> ## Documentation Index
> Fetch the complete documentation index at: https://docs.major.build/llms.txt
> Use this file to discover all available pages before exploring further.

# State and input

> Pass data between workflow nodes and define the input a workflow accepts.

As a workflow runs, each node's output is stored under its node id. The workflow's input is stored under `trigger.input`. Later nodes read these values in their `config.input`, `prompt`, `message`, `output`, `iterable`, and router conditions.

## Referencing state

There are three ways to read state:

| Form | Example | Behavior |
| - | - | - |
| `$state` | `{ "$state": "lookup_order.items.0.sku" }` | Looks up a value by path. Array indexes are allowed. A missing path fails the run. |
| `$expr` | `{ "$expr": "lookup_order.total > 1000" }` | Evaluates a [CEL](https://cel.dev) expression. A missing path evaluates to `null` instead of failing. |
| `{{ }}` | `"Order {{trigger.input.order_id}} is ready"` | Interpolates a value into a string. Use `{{json node_id.path}}` to insert an object or array as JSON. |

In a `$expr`, every node id is a variable, and a node that hasn't run yet is `null`. Besides standard CEL, you can use:

* `has(node_id.field)` to check whether an optional field is present.
* `coalesce(a, b, ...)` (2 to 5 arguments) to take the first non-null value.
* `count(x)` to count the items in a list.

```jsonc theme={null}
// Router branch: only large orders from new customers
{ "$expr": "lookup_order.total >= 1000 && !has(lookup_order.previous_order_id)" }

// Fallback value in an app_call input
{ "email": { "$expr": "coalesce(trigger.input.email, lookup_order.customer_email)" } }
```

## What each node outputs

| Node | Output |
| - | - |
| `agent_call` | The shape of its `output_schema`, or `{ "result": "<final message text>" }` without one. |
| `app_call` | The response body. A non-object body is wrapped as `{ "body": ... }`. |
| `human_approval` | `{ "choice": "...", "responded_by": "..." }`, plus `"timed_out": true` on timeout. |
| `for_each` | `item` and `index` inside the loop body, and `results` after it exits. |
| `router`, `join`, `wait` | Nothing worth referencing. |

## Workflow input

Every run has an input object at `trigger.input`. Where it comes from depends on how the run started:

| Started by | `trigger.input` |
| - | - |
| **Run now** | The values you enter before running. |
| [Schedule](/learn/triggers/schedules) | The literal `input` on the cron trigger. |
| [Connector event](/learn/triggers/connector-events) | The event payload, or the trigger's `input` projection of it. |
| [Webhook](/learn/triggers/webhooks) | The JSON request body, or the trigger's `input` projection of it. |

### input\_schema

Add an `input_schema` at the top of the definition to describe and validate the input. It's a standard JSON Schema whose root is an object. Mark required fields with `required`, and allow `null` with a type union such as `["string", "null"]`.

```jsonc theme={null}
"input_schema": {
  "type": "object",
  "properties": {
    "region": { "type": "string", "default": "US" },
    "limit": { "type": "integer", "default": 50 },
    "customer_email": { "type": ["string", "null"] }
  },
  "required": ["region"]
}
```

Before every run, Major fills in the schema's `default` values, merges the trigger's input over them (explicit values win, including `null`, and arrays replace arrays), and validates the result. Values aren't coerced, so `"50"` doesn't pass as an integer. If the input fails validation, **Run now** shows the error, and a triggered run is recorded as failed without running any nodes. Without an `input_schema`, the input is passed through as is.

With an `input_schema`, **Run now** shows a form for the input, and you can save the values you enter as the workflow's defaults.

## Next steps

<CardGroup cols={2}>
  <Card title="Nodes" icon="diagram-project" href="/learn/workflows/nodes">
    Every node type and its fields.
  </Card>

  <Card title="Triggers" icon="bolt" href="/learn/triggers/overview">
    Start a workflow and shape its input.
  </Card>
</CardGroup>