Dynamic variables

Dynamic variables are placeholders written as {{name}}. Tried replaces them with string values at run time, so one agent can greet each caller by name, quote their appointment time or call a different API per customer.

Hi {{first_name}}, this is Ava from {{business_name}}. I'm calling about your appointment on {{appointment_date}}.

Syntax#

• Write {{name}}. Spaces inside the braces are allowed: {{ name }}.
• Names can use letters, numbers, _, ., +, / and -.
• Values are strings. Numbers and booleans you pass are converted to text.
• A variable with no value is left as written, braces included. The agent would read "{{first_name}}" aloud, so always set a default for variables a prompt depends on.
• Variables are not nested: a value that itself contains {{...}} is not expanded again.

In the prompt editor, type {{ to open Insert variable.

Where variables work#

Set values#

Defaults on the agent#

Security & Fallback Settings, Default Dynamic Variables sets values used when a call does not provide one. They are stored in default_dynamic_variables on the Retell LLM or conversation flow.

Per call through the API#

Pass retell_llm_dynamic_variables when you start a call:

curl https://api.tried.com.au/v2/create-phone-call \
  -H "Authorization: Bearer $TRIED_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from_number": "+61355505030",
    "to_number": "+61412555019",
    "retell_llm_dynamic_variables": { "first_name": "Sam", "appointment_date": "Tuesday the 21st at 4pm" }
  }'

await fetch("https://api.tried.com.au/v2/create-phone-call", {
  method: "POST",
  headers: { Authorization: `Bearer ${process.env.TRIED_API_KEY}`, "Content-Type": "application/json" },
  body: JSON.stringify({
    from_number: "+61355505030",
    to_number: "+61412555019",
    retell_llm_dynamic_variables: { first_name: "Sam", appointment_date: "Tuesday the 21st at 4pm" },
  }),
});

import os, requests

requests.post(
    "https://api.tried.com.au/v2/create-phone-call",
    headers={"Authorization": f"Bearer {os.environ['TRIED_API_KEY']}"},
    json={
        "from_number": "+61355505030",
        "to_number": "+61412555019",
        "retell_llm_dynamic_variables": {"first_name": "Sam", "appointment_date": "Tuesday the 21st at 4pm"},
    },
)

The same field is accepted by Create web call, Register phone call, each task of a batch call, and chats. In a batch CSV, every column after the phone number becomes a variable.

Inbound calls#

For inbound calls, the number's inbound webhook can return variables before the agent answers, and a pre-call workflow can fetch them. Inbound SIP headers that start with X-, plus Diversion, History-Info, P-Asserted-Identity and User-to-User, become variables named after the header in lower case, such as {{x-customer-id}}.

Contacts#

Phone calls are linked to a contact. The contact's fields become variables: {{first_name}}, {{last_name}}, {{contact_email}}, {{do_not_call}} and every custom field. With contact memory reading on, {{contact_memory}} holds the memory brief. See Contact memory.

Environment tags#

Each environment tag (such as prod or staging) can carry its own variable values, used by calls that run through that tag. See Versions and environments.

During the call#

Values collected during the call are added as they arrive:

• The Extract Dynamic Variable function, and extract nodes in flows.
• response_variables on custom, code, MCP and integration app functions, which copy fields from the result.
• Values passed with a multi-prompt transition.
• Replies to an SMS sent with an info-collection template.

They are stored on the call in collected_dynamic_variables.

On a live call#

Update live call sets override_dynamic_variables on an ongoing call. The agent sees them from the next turn.

curl -X PATCH https://api.tried.com.au/update-live-call/call_8d2f0c1e9b7a6543210fedcb \
  -H "Authorization: Bearer $TRIED_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "override_dynamic_variables": { "order_status": "shipped" } }'

Precedence#

When the same name is set in several places, the later source in this list wins:

1. Agent defaults (default_dynamic_variables)
2. Environment tag values
3. Contact fields
4. Values passed when the call was created (retell_llm_dynamic_variables, inbound webhook, pre-call workflow)
5. Values collected during the call
6. Live overrides from update-live-call

System variables are filled by the runtime and are always available.

System variables#

The timezone comes from the agent's Timezone under Agent Settings (default Australia/Sydney).

Read values after the call#

The call object has:

• retell_llm_dynamic_variables: the values the call started with.
• collected_dynamic_variables: the values captured during the call.

Use them in webhooks, analytics filters and QA cohorts. List calls can filter on variables with filter_criteria.fields and source: "dynamic_variable".

Test with variables#

The { } button in the test panel opens Dynamic variables. Values set there are used by Test LLM, Test Audio and the simulated caller.