Guides

Node reference

Every node type available in the Vollo workflow builder — its configuration fields, defaults, and output handles. Nodes are grouped into seven categories. This reference matches workflow schema version 1.

Nodes are connected by edges from an output handle on the source node to the input of the target node. Most nodes have a single next output; branching nodes expose one handle per outcome (for example true/false, or answered/no_answer/failed), and a few build their handles dynamically from configuration. Fields typed template accept {{variable}} interpolation; fields typed expression use the safe expression grammar.

Flow

7 nodes

Voice

6 nodes

AI

7 nodes

Data

4 nodes

Integrations

5 nodes

Knowledge

3 nodes

Telephony

5 nodes

Flow#

Start#

type: start · min 1 per workflow · max 1 per workflow

Entry point of every workflow. Execution begins here when a call is answered or a session connects. Exactly one per workflow.

Outputs

This node has no configuration fields.

End#

type: end

Terminates the workflow cleanly. The session or call is wrapped up and a workflow.completed event is emitted.

Outputs

terminal — no outputs

This node has no configuration fields.

Branch#

type: branch

Routes execution down one of several labeled branches. Each branch has an expression; the first branch whose condition evaluates to true wins.

Outputs

dynamic

Output handles are created from the node's configuration (one per branch, intent, case, or exit intent).

Field	Type	Required	Default	Notes
`branches`	`array`	Required	—	At least 2 items. Each item: `key`, `label`, `condition`.
`default_branch`	`string`	Optional	—	—

Condition#

type: condition

Evaluates a single expression and routes to the true or false handle.

Outputs

truefalse

Field	Type	Required	Default	Notes
`expression`	`expression`	Required	—	—

Switch#

type: switch

Compares a variable against a list of case values and routes to the matching case's handle, with an optional default.

Outputs

dynamic

Output handles are created from the node's configuration (one per branch, intent, case, or exit intent).

Field	Type	Required	Default	Notes
`variable`	`string`	Required	—	—
`cases`	`array`	Required	—	At least 1 item. Each item: `value`, `label`.
`default_case`	`boolean`	Optional	`true`	—

Delay#

type: delay

Pauses workflow execution for a fixed number of seconds without playing audio.

Outputs

Field	Type	Required	Default	Notes
`seconds`	`number`	Required	—	Min 0.1 · max 300.

Loop#

type: loop

Repeats the subgraph connected to its loop handle until the exit condition is true or the iteration cap is reached, then continues via done.

Outputs

loopdone

Field	Type	Required	Default	Notes
`max_iterations`	`number`	Required	—	Min 1 · max 100.
`exit_condition`	`expression`	Optional	—	—

Voice#

Greeting#

type: greeting

Speaks an opening line as soon as the node is reached. By default it cannot be barged in on, so the caller hears the full greeting.

Outputs

Field	Type	Required	Default	Notes
`text`	`template`	Required	—	—
`interruptible`	`boolean`	Optional	`false`	—

Speak#

type: speak

Synthesizes and plays a text-to-speech utterance. Interruptible by default so callers can barge in.

Outputs

Field	Type	Required	Default	Notes
`text`	`template`	Required	—	—
`interruptible`	`boolean`	Optional	`true`	—
`voice_override`	`string`	Optional	—	—

Listen#

type: listen

Captures one user utterance via speech-to-text and stores the transcript in a variable.

Outputs

Field	Type	Required	Default	Notes
`save_to_variable`	`string`	Required	—	—
`timeout_seconds`	`number`	Optional	`10`	Min 1 · max 120.
`language`	`string`	Optional	—	—

Wait#

type: wait

Keeps the line open in silence for a fixed interval — useful after asking the caller to find something.

Outputs

Field	Type	Required	Default	Notes
`seconds`	`number`	Required	—	Min 0.5 · max 60.

Transfer to Human#

type: transfer

Attempts a warm transfer of the live conversation to a human at a phone number or SIP URI.

Outputs

transferredfailed

Field	Type	Required	Default	Notes
`destination`	`template`	Required	—	tel:+E164 or SIP URI.
`announcement`	`template`	Optional	—	—
`play_dialtone`	`boolean`	Optional	`true`	—

Hangup#

type: hangup

Ends the call or session, optionally speaking a farewell first.

