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

# Hello World Agent Application

> A minimal Agent Application: one persistent notebook agent, one durable workspace, and work that continues across runs.

# Hello World: a durable notebook

The smallest useful Agent Application can return to work it saved during an
earlier run. A one-shot task runner cannot.

This example is a notebook agent for one user. It saves notes in its workspace
and maintains a short briefing that the user can open without reading through
the conversation.

```text theme={null}
durable-notebook/
|-- instructions.md
|-- tools/
|   `-- save-note.ts
`-- agentapplication.yaml
```

## The program

`instructions.md` contains the behavior written in natural language:

```markdown theme={null}
You maintain a research notebook for one user.

When the user asks you to remember something, append it to notes.md with the
date and source. When asked for a briefing, read notes.md and update briefing.md.
Never remove an earlier note unless the user asks you to.
```

`save-note.ts` provides the deterministic file operation:

```ts theme={null}
import { appendFile } from "node:fs/promises";

export async function saveNote(text: string) {
  await appendFile("notes.md", `- ${new Date().toISOString()}: ${text}\n`);
  return { saved: "notes.md" };
}
```

The deployment declaration asks for a persistent workspace and uses the user ID
as the instance key:

```yaml theme={null}
apiVersion: agentapplication.io/v0alpha1
kind: AgentApplication

metadata:
  name: durable-notebook

instance:
  key: user.id

workspace:
  durability: required
  isolation: per-instance

artifacts:
  - path: briefing.md
```

This is the portable contract proposed by the paper. A framework can express
the same requirements in its own format.

## Two runs, one continuing instance

On Monday, Ada says, "Remember that the launch moved to September 18." The
platform routes the request to Ada's notebook instance. The agent writes the
fact to `notes.md`, then the runtime suspends.

On Friday, Ada asks for a launch briefing. The platform wakes the same instance
and restores its workspace. The agent reads Monday's note and writes
`briefing.md`. Ada can open that file directly, share it, or return next week and
ask the agent to revise it.

| Defining property               | Where it appears                                                                                        |
| ------------------------------- | ------------------------------------------------------------------------------------------------------- |
| Persistent agent instance       | Ada's stable instance key selects the same notebook on every run and keeps it separate from other users |
| Durable computational workspace | `notes.md`, `briefing.md`, and the agent's instructions survive suspension                              |
| Durable work                    | The notes and briefing outlive the conversations that created them                                      |