Service Composition (Workflow-to-Workflow Calls)

Service Composition (Workflow-to-Workflow Calls)

Service composition allows one workflow (caller) to invoke another workflow (callee) through the Execute Workflow node. This enables modular design and reusable workflow components.

The Concept:

Caller Workflow:

1. Step 1
2. Execute Workflow Node → triggers Callee
3. Step 3

Callee Workflow:

1. Trigger Node (receives call)
2. Step A

The callee runs as its own webhook execution, billed to the callee owner's budget (owner-pays). The caller's budget is not charged for the callee — there is no second charge against the caller.

What Is Service Composition?

Instead of building one giant workflow, you can break your automation into smaller, reusable pieces:

This is the technical foundation of "workflows calling workflows."

How It Works

The Flow

Webhook Registry

The system maintains a reverse index to resolve callees:

Registry Key: instance:{chainId}:{address}:{tokenId}Registry Value: Webhook path for ExecuteWorkflowTrigger

When a workflow registers its webhook URL, it's stored for later lookup by other workflows.

Callee Requirements

For a workflow to be callable:

Billing Model

The callee runs as its own webhook execution, billed to the callee owner's budget (owner-pays). The caller's budget is not charged for the callee, and there is no second settlement against the caller:

Billing Example:

• Caller execution: $0.01 — paid from the caller's budget to the caller's builder
• Callee execution: $0.15 — paid from the callee owner's budget to the callee's builder
• The caller is charged only $0.01; the callee's $0.15 is not deducted from the caller's budget

A sub-workflow that runs in-process under the parent run (same execution) is a single charge — it is never billed separately.

Related

• Execute Workflow Trigger
• Technical Architecture
• Pricing & Fees Reference