Outputs

terminal — no outputs

Field	Type	Required	Default	Notes
`farewell`	`template`	Optional	—	—

AI#

Agent#

type: agent

Runs a full conversational AI agent — LLM, speech-to-text, and text-to-speech — either referencing a saved Agent or configured inline. Each exit intent you define becomes an output handle the LLM can signal to leave the node.

Outputs

dynamic

Output handles are created from the node's configuration (one per branch, intent, case, or exit intent).

Field	Type	Required	Default	Notes
`agent_id`	`agent_ref`	Optional	—	Reference a saved Agent, or configure inline.
`system_prompt`	`template`	Required unless `agent_id` is set	—	—
`llm_provider`	`enum`	Optional	—	One of `openai`, `anthropic`, `google`, `openrouter`.
`llm_model`	`string`	Optional	—	—
`temperature`	`number`	Optional	—	Min 0 · max 2.
`stt_provider`	`enum`	Optional	—	One of `deepgram`.
`stt_language`	`string`	Optional	—	—
`tts_provider`	`enum`	Optional	—	One of `cartesia`.
`tts_voice`	`string`	Optional	—	—
`tools`	`tool_refs`	Optional	—	—
`knowledge_base_ids`	`knowledge_refs`	Optional	—	—
`mcp_server_ids`	`mcp_refs`	Optional	—	—
`greeting`	`template`	Optional	—	—
`max_turns`	`number`	Optional	—	Min 1 · max 200.
`timeout_seconds`	`number`	Optional	—	Min 10 · max 3600.
`exit_intents`	`array`	Optional	—	Each item: `key`, `label`, `description`. Each exit intent becomes an output handle; the LLM signals it via an exit tool.

Handoff#

type: handoff

Transfers the conversation to a different saved Agent, optionally summarizing the conversation so far as context for the receiving agent.

Outputs

Field	Type	Required	Default	Notes
`target_agent_id`	`agent_ref`	Required	—	—
`context_summary`	`boolean`	Optional	`true`	Summarize conversation for the receiving agent.
`announcement`	`template`	Optional	—	—

LLM Completion#

type: llm

Makes a single non-conversational LLM completion call and stores the result in a variable. Nothing is spoken.

Outputs

Field	Type	Required	Default	Notes
`prompt`	`template`	Required	—	—
`system_prompt`	`template`	Optional	—	—
`provider`	`enum`	Optional	—	One of `openai`, `anthropic`, `google`, `openrouter`.
`model`	`string`	Optional	—	—
`temperature`	`number`	Optional	—	Min 0 · max 2.
`save_to_variable`	`string`	Required	—	—
`json_mode`	`boolean`	Optional	`false`	—

Intent Detection#

type: intent

Classifies an utterance into one of your defined intents. Each intent becomes an output handle; unmatched input follows the fallback intent.

Outputs

dynamic

Output handles are created from the node's configuration (one per branch, intent, case, or exit intent).

Field	Type	Required	Default	Notes
`input_variable`	`string`	Optional	—	Defaults to the last user utterance.
`intents`	`array`	Required	—	At least 2 items. Each item: `key`, `label`, `description`.
`fallback_intent`	`string`	Optional	—	—
`save_to_variable`	`string`	Optional	—	—

Classification#

type: classification

Classifies the value of a variable into one of your defined classes and stores the winning class key.

Outputs

Field	Type	Required	Default	Notes
`input_variable`	`string`	Required	—	—
`classes`	`array`	Required	—	At least 2 items. Each item: `key`, `label`.
`save_to_variable`	`string`	Required	—	—

Summarization#

type: summarization

Summarizes the conversation so far (or a single variable) into a variable, capped at a word budget.

Outputs

Field	Type	Required	Default	Notes
`scope`	`enum`	Optional	`conversation`	One of `conversation`, `variable`.
`input_variable`	`string`	Required if `scope` is `variable`	—	—
`save_to_variable`	`string`	Required	—	—
`max_words`	`number`	Optional	`120`	Min 10 · max 500.

Sentiment#

type: sentiment

Scores the sentiment of the conversation (or a variable) and stores the result — positive, neutral, or negative.

