Extracting a value
      - "Score in languages: {{ inputs.payload.score.English + inputs.payload.score.French + inputs.payload.score.Spanish }}" # Summing numbers
      - "Total subjects: {{ inputs.payload.score | length }}" # Counting keys in a map
      - "Total score: {{ inputs.payload.score | values | jq('reduce .[] as $num (0; .+$num)') | first }}" # Summing all values
      - "Complete address: {{ inputs.payload.address.city }}, {{ inputs.payload.address.country | upper }}" # Concatenation and transformation
      - "Total years for graduation: {{ inputs.payload.graduation_years | length }}" # Counting array elements
      - "Started college in: {{ inputs.payload.graduation_years | first }}" # First element in an array
      - "Completed college in: {{ inputs.payload.graduation_years | last }}" # Last element in an array

Running this flow will log:

Student name: John Doe
Score in languages: 252
Total subjects: 5
Total score: 431
Complete address: Paris, FRANCE
Total years for graduation: 4
Started college in: 2020
Completed college in: 2023

Numeric Filters

Numeric filters are used to format numbers or convert strings to numbers.

abs

The abs filter returns the absolute value of a number.

{{ -7 | abs }}
# output: 7

number

The number filter parses a string into a number. If no type is specified, the type is inferred.

{{ "12.3" | number | className }}
# output: java.lang.Float

{{ "9223372036854775807" | number('BIGDECIMAL') | className }}
# output: java.math.BigDecimal

• type:
  • INT
  • FLOAT
  • LONG
  • DOUBLE
  • BIGDECIMAL
  • BIGINTEGER

numberFormat

The numberFormat filter formats a number using java.text.DecimalFormat.

{{ 3.141592653 | numberFormat("#.##") }}
# output: 3.14

Object Filters

Object filters manipulate collections such as maps, arrays, or strings.

chunk

The chunk filter partitions a list into chunks of the specified size.

{{ [1, 2, 3, 4, 5] | chunk(2) }}
# results in: [[1, 2], [3, 4], [5]]

className

The className filter returns the class name of an object.

{{ "12.3" | number | className }}
# output: java.lang.Float

distinct

The distinct filter deduplicates a list and returns only the unique values.

"{{ ['1', '1', '2', '3'] | distinct }}"
# results in ["1","2","3"]

first

The first filter retrieves the first item of a collection or the first character of a string.

{{ ['apple', 'banana'] | first }}
# output: apple

{{ 'Mitch' | first }}
# output: M

join

The join filter concatenates the items in a collection into a single string, separated by a specified delimiter.

{{ ['apple', 'banana'] | join(', ') }}
# output: apple, banana

keys

The keys filter retrieves the keys from a map or the indices of an array.

{{ {'foo': 'bar', 'baz': 'qux'} | keys }}
# output: ['foo', 'baz']

values

The values filter retrieves the values from a map.

{{ {'foo': 'bar', 'baz': 'qux'} | values }}
# output: ['bar', 'qux']

last

The last filter retrieves the last item of a collection or the last character of a string.

{{ ['apple', 'banana'] | last }}
# output: banana

{{ 'Mitch' | last }}
# output: h

length

The length filter returns the size of a collection or the length of a string.

{{ 'Mitch' | length }}
# output: 5

merge

The merge filter combines two collections (lists or maps).

{{ [1, 2] | merge([3, 4]) }}
# output: [1, 2, 3, 4]

reverse

The reverse filter reverses the order of items in a collection.

{{ ['apple', 'banana'] | reverse }}
# output: ['banana', 'apple']

rsort

The rsort filter sorts a list in reverse order.

{{ [3, 1, 2] | rsort }}
# output: [3, 2, 1]

slice

The slice filter extracts a portion of a collection or string.

{{ ['apple', 'banana', 'cherry'] | slice(1, 2) }}
# output: ['banana']

{{ 'Mitch' | slice(1, 3) }}
# output: it

Arguments:

• fromIndex: starting index (inclusive).
• toIndex: ending index (exclusive).

sort

The sort filter sorts a collection in ascending order.

{{ [3, 1, 2] | sort }}
# output: [1, 2, 3]

split

The split filter divides a string into a list based on a delimiter.

