---
title: HostInjectedInput
description: The fields that jr2 adds to the input of the Machine that a run starts, beside the input that the caller sent.
---

# `HostInjectedInput`

Type, in `@jr2/orchestrator/src/vocabulary.ts`. It is an export of `@jr2/orchestrator`, on the [Authoring surface](../authoring-surface.md) page, in Machine and events.

```ts
type HostInjectedInput = { instanceId: string };
```

The fields that jr2 adds to the input of the Machine that a run starts, beside the input that
the caller sent. Today it is one field: `instanceId`, an id that jr2 makes for the run.

Add it to the type of your root Machine's input when the Machine reads it:
`HostInjectedInput & RunInput`. Do not put it in the `input` schema that a run starts with. No
caller sends it. jr2 writes it over any value that a caller sends.

Only the root Machine of a run gets it. A Machine that another Machine invokes gets the input
that its parent gives it. A `workspace()` passes its input to its body, so the body of a root
`workspace()` gets it too: `Workspaced<HostInjectedInput & RunInput, "app">`.

The `spec` of a root `workspace()` also gets it, and the type of its input shows it:
``spec: ({ input }) => ({ branch: `fix/${input.instanceId}` })``.

It is not the run id. Use it, for example, to give each run a branch of its own.

**Fields**

- `instanceId`: `string`

**Example**

```ts
import { z } from "zod";
import { jr2Setup, type HostInjectedInput } from "@jr2/orchestrator";

const runInput = z.object({ ticket: z.string() });
type Input = HostInjectedInput & z.infer<typeof runInput>;

export const machine = jr2Setup({
  types: {} as { input: Input; context: Input; output: { run: string; ticket: string } },
}).createMachine({
  id: "ticket",
  input: runInput,
  context: ({ input }) => input,
  initial: "done",
  states: { done: { type: "final" } },
  output: ({ context }) => ({ run: context.instanceId, ticket: context.ticket }),
});
```

**See also**

- [Write a Workflow](../../guides/write-a-workflow.md)
- [ADR-0033: A Machine declares the input that starts it](../decisions/0033-a-machine-declares-the-input-that-starts-it.md)