Liquid filters

Filters transform values inside Liquid expressions. Pipe a value through a filter with |. The workflow engine provides the standard LiquidJS filter set plus two custom additions: json_parse and entries.

This page is the full categorized catalog. For the mental model and syntax, refer to Templating engine.

Custom filters (workflow-specific)

`json_parse`

Parses a JSON string into a structured value. The counterpart of the standard json filter, which serializes a value to a JSON string.

# HTTP response body is a JSON string; parse it to access fields
config: "{{ steps.http.output.body | json_parse }}"
host:   "{{ steps.http.output.body | json_parse | map: 'host' | first }}"

Use when you have a string that happens to be JSON and you need to index into it.

`entries`

Converts an object into an array of [key, value] pairs so you can iterate an object's properties.

message: |
  {% for kv in steps.config.output | entries %}
    {{ kv[0] }}: {{ kv[1] }}
  {% endfor %}

Use when you don't know the keys in advance but you want to iterate them all.

Note

to_json doesn't exist. For serialization, use json; for parsing, use json_parse.

Strings

upcase, downcase, capitalize, strip, lstrip, rstrip, truncate, truncatewords, replace, replace_first, replace_last, remove, remove_first, remove_last, prepend, append, slice, strip_html, strip_newlines, slugify, number_of_words, escape, escape_once.

Worked examples:

# Uppercase
title: "{{ event.rule.name | upcase }}"

# Truncate with ellipsis
preview: "{{ steps.summary.output.text | truncate: 140 }}"

# Remove a substring
cleaned: "{{ msg | remove: 'REDACTED: ' }}"

# Slug for a URL
slug: "{{ event.rule.name | slugify }}"

# Replace and capitalize
friendly: "{{ raw | replace: '_', ' ' | capitalize }}"

Arrays

join, split, first, last, size, map, compact, sort, sort_natural, uniq, reverse, concat, push, pop, shift, unshift, where, where_exp, find, find_exp, has, has_exp, reject, reject_exp, group_by, group_by_exp, array_to_sentence_string.

Worked examples:

# Extract one field from each element
ids: "${{ event.alerts | map: '_id' }}"

# Filter by a simple equality
critical: "${{ event.alerts | where: 'kibana.alert.risk_score', 90 }}"

# Filter with an expression (where_exp) for OR / comparison / multi-field
high_severity: "${{ event.alerts | where_exp: 'a', 'a.severity == \"high\" or a.severity == \"critical\"' }}"

# Count
count: "{{ event.alerts | size }}"

# Join into a human-readable list
hosts: "{{ event.alerts | map: 'host.name' | uniq | join: ', ' }}"

# Group by a key
by_host: "${{ event.alerts | group_by: 'host.name' }}"

Tip

Use where: <field>, <value> for simple equality. Use where_exp: <name>, '<expr>' for anything more complex (OR conditions, comparisons, multi-field predicates).

Numbers

abs, ceil, floor, round, plus, minus, times, divided_by, modulo, at_least, at_most.

Worked examples:

# Percent with rounding
pct: "{{ error_rate | times: 100 | round: 2 }}%"

# Clamp to a ceiling
capped: "{{ count | at_most: 1000 }}"

# Arithmetic
next: "{{ variables.counter | plus: 1 }}"

Dates

date, date_to_string, date_to_long_string, date_to_rfc822, date_to_xmlschema.

Worked examples:

# Custom format (strftime)
today: "{{ now | date: '%Y-%m-%d' }}"

# Timezone-aware output
at: "{{ execution.startedAt | date: '%Y-%m-%d %H:%M:%S %Z' }}"

# ISO 8601 (XML schema)
iso: "{{ now | date_to_xmlschema }}"

Encoding and JSON

json, json_parse (custom), base64_encode, base64_decode, url_encode, url_decode, cgi_escape, uri_escape, xml_escape.

Worked examples:

# Serialize to a JSON string (for logging or string bodies)
payload: "{{ event.alerts[0] | json }}"

# Parse a JSON string (the counterpart)
parsed: "{{ steps.http.output.body | json_parse }}"

# URL-encode a query parameter
search_url: "https://example.com/search?q={{ inputs.term | url_encode }}"

# Base64 for basic auth
basic: "{{ inputs.user | append: ':' | append: inputs.pass | base64_encode }}"

Objects

entries (custom), default.

Worked examples:

# Fallback for missing values
name: "{{ event.alerts[0].host.name | default: 'unknown' }}"

# Iterate object keys
message: |
  {% for kv in steps.config.output | entries %}
    - {{ kv[0] }} = {{ kv[1] }}
  {% endfor %}

Chain filters

Filters compose. The output of one feeds the next:

top_3_hosts: "{{ event.alerts | map: 'host.name' | uniq | slice: 0, 3 | join: ', ' }}"

Reads left to right: map each alert to its host name, remove duplicates, take the first three, join with commas.

Templating engine: The mental model and the {{ }} vs. ${{ }} distinction.
Context variables: The data you can filter.
Data steps: For transformations too big for filters (filter, group, parse, extract).
LiquidJS documentation: Upstream filter semantics and corner cases.