{{ 'apple,banana,cherry' | split(',') }}
# output: ['apple', 'banana', 'cherry']

Arguments:

• delimiter: the string to split on.
• limit: limits the number of splits:
  • Positive: limits the array size, with the last entry containing the remaining content.
  • Zero or negative: no limit on splits.

{{ 'apple,banana,cherry,grape' | split(',', 2) }}
# output: ['apple', 'banana,cherry,grape']

String Filters

String filters manipulate textual data, enabling operations like transformation, encoding, or formatting.

abbreviate

The abbreviate filter shortens a string using an ellipsis. The length includes the ellipsis.

{{ "this is a long sentence." | abbreviate(7) }}
# output: this...

Arguments:

• length: the maximum length of the output.

base64decode

The base64decode filter decodes a base64-encoded string into UTF-8.

{{ "dGVzdA==" | base64decode }}
# output: test

Throws an exception for invalid base64 strings.

base64encode

The base64encode filter encodes a string to base64.

{{ "test" | base64encode }}
# output: dGVzdA==

capitalize

The capitalize filter capitalizes the first letter of a string.

{{ "article title" | capitalize }}
# output: Article title

title

The title filter capitalizes the first letter of each word.

{{ "article title" | title }}
# output: Article Title

default

The default filter provides a fallback value for empty variables.

{{ user.phoneNumber | default("No phone number") }}
# output: No phone number (if user.phoneNumber is empty)

Suppresses exceptions if the attribute is missing.

escapeChar

The escapeChar filter escapes special characters in a string.

{{ "Can't be here" | escapeChar('single') }}
# output: Can\'t be here

Arguments:

• type: escape type (single, double, or shell).

lower

The lower filter converts a string to lowercase.

{{ "LOUD TEXT" | lower }}
# output: loud text

replace

The replace filter replaces substrings in a string with specified values.

{{ "I like %this% and %that%." | replace({'%this%': foo, '%that%': "bar"}) }}
# output: I like foo and bar

Arguments:

• replace_pairs: a map of search-replace pairs.
• regexp: enables regex-based replacements.

sha256

The sha256 filter generates a SHA-256 hash of a string.

{{ "test" | sha256 }}
# output: 9f86d081884c7d659a2feaa0c55ad015a3bf4f1b2b0b822cd15d6c15b0f00a08

startsWith

The startsWith filter checks if a string starts with a given prefix.

{{ "hello world" | startsWith("hello") }}
# output: true

slugify

The slugify filter converts a string to a URL-friendly format.

{{ "Hello World!" | slugify }}
# output: hello-world

substringAfter

The substringAfter filter extracts the substring after the first occurrence of a separator.

{{ "a.b.c" | substringAfter(".") }}
# output: b.c

substringAfterLast

The substringAfterLast filter extracts the substring after the last occurrence of a separator.

{{ "a.b.c" | substringAfterLast(".") }}
# output: c

substringBefore

The substringBefore filter extracts the substring before the first occurrence of a separator.

{{ "a.b.c" | substringBefore(".") }}
# output: a

substringBeforeLast

The substringBeforeLast filter extracts the substring before the last occurrence of a separator.

{{ "a.b.c" | substringBeforeLast(".") }}
# output: a.b

trim

The trim filter removes whitespace from the start and end of a string.

{{ "   padded text   " | trim }}
# output: padded text

upper

The upper filter converts a string to uppercase.

{{ "quiet sentence" | upper }}
# output: QUIET SENTENCE

urldecode

The urldecode filter decodes a URL-encoded string.

{{ "The+string+%C3%BC%40foo-bar" | urldecode }}
# output: The string ü@foo-bar

urlencode

The urlencode filter encodes a string for URLs.

{{ "The string ü@foo-bar" | urlencode }}
# output: The+string+%C3%BC%40foo-bar

string

The string filter casts an object to string.

{{ 123 | string }}
# output: "123"

Temporal Filters

Temporal filters are used for formatting, manipulating, and converting dates and timestamps.

date

The date filter formats a date object or string into a specified format. It supports java.util.Date, java.time constructs like OffsetDateTime, and epoch timestamps in milliseconds.