Outputs

Field	Type	Required	Default	Notes
`scope`	`enum`	Optional	`conversation`	One of `conversation`, `variable`.
`input_variable`	`string`	Required if `scope` is `variable`	—	—
`save_to_variable`	`string`	Required	—	—

Data#

Set Variable#

type: set_variable

Assigns one or more variables. Values are templates, so they may interpolate other variables.

Outputs

Field	Type	Required	Default	Notes
`assignments`	`array`	Required	—	At least 1 item. Each item: `variable`, `value`.

Get Variable#

type: get_variable

Copies a variable (with an optional fallback default) into another variable.

Outputs

Field	Type	Required	Default	Notes
`variable`	`string`	Required	—	—
`save_to_variable`	`string`	Required	—	—
`default_value`	`string`	Optional	—	—

Transform#

type: transform

Applies a built-in transformation — case changes, trimming, type coercion, JSON encode/decode, digit extraction, or E.164 normalization — to a variable.

Outputs

Field	Type	Required	Default	Notes
`input_variable`	`string`	Required	—	—
`operation`	`enum`	Required	—	One of `uppercase`, `lowercase`, `trim`, `number`, `boolean`, `json_parse`, `json_stringify`, `extract_digits`, `e164`.
`save_to_variable`	`string`	Required	—	—

JSON Path#

type: json

Extracts a value from a JSON variable using a dot path and stores it in a variable.

Outputs

Field	Type	Required	Default	Notes
`input_variable`	`string`	Required	—	—
`path`	`string`	Required	—	Dot path, e.g. data.items.0.name.
`save_to_variable`	`string`	Required	—	—
`default_value`	`string`	Optional	—	—

Integrations#

HTTP Request#

type: http_request

Calls an external HTTP API. Response fields can be mapped into workflow variables; failures route to the error handle.

Outputs

successerror

Field	Type	Required	Default	Notes
`method`	`enum`	Required	—	One of `GET`, `POST`, `PUT`, `PATCH`, `DELETE`.
`url`	`template`	Required	—	—
`headers`	`key_value`	Optional	—	—
`query`	`key_value`	Optional	—	—
`body`	`template`	Optional	—	—
`body_type`	`enum`	Optional	`json`	One of `json`, `form`, `raw`.
`timeout_seconds`	`number`	Optional	`10`	Min 1 · max 60.
`retries`	`number`	Optional	`0`	Min 0 · max 5.
`auth`	`enum`	Optional	`none`	One of `none`, `bearer`, `basic`, `header`.
`auth_secret_key`	`secret_ref`	Required unless `auth` is `none`	—	—
`response_mapping`	`array`	Optional	—	Each item: `path`, `variable`.
`save_status_to`	`string`	Optional	—	—

Webhook#

type: webhook

Posts a JSON payload to your endpoint mid-workflow. Defaults to the standard event envelope and supports HMAC signing.

Outputs

successerror

Field	Type	Required	Default	Notes
`url`	`template`	Required	—	—
`payload`	`template`	Optional	—	JSON template; defaults to the standard event envelope.
`headers`	`key_value`	Optional	—	—
`auth`	`enum`	Optional	`none`	One of `none`, `bearer`, `basic`, `header`, `hmac`.
`auth_secret_key`	`secret_ref`	Required unless `auth` is `none`	—	—
`timeout_seconds`	`number`	Optional	`10`	Min 1 · max 30.
`retries`	`number`	Optional	`2`	Min 0 · max 5.
`response_mapping`	`array`	Optional	—	Each item: `path`, `variable`.

Function Tool#

type: function

Invokes a saved Function Tool defined in your workspace and stores its result.

Outputs

successerror

Field	Type	Required	Default	Notes
`tool_id`	`tool_ref`	Required	—	—
`arguments`	`key_value`	Optional	—	—
`save_to_variable`	`string`	Optional	—	—

MCP Tool#

type: mcp_tool

Calls a named tool on a connected MCP server and stores its result.

Outputs

successerror

Field	Type	Required	Default	Notes
`mcp_server_id`	`mcp_ref`	Required	—	—
`tool_name`	`string`	Required	—	—
`arguments`	`key_value`	Optional	—	—
`save_to_variable`	`string`	Optional	—	—
`timeout_seconds`	`number`	Optional	`30`	Min 1 · max 120.

