# Merge URL: /reference/blocks/system-merge Type: reference Description: Reconnect branches after a Condition or Router. Runs when at least one predecessor executed; passes through the active branch's output. Keywords: merge, system/merge, system, block, workflow builder `system/merge` — Reconnect branches after a Condition or Router. Runs when at least one predecessor executed; passes through the active branch's output. Where it appears [#where-it-appears] The **Merge** block lives in the **Logic & control** group of the Workflow Builder. Fields [#fields] This block has no configurable fields. Inputs and outputs [#inputs-and-outputs] Inputs are the configurable fields above. The block produces these outputs: **Outputs** Reference an output downstream with ``. | Name | Type | Description | | ----------------- | ------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `success` | boolean | True when at least one predecessor executed successfully. False is never observed in practice — the block is skipped if all predecessors were skipped. | | `source` | string | Node id of the predecessor whose output is exposed via `data`. When multiple predecessors executed, the topologically-first one wins. | | `data` | json | Pass-through of the selected predecessor's `data` field, or its full output object if the predecessor did not declare a `data` output. | | `executedSources` | array | Node ids of all predecessors that executed, in topological order. Useful for observability and for downstream function blocks that need to know which branches fired. | Related [#related] * [All workflow blocks](/reference/blocks) * [Workflow Builder overview](/workflow-builder-overview)