{{ user.birthday | date("yyyy-MM-dd") }}
# output: 2001-07-24

To format a string-based date, provide the desired output format and the existing format of the string:

{{ "July 24, 2001" | date("yyyy-MM-dd", existingFormat="MMMM dd, yyyy") }}
# output: 2001-07-24

Time Zones

Specify a custom time zone using the timeZone argument:

{{ now() | date("yyyy-MM-dd'T'HH:mm:ssX", timeZone="UTC") }}

Arguments:

• format: the desired output format.
• existingFormat: the input format (if parsing a string).
• timeZone: the time zone for formatting.
• locale: the locale for formatting.

Supported Date Formats

• Standard Java formats: DateTimeFormatter
• Presets: iso, sql, iso_date_time, iso_zoned_date_time, etc.

dateAdd

The dateAdd filter adds or subtracts a specified amount of time to/from a date.

{{ now() | dateAdd(-1, 'DAYS') }}
# output: 2024-07-08T06:17:01.174686Z

Arguments:

• amount: an integer specifying the time to add/subtract.
• unit: the time unit (e.g., DAYS, HOURS, YEARS).
• Additional arguments: same as the date filter.

timestamp

The timestamp filter converts a date to a Unix timestamp in seconds.

{{ now() | timestamp(timeZone="Europe/Paris") }}
# output: 1720505821

Arguments:

• existingFormat: the input format (if parsing a string).
• timeZone: the time zone for conversion.

timestampMicro

The timestampMicro filter converts a date to a Unix timestamp in microseconds.

{{ now() | timestampMicro(timeZone="Asia/Kolkata") }}
# output: 1720505821000180275

Arguments:

• Same as timestamp.

timestampNano

The timestampNano filter converts a date to a Unix timestamp in nanoseconds.

{{ now() | timestampNano(timeZone="Asia/Kolkata") }}
# output: 1720505821182413000

Arguments:

• Same as timestamp.

Example with Temporal Filters

Here’s an example flow showcasing the use of temporal filters:

id: temporal-dates
namespace: company.myteam

tasks:
  - id: print_status
    type: io.kestra.plugin.core.log.Log
    message:
      - "Present timestamp: {{ now() }}"
      - "Formatted timestamp: {{ now() | date('yyyy-MM-dd') }}"
      - "Previous day: {{ now() | dateAdd(-1, 'DAYS') }}"
      - "Next day: {{ now() | dateAdd(1, 'DAYS') }}"
      - "Timezone (seconds): {{ now() | timestamp(timeZone='Asia/Kolkata') }}"
      - "Timezone (microseconds): {{ now() | timestampMicro(timeZone='Asia/Kolkata') }}"
      - "Timezone (nanoseconds): {{ now() | timestampNano(timeZone='Asia/Kolkata') }}"

Running this flow will log the following:

Present timestamp: 2024-07-09T06:17:01.171193Z
Formatted timestamp: 2024-07-09
Previous day: 2024-07-08T06:17:01.174686Z
Next day: 2024-07-10T06:17:01.176138Z
Timezone (seconds): 1720505821
Timezone (microseconds): 1720505821000180275
Timezone (nanoseconds): 1720505821182413000

YAML Filters

YAML filters allow you to parse and manipulate YAML strings, converting them into objects that can be processed further.

yaml

The yaml filter, introduced in Kestra 0.16.0, parses a YAML string into an object. This is especially useful when working with templated tasks, such as the TemplatedTask.

Example:

{{ "foo: bar" | yaml }}

Example: Using the yaml filter in a templated task

id: yaml_filter_example
namespace: company.team

tasks:
  - id: yaml_filter
    type: io.kestra.plugin.core.log.Log
    message: |
      {{ "foo: bar" | yaml }}
      {{ {"key": "value"} | yaml }}

indent

The indent filter adds indentation to strings, applying the specified number of spaces before each line (except the first).

Arguments:

• amount: number of spaces to add.
• prefix: the string used for indentation (default is " ").

Example:

{{ "key: value" | indent(2) }}
# output:
  key: value

nindent

The nindent filter adds a newline before the input and then indents all lines.

Arguments:

• amount: number of spaces for indentation.
• prefix: the string used for indentation (default is " ").