API Tool#

type: api_tool

Invokes a saved API Tool (a declaratively configured HTTP tool) and stores its result.

Outputs

successerror

Field	Type	Required	Default	Notes
`tool_id`	`tool_ref`	Required	—	—
`arguments`	`key_value`	Optional	—	—
`save_to_variable`	`string`	Optional	—	—

Knowledge#

Knowledge Search#

type: knowledge_search

Runs a semantic search against a knowledge base and stores the top matches. Routes to found or not_found.

Outputs

foundnot_found

Field	Type	Required	Default	Notes
`knowledge_base_id`	`knowledge_ref`	Required	—	—
`query`	`template`	Required	—	—
`top_k`	`number`	Optional	`4`	Min 1 · max 20.
`save_to_variable`	`string`	Required	—	—
`min_score`	`number`	Optional	—	Min 0 · max 1.

RAG Answer#

type: rag

Retrieves relevant knowledge-base passages and generates a grounded answer, optionally speaking it immediately.

Outputs

Field	Type	Required	Default	Notes
`knowledge_base_id`	`knowledge_ref`	Required	—	—
`question`	`template`	Required	—	—
`top_k`	`number`	Optional	`4`	Min 1 · max 20.
`save_to_variable`	`string`	Required	—	—
`speak_answer`	`boolean`	Optional	`false`	—

Document Search#

type: document_search

Searches a knowledge base at document granularity and stores the best match.

Outputs

foundnot_found

Field	Type	Required	Default	Notes
`knowledge_base_id`	`knowledge_ref`	Required	—	—
`query`	`template`	Required	—	—
`save_to_variable`	`string`	Required	—	—

Telephony#

Dial#

type: dial

Places an outbound leg to a phone number from one of your provisioned caller IDs and routes on the outcome.

Outputs

answeredno_answerfailed

Field	Type	Required	Default	Notes
`to_number`	`template`	Required	—	—
`from_phone_number_id`	`phone_number_ref`	Required	—	—
`timeout_seconds`	`number`	Optional	`30`	Min 5 · max 120.

Transfer Call#

type: transfer_call

Blind-transfers the active call to another destination via SIP.

Outputs

transferredfailed

Field	Type	Required	Default	Notes
`destination`	`template`	Required	—	—
`play_dialtone`	`boolean`	Optional	`true`	—

Collect DTMF#

type: dtmf

Collects DTMF keypad digits from the caller, ended by a terminator key or timeout.

Outputs

collectedtimeout

Field	Type	Required	Default	Notes
`prompt`	`template`	Optional	—	—
`num_digits`	`number`	Optional	`1`	Min 1 · max 32.
`terminator`	`string`	Optional	`#`	—
`timeout_seconds`	`number`	Optional	`10`	Min 1 · max 60.
`save_to_variable`	`string`	Required	—	—

Call Recording#

type: call_recording

Starts or stops recording of the active call.

Outputs

Field	Type	Required	Default	Notes
`action`	`enum`	Required	—	One of `start`, `stop`.

Call Status#

type: call_status

Snapshots the current call state (direction, numbers, duration so far) into a variable as JSON.

Outputs

Field	Type	Required	Default	Notes
`save_to_variable`	`string`	Required	—	—

Config field types#

The tables above use the following field types:

Type	Meaning
`string`, `number`, `boolean`	Plain scalar values.
`template`	Text with `{{variable}}` interpolation. See Templates.
`expression`	A safe boolean expression. See Expressions.
`enum`	One of a fixed set of values, listed in the Notes column.
`array`	A list of objects; the item shape is listed in the Notes column.
`key_value`	A map of string keys to template values (headers, query params, arguments).
`secret_ref`	The key of a workflow secret variable. The value is stored encrypted and never returned by the API.
`agent_ref`, `tool_ref`/`tool_refs`, `mcp_ref`/`mcp_refs`, `knowledge_ref`/`knowledge_refs`, `phone_number_ref`	The ID of a saved Agent, Function/API Tool, MCP server, knowledge base, or phone number in your workspace (plural forms accept a list).

Validation

Run POST /workflows/{id}/validate (or press Validate in the builder) to check a draft against these schemas before publishing. Unknown variables referenced by templates are reported as warnings; missing required fields, bad enum values, and out-of-range numbers are errors.