Template Expression

Template expressions let you generate text dynamically from runtime data.

Syntax Overview

Use double curly braces to evaluate an expression:

{{ expression }}

Expression rules:

• Plain text outside {{ ... }} is returned as-is.
• Function calls are space-separated: {{ functionName arg1 arg2 }}.
• Use double quotes for arguments with spaces: {{ lowercase "HELLO WORLD" }}.
• Nested calls use parentheses: {{ uppercase (lowercase "MiXeD") }}.
• If an expression fails, output is rendered as: {{ERROR: ...}}.

Data Source

Most templates read values from JSON runtime data through jsonPointer.

Example runtime JSON:

{
	"project": {
		"name": "Nara",
		"version": 12,
		"active": true,
		"tags": ["vision", "flow"]
	},
	"node": {
		"id": "node-07"
	}
}

Data Function: jsonPointer

jsonPointer fetches a value from JSON (e.g. node output) using a JSON Pointer path.

{{ jsonPointer pointer }}
{{ jsonPointer pointer indent }}

Arguments:

• pointer (required): JSON Pointer path, for example "/project/name".
• indent (optional): integer indentation for pretty JSON output when target is object/array.

Behavior:

• String result: returns string value.
• Number result: converted to string.
• Boolean result: returns true or false.
• Null result: returns empty string.
• Object/array result:
  • no indent or indent = 0: compact JSON string.
  • indent > 0: pretty-printed JSON.

jsonPointer Examples

1. Read a string value:

Template: {{ jsonPointer "/project/name" }}
Output:   Nara

2. Read a numeric value:

Template: {{ jsonPointer "/project/version" }}
Output:   12

3. Read a boolean value:

Template: {{ jsonPointer "/project/active" }}
Output:   true

4. Read an array (compact JSON):

Template: {{ jsonPointer "/project/tags" }}
Output:   ["vision","flow"]

5. Read an array (pretty JSON):

Template: {{ jsonPointer "/project/tags" 2 }}
Output:
[
	"vision",
	"flow"
]

6. Chain with other functions:

Template: {{ uppercase (jsonPointer "/project/name") }}
Output:   NARA

7. Invalid path handling:

Template: {{ jsonPointer "/project/unknown" }}
Output:   {{ERROR: JSON pointer error: ...}}

jsonPointer and Data References (Flow runtime)

In flow execution, string values that match the internal data-reference prefix are resolved automatically:

• Frame reference in idFrames -> converted to Base64 string.
• Vector frame reference in idVFrames -> first frame converted to Base64.
• This resolution is recursive for objects and arrays returned by jsonPointer.

Practical effect:

• If JSON contains a data-reference token, jsonPointer can return encoded image content instead of the raw token.

String Functions

lowercase

Converts the first argument to lowercase.

{{ lowercase "Hello WORLD" }}

Output:

hello world

uppercase

Converts the first argument to uppercase.

{{ uppercase "Hello WORLD" }}

Output:

HELLO WORLD

capitalize

Uppercases only the first character of the first argument.

{{ capitalize "nara flow" }}

Output:

Nara flow

Padding Function

stringPad

Pads a string to target length.

{{ stringPad value targetLength padToken direction }}

Arguments:

• value (required): source string.
• targetLength (required): non-negative integer.
• padToken (optional): token used for padding, default is single space.
• direction (optional): start or end, default is start.

Examples:

{{ stringPad "7" 3 "0" "start" }}

Output:

007

{{ stringPad "ID" 6 "-" "end" }}

Output:

ID----

{{ stringPad "ABC" 8 "xy" "end" }}

Output:

ABCxyxyx

Errors:

• Missing required args -> error.
• Non-numeric length -> error.
• Negative length -> error.
• Invalid direction (not start or end) -> error.

Date and Context Functions

datetimeNow

Returns current local datetime.

{{ datetimeNow }}
{{ datetimeNow "ISO_EXT_DATE_TIME_MILLISEC" }}

Notes:

• If no format is provided, default format is ISO_EXT_DATE_TIME_MILLISEC.
• If format text is unknown, it falls back to the same default.

Example output:

2026-05-23T15:04:12.381

toolId

Returns current flow tool ID from runtime context.

{{ toolId }}

Example output:

tool-image-segmentation

nodeId

Returns current flow node ID from runtime context.

{{ nodeId }}

Example output:

node-07

Nested Expression Examples

{{ uppercase (jsonPointer "/project/name") }}

{{ stringPad (jsonPointer "/project/version") 4 "0" "start" }}

{{ capitalize (lowercase "NARA TEMPLATE") }}

Troubleshooting

• Unknown function: ...
  • Function name is not registered in current runtime.
• jsonPointer function requires at least one argument
  • Missing pointer path.
• JSON pointer error: ...
  • Invalid path or path does not exist.
• stringPad function requires a numeric length argument
  • Target length is not an integer.