Templating and Functions

Replay uses Handlebars-style {{ var }} syntax for variable interpolation, plus 45 built-in functions for data transformation.

Variable Interpolation

Any string field in a step can reference state variables:

- name: dynamic-request
  type: http
  request:
    url: /users/{{ user_id }}
    headers:
      Authorization: Bearer {{ token }}
    body:
      name: "{{ user_name }}"
      email: "{{ user_email }}"

Variables are resolved at execution time from the current state bag.

Nested Access

Access nested fields with dot notation:

name: "{{ config.http.base_url }}"
message: "Hello {{ user.profile.first_name }}"

Environment Variables

Environment variables are loaded into the global scope at startup. Access them directly:

config:
  postgres:
    dsn: postgres://{{ POSTGRES_USER }}:{{ POSTGRES_PASSWORD }}@localhost:5433/mydb

Built-in Functions

String Functions

Function	Description	Example	Result
`upper`	Convert to uppercase	`{{upper "hello"}}`	`HELLO`
`lower`	Convert to lowercase	`{{lower "HELLO"}}`	`hello`
`upperFirst`	Capitalize first letter	`{{upperFirst "hello"}}`	`Hello`
`lowerFirst`	Lowercase first letter	`{{lowerFirst "Hello"}}`	`hello`
`trim`	Trim whitespace	`{{trim " hi "}}`	`hi`
`replace`	Replace all occurrences	`{{replace "a-b-c" "-" "."}}`	`a.b.c`
`contains`	Check substring	`{{contains "hello" "ell"}}`	`true`
`startsWith`	Check prefix	`{{startsWith "hello" "he"}}`	`true`
`endsWith`	Check suffix	`{{endsWith "hello" "lo"}}`	`true`
`split`	Split string	`{{split "a,b,c" ","}}`	`["a","b","c"]`
`join`	Join array	`{{join (split "a,b" ",") "-"}}`	`a-b`
`truncate`	Truncate with ellipsis	`{{truncate "hello world" 8}}`	`hello...`
`padLeft`	Pad left	`{{padLeft "42" 5 "0"}}`	`00042`
`padRight`	Pad right	`{{padRight "42" 5 "."}}`	`42...`
`repeat`	Repeat string	`{{repeat "ab" 3}}`	`ababab`
`regexMatch`	Regex test	`{{regexMatch "^\\d+$" "123"}}`	`true`
`regexFind`	Regex find first	`{{regexFind "\\d+" "abc123def"}}`	`123`

Math Functions

Function	Description	Example	Result
`add`	Addition	`{{add 5 3}}`	`8`
`sub`	Subtraction	`{{sub 10 4}}`	`6`
`mul`	Multiplication	`{{mul 3 4}}`	`12`
`div`	Division	`{{div 10 3}}`	`3.333`
`mod`	Modulo	`{{mod 10 3}}`	`1`
`min`	Minimum	`{{min 5 3}}`	`3`
`max`	Maximum	`{{max 5 3}}`	`5`
`round`	Round	`{{round 3.7}}`	`4`
`abs`	Absolute value	`{{abs -5}}`	`5`
`ceil`	Ceiling	`{{ceil 3.2}}`	`4`
`floor`	Floor	`{{floor 3.8}}`	`3`

Date Functions

Function	Description	Example	Result
`now`	Current UTC time (RFC3339)	`{{now}}`	`2026-06-03T12:00:00Z`
`nowUnix`	Current Unix timestamp	`{{nowUnix}}`	`1759507200`
`addMinutes`	Add minutes	`{{addMinutes "2026-01-01T00:00:00Z" 30}}`	`2026-01-01T00:30:00Z`
`addHours`	Add hours	`{{addHours "2026-01-01T00:00:00Z" 2}}`	`2026-01-01T02:00:00Z`
`addDays`	Add days	`{{addDays "2026-01-01T00:00:00Z" 7}}`	`2026-01-08T00:00:00Z`
`formatDate`	Format date	`{{formatDate "2026-01-01T00:00:00Z" "2006-01-02"}}`	`2026-01-01`
`parseDate`	Parse date string	`{{parseDate "2026-01-01" "2006-01-02"}}`	`2026-01-01T00:00:00Z`
`dateSub`	Date difference (seconds)	`{{dateSub "2026-01-02T00:00:00Z" "2026-01-01T00:00:00Z"}}`	`86400`

JSON Functions

Function	Description
`jsonStringify`	Convert value to JSON string
`jsonParse`	Parse JSON string to value
`jsonPick`	Extract nested value from object by path
`jsonKeys`	Get object keys
`jsonValues`	Get object values
`object`	Build object from key-value pairs
`merge`	Merge two objects

Type Conversion Functions

Function	Description
`toInt`	Convert to integer
`toFloat`	Convert to float
`toString`	Convert to string
`len`	Length of string, array, or object

Combining Functions

Functions can be nested:

message: "{{ upper (trim user_name) }}"
message: "{{ add (toInt count) 1 }}"
message: "{{ join (split tags ",") ", " }}"

What’s Next?

Deep-dive into working with JSON — extraction and assertions
Integrate with CI/CD pipelines

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Contributing

Templating and Functions

Templating and Functions

Variable Interpolation

Nested Access

Environment Variables

Built-in Functions

String Functions

Math Functions

Date Functions

JSON Functions

Type Conversion Functions

Combining Functions

What’s Next?

​Templating and Functions

​Variable Interpolation

​Nested Access

​Environment Variables

​Built-in Functions

​String Functions

​Math Functions

​Date Functions

​JSON Functions

​Type Conversion Functions

​Combining Functions

​What’s Next?

Templating and Functions

Variable Interpolation

Nested Access

Environment Variables

Built-in Functions

String Functions

Math Functions

Date Functions

JSON Functions

Type Conversion Functions

Combining Functions

What’s Next?