Example:

{{ "key: value" | nindent(2) }}
# output:
  key: value

Example with indent and nindent

id: templated_task_example
namespace: company.team

labels:
  example: test

variables:
  yaml_data: |
    key1: value1
    key2: value2

tasks:
  - id: yaml_with_indent
    type: io.kestra.plugin.core.templating.TemplatedTask
    spec: |
      id: example-task
      type: io.kestra.plugin.core.log.Log
      message: |
        Metadata:
        {{ labels | yaml | indent(4) }}

        Variables:
        {{ variables.yaml_data | yaml | nindent(4) }}

The above example generates a task with indented YAML content for both labels and variables.

Here is an explanation of the filters used:

• Using yaml: converts the YAML string into an object.
• Using indent(4): adds four spaces before each line.
• Using nindent(4): adds a newline and then indents with four spaces.

Functions

Functions in Kestra allow you to dynamically generate or manipulate content. They are invoked by their name followed by parentheses () and can accept arguments.

errorLogs

The errorLogs() function retrieves a list of error logs from the failed task run. This is useful when sending alerts on failure. When using this function e.g. in a Slack alert message, you'll have a context about why the execution failed.

id: error_logs_demo
namespace: company.team

tasks:
  - id: fail
    type: io.kestra.plugin.core.execution.Fail
    errorMessage: Something went wrong, make sure to fix it asap ⚠️

errors:
  - id: alert
    type: io.kestra.plugin.core.log.Log
    message: list of error logs — {{ errorLogs() }}>

block

The block function renders the contents of a block multiple times. It is distinct from the block tag used to declare blocks.

Example:

{% block "post" %}content{% endblock %}

{{ block("post") }}

Output:

content
content

currentEachOutput

The currentEachOutput function simplifies retrieving outputs of sibling tasks within an EachSequential task.

Example:

tasks:
  - id: each
    type: io.kestra.plugin.core.flow.EachSequential
    tasks:
      - id: first
        type: io.kestra.plugin.core.debug.Return
        format: "{{task.id}}"
      - id: second
        type: io.kestra.plugin.core.debug.Return
        format: "{{ currentEachOutput(outputs.first).value }}"
    value: ["value 1", "value 2", "value 3"]

This eliminates the need for manual handling of taskrun.value or parents.

fromJson

The fromJson function parses a JSON string into an object, enabling property access.

Examples:

{{ fromJson('[1, 2, 3]')[0] }}
# output: 1

{{ fromJson('{"foo": [666, 1, 2]}').foo[0] }}
# output: 666

fromIon

The fromIon function parses a ION string into an object, enabling property access.

Example:

{{ fromIon(read(someItem)).someField }}

yaml

The yaml function parses a YAML string into an object.

Example:

{{ yaml('foo: [666, 1, 2]').foo[0] }}
# output: 666

max

The max function returns the largest of its arguments.

Example:

{{ max(20, 80, user.age) }}
# output: the largest value

min

The min function returns the smallest of its arguments.

Example:

{{ min(20, 80, user.age) }}
# output: the smallest value

now

The now function generates the current datetime. Formatting options are the same as the date filter.

Example:

{{ now() }}
{{ now(timeZone="Europe/Paris") }}

parent

The parent function renders the parent block's content within a child block.

Example:

Parent template (parent.peb):

{% block "content" %}parent content{% endblock %}

Child template (child.peb):

{% extends "parent.peb" %}

{% block "content" %}
child content
{{ parent() }}
{% endblock %}

Output:

child content
parent content

range

The range function generates a list of numbers.

Examples:

{% for i in range(0, 3) %}
    {{ i }},
{% endfor %}
# output: 0, 1, 2, 3

{% for i in range(0, 6, 2) %}
    {{ i }},
{% endfor %}
# output: 0, 2, 4, 6

printContext

The printContext function is used for debugging by printing all defined variables.

Example:

{{ printContext() }}

Output:

{"outputs": {...}, "execution": {...}, ...}

read

The read function retrieves the contents of a file from internal storage or namespace files.

Examples:

{{ read('subdir/file.txt') }}
{{ read(outputs.someTask.uri) }}

render

The render function enables recursive rendering of expressions. By default, Kestra only renders expressions once.

Example:

{{ render("{{ trigger.date ?? execution.startDate | date('yyyy-MM-dd') }}") }}

Arguments:

• recursive: defaults to true. Set to false for one-time rendering.

renderOnce

Equivalent to render(expression, recursive=false). It simplifies rendering without recursion.

secret

The secret function retrieves secrets stored in Kestra's secret backend.

