vellum.workflows.nodes.ToolCallingNode
Used to execute a repeatedly invoke a prompt with defined tools until it produces a text output.
Optional inputs for variable substitution in the prompt. These inputs are used to replace:
blocks attributeYou can reference either Workflow inputs or outputs from upstream nodes.
The blocks that make up the Prompt
The model to use for execution (e.g., “gpt-5”, “claude-4-sonnet”)
The tools that a the Prompt has access to and automatically invokes on each iteration. The acceptable tool types are:
Callable[..., Any] - Any function callableType["BaseWorkflow"] - An Inline SubworkflowDeploymentDefinition - A reference to a Vellum Workflow DeploymentModel parameters for execution. Defaults to:
json_schema (learn more here).The maximum number of iterations that the Tool Calling Node is allowed to call the underlying Prompt before rejecting.
The generated text output from the last prompt execution
The array of chat messages produced over the course of the Tool Calling Node’s iterations.
If you are planning to move between the UI and your IDE, you should use the following folder structure: