n8n-subworkflows

n8n Sub-workflows

A sub-workflow is a reusable function. An Execute Workflow Trigger declares typed inputs, the body does the work, and the last node returns the output. A caller invokes it through an Execute Workflow node like any other step.

That framing buys you the things functions buy you everywhere: encapsulation, reuse, testability, replaceability. It's the primary reuse mechanism in n8n, and it's badly underused. Without it, the same logic gets copy-pasted across workflows — then a bug gets fixed in two places, the third copy gets missed, and your "identical" copies quietly drift apart.

This skill is about when to reach for a sub-workflow, how to define its input/output contract so callers (and agents) can actually use it, how to call it correctly (all vs each, blocking vs fire-and-forget), and how to name it so it gets found instead of rebuilt.

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The two non-negotiables

Everything else is judgement. These two are not.

1. Search before you build

Before you write logic for a generic problem, check whether a sub-workflow already does it. The community MCP can't filter workflows by tag, so the name is the discovery surface:

n8n_list_workflows()                          # scan the library
n8n_get_workflow({ id: "<candidate>" })       # read its inputs/outputs + body

If something fits, use it and tell the user ("I found Subworkflow: Parse RFC2822 date — using that"). If nothing fits, build it with a discoverable name so the next search finds it. The discovery convention (verb-first prefixes) lives in NAMING_AND_DISCOVERY.md.

2. The Execute Workflow Trigger uses "Define Below" with typed fields — not passthrough

The trigger has two input modes. Default to "Define Below" with explicit typed fields. Define Below is the only mode that gives callers a schema to fill — it's what lets an AI agent pass values via $fromAI and what lets structured callers map fields cleanly. Passthrough has no schema, so the trigger can't be wired as a clean agent tool and structured callers have nothing to bind to.