Example:

tasks:
  - id: github_secret
    type: io.kestra.plugin.core.log.Log
    message: "{{ secret('GITHUB_ACCESS_TOKEN') }}"

randomInt

The randomInt function generates a random integer from a specified range.

Example with a range between 1 and 10:

tasks:
  - id: random
    type: io.kestra.plugin.core.log.Log
    message: "{{ randomInt(1, 10) }}"

uuid

The uuid function generates a UUID in the Kestra format (i.e., a UUID encoded in Url62).

Example:

tasks:
  - id: uuid
    type: io.kestra.plugin.core.log.Log
    message: "Generated UUID: {{ uuid() }}"
    # Output: Generated UUID: d815cb05-ac71-429d-8e73-f7c92f5429c4

randomPort

The randomPort function generate a random available port.

Example:

tasks:
  - id: port
    type: io.kestra.plugin.core.log.Log
    message: "Generated Port: {{ randomPort() }}"

fileSize

The fileSize function returns the size of the file present at the given URI.

Example:

tasks:
  - id: download
    type: io.kestra.plugin.core.http.Download
    uri: https://huggingface.co/datasets/kestra/datasets/raw/main/csv/orders.csv
  
  - id: fileSize
    type: io.kestra.plugin.core.log.Log
    message: "The file size is {{ fileSize(output.download.uri) }}"

fileExists

The fileExists function returns true if the file is present at the given URI.

tasks:
  - id: download
    type: io.kestra.plugin.core.http.Download
    uri: https://huggingface.co/datasets/kestra/datasets/raw/main/csv/orders.csv

  - id: fileExists
    type: io.kestra.plugin.core.log.Log
    message: "The file exists: {{ fileExists(output.download.uri) }}"

fileEmpty

The fileEmpty function returns true if the file present at the given URI is empty.

tasks:
  - id: download
    type: io.kestra.plugin.core.http.Download
    uri: https://huggingface.co/datasets/kestra/datasets/raw/main/csv/orders.csv

  - id: fileEmpty
    type: io.kestra.plugin.core.log.Log
    message: "Is the file empty? {{ fileEmpty(output.download.uri) }}"

Example with Functions

id: function_example
namespace: company.team

tasks:
  - id: max_example
    type: io.kestra.plugin.core.log.Log
    message: "Maximum value: {{ max(5, 10, 15) }}"

  - id: render_example
    type: io.kestra.plugin.core.log.Log
    message: "{{ render('{{ trigger.date ?? execution.startDate | date("yyyy-MM-dd") }}') }}"

  - id: secret_example
    type: io.kestra.plugin.core.log.Log
    message: "{{ secret('API_KEY') }}"
    allowFailure: true

Operators

Operators enable logical, arithmetic, and comparison operations within templated expressions. They are essential for dynamic content manipulation.

Comparison Operators

Supported comparison operators: ==, !=, <, >, <=, >=.

• ==: Uses Java.util.Objects.equals(a, b) for null-safe comparisons. Alias: equals.

Example:

{% if user.name equals "Mitchell" %}
    ...
{% endif %}

concat

The ~ operator concatenates two or more strings.

Example:

{{ "apple" ~ "pear" ~ "banana" }}
# results in: 'applepearbanana'

contains

The contains operator checks if an item exists within a collection, map, or array.

Examples:

{% if ["apple", "pear", "banana"] contains "apple" %}
    ...
{% endif %}

For maps, it checks for an existing key:

{% if {"apple":"red", "banana":"yellow"} contains "banana" %}
    ...
{% endif %}

To check multiple items:

{% if ["apple", "pear", "banana", "peach"] contains ["apple", "peach"] %}
    ...
{% endif %}

is

The is operator tests variables, returning a boolean.

Examples:

{% if 2 is even %}
    ...
{% endif %}

Negation with not:

{% if 3 is not even %}
    ...
{% endif %}

logic

Combine boolean expressions using and and or. Use not for negation.

Examples:

{% if 2 is even and 3 is odd %}
    ...
{% endif %}

{% if 3 is not even %}
    ...
{% endif %}

Group expressions with parentheses for precedence:

{% if (3 is not even) and (2 is odd or 3 is even) %}
    ...
{% endif %}

math

Perform arithmetic operations with standard math operators. Follow the order of operations.

