Composition

How one call becomes a reusable operation, an entry point or a graph: Functions, Endpoints, Workflows, node types and triggers. Each page below is one RFC of the w6w specification.

• Function
• Endpoint
• Workflow
• Node Types
• Trigger

Fan-out and merge

A step can have more than one outgoing edge. fanOut on the step says how those branches run:

• "sequential" (the default) — branches run one after another, in plan order.
• "parallel" — branches run concurrently. The run waits for all of them, and a downstream step with several inbound edges runs once, after every branch has arrived.

Use the @w6w/control merge step to join branches back into one value. mode is "array" (the branch outputs in incoming-edge order) or "object" (outputs shallow-merged, the later edge wins). Optional entries ({ key?, value }) pick exactly what goes in; without entries, merge behaves as aggregate. If an entry’s value is a single reference, its type is preserved rather than turned into a string. An entry (its key or value) that reads a vault secret is refused, and the merge step fails with a parameter error, because merge output is stored with the run.

{
  "steps": [
    { "id": "start", "uses": { "app": "@w6w/trigger", "action": "trigger" }, "fanOut": "parallel" },
    { "id": "a", "uses": { "app": "crm", "action": "getUser", "connection": "conn_crm" } },
    { "id": "b", "uses": { "app": "billing", "action": "getPlan", "connection": "conn_bill" } },
    {
      "id": "join",
      "uses": { "app": "@w6w/control", "action": "merge" },
      "with": {
        "mode": "object",
        "entries": [
          { "key": "user", "value": { "$": "steps.a.output" } },
          { "key": "plan", "value": { "$": "steps.b.output" } }
        ]
      }
    }
  ],
  "edges": [
    { "from": "start", "to": "a" }, { "from": "start", "to": "b" },
    { "from": "a", "to": "join" }, { "from": "b", "to": "join" }
  ]
}

See the Workflow and Engine RFC amendments of 2026-10-07 for the exact semantics.