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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:

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'
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:

version: 1.0.0
sections:
  main:
    - answer: {}
    - ai:
        prompt:
          text: |
            You help users search for information.
            When they ask a question, use the search function.
        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:

version: 1.0.0
sections:
  main:
    - answer: {}
    - ai:
        prompt:
          text: |
            You are a call logging assistant.
            Use the log function to record this call.
        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:

version: 1.0.0
sections:
  main:
    - answer: {}
    - ai:
        prompt:
          text: |
            You provide caller information to users.
            Use the format_number function to format phone numbers.
        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:

version: 1.0.0
sections:
  main:
    - answer: {}
    - ai:
        prompt:
          text: |
            You are a pricing assistant.
            Use the calculate function to compute discounts.
        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:

version: 1.0.0
sections:
  main:
    - answer: {}
    - ai:
        prompt:
          text: |
            You help debug user input.
            Use the debug function to echo values.
        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:

version: 1.0.0
sections:
  main:
    - answer: {}
    - ai:
        prompt:
          text: |
            You provide confirmation codes to users.
            Use the spell_code function to spell out codes.
        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:

version: 1.0.0
sections:
  main:
    - answer: {}
    - ai:
        prompt:
          text: |
            You handle rate-limited operations.
            Use the delayed_task function when needed.
        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:

version: 1.0.0
sections:
  main:
    - answer: {}
    - ai:
        prompt:
          text: |
            You help users search for information.
            When they ask a question, use the search function.
        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}"