Example:

{{ 2 + 2 / (10 % 3) * (8 - 1) }}

Supported operators:

• +: Addition
• -: Subtraction
• /: Division (returns a float)
• %: Modulus
• *: Multiplication

not

Use not with is to negate a test.

Example:

{% if 3 is not even %}
    ...
{% endif %}

null-coalescing

The null-coalescing operator (??) returns the first defined, non-null value. Use ??? to return the right-hand side only if the left-hand side is undefined.

Examples:

{% set baz = "baz" %}
{{ foo ?? bar ?? baz }}
# results in: 'baz'

{{ foo ?? bar ?? raise }}
# raises an exception if all variables are undefined

For details, see the Handling null and undefined values guide.

ternary operator

The ternary operator (? :) evaluates conditions succinctly.

Example:

{{ foo == null ? bar : baz }}

Tag

Tags in Pebble control the template's flow and logic. They are enclosed in {% %}.

block

The block tag defines reusable template blocks.

Example:

{% block header %}
    Introduction
{% endblock %}

To reuse a block, use the block function:

{{ block("header") }}

filter

The filter tag applies a filter to a block of content.

Example:

{% filter upper %}
    hello
{% endfilter %}

Output:

HELLO

Filters can be chained:

{% filter upper | title %}
    hello
{% endfilter %}

Output:

Hello

for

The for tag iterates over arrays, maps, or any java.lang.Iterable.

Example:

{% for user in users %}
    {{ user.name }} lives in {{ user.city }}.
{% endfor %}

Special variables available within a loop:

• loop.index: zero-based index
• loop.length: total size of the iterable
• loop.first: true if it's the first iteration
• loop.last: true if it's the last iteration
• loop.revindex: iterations remaining until the end

{% for user in users %}
    {{ loop.index }}: {{ user.id }}
{% endfor %}

To handle empty collections, use the else tag:

{% for user in users %}
    {{ user.name }}
{% else %}
    No users found.
{% endfor %}

For maps:

{% for entry in map %}
    {{ entry.key }}: {{ entry.value }}
{% endfor %}

if

The if tag evaluates conditional logic.

Example:

{% if users is empty %}
    No users available.
{% elseif users.length == 1 %}
    One user found.
{% else %}
    Multiple users found.
{% endif %}

if expressions can include:

• boolean values
• is operator (e.g., is empty, is not empty)

macro

The macro tag defines reusable blocks of content.

Example:

{% macro input(type="text", name, value) %}
    <input type="{{ type }}" name="{{ name }}" value="{{ value }}">
{% endmacro %}

{{ input(name="username") }}

Output:

<input type="text" name="username" value="">

Passing global context:

{% set foo = 'bar' %}

{{ test(_context) }}
{% macro test(_context) %}
    {{ _context.foo }}
{% endmacro %}

Output:

bar

raw

The raw tag prevents Pebble from parsing its content.

Example:

{% raw %}
    {{ user.name }}
{% endraw %}

Output:

{{ user.name }}

set

The set tag defines a variable in the template context.

Example:

{% set header = "Welcome Page" %}

{{ header }}

Output:

Welcome Page

Test

Tests in Pebble are used to perform logical checks, such as determining if a variable is defined, empty, or of a specific type.

defined

Checks if a variable is defined.

{% if missing is not defined %}
    ...
{% endif %}

empty

Checks if a variable is empty. A variable is considered empty if it is:

• null
• an empty string
• an empty collection
• an empty map

{% if user.email is empty %}
    ...
{% endif %}

even

Checks if an integer is even.

{% if 2 is even %}
    ...
{% endif %}

iterable

Checks if a variable implements java.lang.Iterable.

{% if users is iterable %}
    {% for user in users %}
        ...
    {% endfor %}
{% endif %}

json

Checks if a variable is a valid JSON string.

{% if '{"test": 1}' is json %}
    ...
{% endif %}

map

Checks if a variable is an instance of a map.

{% if {"apple":"red", "banana":"yellow"} is map %}
    ...
{% endif %}

null

Checks if a variable is null.

{% if user.email is null %}
    ...
{% endif %}

odd

Checks if an integer is odd.

{% if 3 is odd %}
    ...
{% endif %}

Expressions FAQ