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SWML Template Functions

Reference for built-in transformation functions

Template functions provide simple text transformations for common operations like converting to lowercase, URL encoding, and date formatting. They complement JavaScript expressions by handling specific formatting tasks that don't require complex logic.

For information about variable scopes, see the Variables Reference. For JavaScript expressions and data manipulation, see the Expressions Reference.

caution

Template functions are only available in SWAIG (SignalWire AI Gateway) contexts, specifically within:

  • AI function data_map processing (expressions, webhooks, output)
  • Webhook responses to SWAIG functions
  • AI prompt variable expansion

They are not available in regular SWML methods or general variable contexts. For regular SWML variable manipulation, use JavaScript expressions with the ${expression} syntax instead.

Available template functions​

lc
string

Converts a string to lowercase. Commonly used to normalize user input for case-insensitive comparisons or ensure consistent casing when accessing object properties dynamically.

Syntax: ${lc:<value>}

Example:

SWAIG:
  functions:
    - function: lookup
      description: Look up department contact
      parameters:
        type: object
        properties:
          department:
            type: string
            description: Department name from user
      data_map:
        expressions:
          - string: '${meta_data.contacts.${lc:args.department}}'
            pattern: '\w+'
            output:
              response: "Found contact for ${args.department}"
      meta_data:
        contacts:
          sales: '+12025551234'
          support: '+12025555678'
enc:url
string

Encodes a string for safe use in URLs by converting special characters to percent-encoded equivalents. Always use this when including variables in URL query parameters or paths to prevent special characters from breaking URLs or causing unexpected behavior.

Syntax: ${enc:url:<value>}

Example:

SWAIG:
  functions:
    - function: search
      description: Search external knowledge base
      parameters:
        type: object
        properties:
          query:
            type: string
            description: User's search query
      data_map:
        webhooks:
          - url: 'https://api.example.com/search?q=${enc:url:args.query}'
            method: GET
            output:
              response: "Found ${results.total} results for ${args.query}"
strftime_tz
string

Formats the current date and time using standard strftime format codes with timezone support. This generates timestamps at the moment the template is evaluated, not when the SWML script was created.

Syntax: @{strftime_tz <timezone> <format>}

Common format codes:

  • %Y-%m-%d - ISO date (2025-01-15)
  • %H:%M:%S - 24-hour time (14:30:45)
  • %I:%M %p - 12-hour time (02:30 PM)
  • %A, %B %d, %Y - Full readable date (Monday, January 15, 2025)

Example:

SWAIG:
  functions:
    - function: log_call
      description: Log call details with timestamp
      data_map:
        webhooks:
          - url: 'https://api.example.com/logs'
            method: POST
            params:
              timestamp: '@{strftime_tz America/Chicago %Y-%m-%d %H:%M:%S}'
              call_id: '${call.call_id}'
              from: '${call.from}'
            output:
              response: "Call logged successfully"
fmt_ph
string

Formats a phone number using specified international format standards. Supports multiple format types for different use cases, with optional separators for improved text-to-speech pronunciation.

Syntax: @{fmt_ph <format> <phone_number>} or @{fmt_ph <format>:sep:<separator> <phone_number>}

Available formats:

  • national - National format (default)
  • international - International format with country code
  • RFC3966 - RFC 3966 format (tel: URI)
  • e164 - E.164 format (+1234567890)

Example:

SWAIG:
  functions:
    - function: format_number
      description: Format phone number for speech
      data_map:
        output:
          response: |
            International format: @{fmt_ph international ${call.from}}
            Spaced format: @{fmt_ph national:sep:- ${call.from}}
expr
string

Evaluates simple arithmetic expressions with literal numbers. Supports addition, subtraction, multiplication, division, and parentheses for grouping. Only works with literal numbers and cannot reference variables.

Syntax: @{expr <expression>}

Example:

SWAIG:
  functions:
    - function: calculate_discount
      description: Calculate discount amount
      data_map:
        output:
          response: "The discount is @{expr (100 - 25) / 5} dollars"
echo
string

Returns the argument unchanged. Primarily useful for debugging template evaluation or forcing explicit variable expansion in complex nested scenarios.

Syntax: @{echo <text>}

Example:

SWAIG:
  functions:
    - function: debug_value
      description: Debug template evaluation
      parameters:
        type: object
        properties:
          input:
            type: string
            description: Value to debug
      data_map:
        output:
          response: "Debug value: @{echo ${args.input}}"
separate
string

Inserts spaces between each character in a string to improve text-to-speech pronunciation. Particularly useful for spelling out confirmation codes, license plates, serial numbers, or any text that should be read character-by-character.

Syntax: @{separate <text>}

Example:

SWAIG:
  functions:
    - function: spell_code
      description: Spell out confirmation code
      parameters:
        type: object
        properties:
          code:
            type: string
            description: Confirmation code to spell
      data_map:
        output:
          response: "Your code is @{separate ${args.code}}"

In this example, if code is "ABC123", the AI will pronounce "A B C 1 2 3" instead of trying to say "ABC123" as a word.

sleep
string

Pauses execution for the specified number of seconds. Can be used for rate limiting, timing coordination, or testing purposes.

Syntax: @{sleep <seconds>}

caution

Use sparingly in production environments. Excessive delays can cause timeouts, impact call quality, and degrade user experience. Best suited for development, testing, or specific rate-limiting scenarios.

Example:

SWAIG:
  functions:
    - function: delayed_task
      description: Execute with delay for rate limiting
      data_map:
        output:
          response: "Executed after @{sleep 2} second delay"

Function chaining​

Prefix functions (using ${...} syntax) can be chained together to apply multiple transformations in sequence. The transformations are applied from left to right.

Syntax: ${func1:func2:func3:<value>}

Example:

SWAIG:
  functions:
    - function: search
      description: Search external knowledge base
      parameters:
        type: object
        properties:
          query:
            type: string
            description: User's search query
      data_map:
        webhooks:
          # First converts to lowercase, then URL encodes
          - url: 'https://api.example.com/search?q=${lc:enc:url:args.query}'
            method: GET
            output:
              response: "Found results for ${args.query}"

Full example​

version: 1.0.0
sections:
  main:
    - answer: {}
    - ai:
        prompt:
          text: |
            You help users access department resources.
            When they specify a department, use the lookup function.
        SWAIG:
          functions:
            - function: lookup
              description: Look up department contact
              parameters:
                type: object
                properties:
                  department:
                    type: string
                    description: Department name from user
              data_map:
                expressions:
                  - string: '${meta_data.contacts.${lc:args.department}}'
                    pattern: '\w+'
                    output:
                      response: "Found contact for ${args.department}"
              meta_data:
                contacts:
                  sales: '+12025551234'
                  support: '+12025555678'