Variables and Placeholders

Variables insert live values into agent prompts, start messages, API request payloads, webhook payloads, and post-call email or SMS templates. The available names and missing-value behaviour depend on where the template is used.

Give an agent the current time

Add an IANA timezone variable directly to the system prompt. It is evaluated when the prompt is sent to the model, so the agent receives the live value rather than the text of the placeholder. Replace Europe/London with the timezone the agent should use.

The current date and time is {{current_datetime:Europe/London}}.
Use this value whenever the caller asks for the current date or time.

Timezone variables also work in start messages and are recalculated for every new conversation.

{{greeting:Europe/London}}. The time is {{current_time:Europe/London}}. How can I help?

Syntax and resolution

Write a variable as two opening braces, its exact name, and two closing braces. Spaces immediately inside the braces are accepted, but using the autocomplete picker avoids spelling mistakes.

• Prompt and start-message variables include timezone-qualified names such as {{current_time:Europe/London}} and flat call-context names such as {{customer_number}}.
• Tool and webhook payload variables use namespaced paths such as {{call.from_number}} or {{summary.sentiment}}.
• Names are case-sensitive in prompts and post-call templates. Request-payload paths are resolved case-insensitively.
• An unavailable value is not guessed. See the final section for the exact missing-value behaviour on each surface.

Any IANA timezone

Voice-agent prompts and start messages can calculate a value in any valid IANA timezone. Put the timezone after a colon, as shown below. Replace the example timezone with the required IANA name; daylight-saving changes are handled automatically.

The current time in Tokyo is {{current_datetime:Asia/Tokyo}}.

Invalid IANA timezone names are logged and resolve to an empty value rather than using a guessed timezone.

Legacy fixed-region aliases

Use the IANA timezone format above for new agents. These older UK and US aliases remain available so existing prompts and start messages continue to work.

The additional legacy aliases {{current_date_gb}}, {{current_time_gb}}, and {{current_datetime_gb}} return the same values as their _uk equivalents.

Voice-call variables

These values are populated from the active voice or SIP call. They are not available to a standalone chat-agent session.

Custom call and campaign variables

Any valid call metadata key can be referenced as a flat prompt or start-message variable. Reserved built-in call variables take priority over metadata with the same name.

• Test and preview calls detect custom placeholders in the prompt and start message and ask you to enter their values before the call starts.
• API and manual outbound calls can supply metadata; each key becomes a prompt variable for that call.
• Browser test links accept a vars JSON object or repeated var.name query parameters.
• Campaign contact fields and contact metadata become variables for that contact's call.

Snake-case metadata also gets a camelCase alias. For example, customer_reference is available as both {{customer_reference}} and {{customerReference}}. When a name is available, {{firstName}} and {{first_name}} contain the first name after removing a common title; {{greetingName}} contains that first name or the fallback value there.

Hi {{greetingName}}, your reference is {{reference}}.

Tool request variables

Custom tool payloads use the following namespaces. Tool parameters are chosen by the model from the configured parameter schema; trusted call context overrides a model-supplied value when both use the same key.

Wrap a payload path as {{base64(parameters.example)}} to Base64-encode that value. A placeholder used as the whole JSON field preserves arrays, objects, booleans and numbers; a placeholder embedded in text becomes a string.

Webhook request variables

Custom webhook payloads expose the final call, summary, extracted fields and delivery context through these namespaces. Post-conversation values are not available to pre-conversation or during-conversation requests.

Post-call email and SMS variables

Email subjects, email bodies, recipient addresses, SMS recipients and SMS bodies use flat placeholders. Summary-derived values are available only after the conversation summary has been generated.

List values use the _list suffix and are inserted as comma-separated text. The valid names are {{key_topics_list}}, {{action_items_list}}, {{symptoms_list}}, {{steps_taken_list}}, {{recommendations_list}}, and {{next_steps_list}}; {{key_topics}} and {{action_items}} are not post-call template variables.

Availability and missing values

• Clock values are calculated at execution time, not when the template is saved.
• Voice-call values are empty when the underlying SIP or call context does not provide them. Unknown placeholders in a spoken start message are removed before speech.
• Before and during-conversation post-call actions cannot use summary-derived or AI-extracted values because the final conversation does not yet exist.
• In a custom tool or webhook JSON payload, a missing whole-field placeholder becomes null. A missing placeholder embedded inside text becomes an empty string.
• Unknown prompt placeholders remain visible in a system prompt, so verify spelling and supply every custom value. Test calls prompt for custom values they detect.