---
title: "Primitives"
description: "Primitives are the building blocks a Flow uses. Each one belongs to a Flow."
canonical_url: "https://docs.superdurable.io/concepts/primitives/"
source: "docs/content/concepts/primitives/index.mdx"
locale: "en"
---

> Index of every page for AI agents: https://docs.superdurable.io/llms.txt

# Primitives

Primitives are the building blocks a Flow uses. Each one belongs to a Flow.

| Primitive                                                                  | What it is                                   | Use it to                                                        |
| -------------------------------------------------------------------------- | -------------------------------------------- | ---------------------------------------------------------------- |
| [Attribute](https://docs.superdurable.io/concepts/primitives/attribute.md) | Durable state that belongs to one Flow.      | Keep data between Steps, read it from outside, and search on it. |
| [RPC](https://docs.superdurable.io/concepts/primitives/rpc.md)             | A synchronous call into a Flow.              | Send commands and read views from your application.              |
| [Channel](https://docs.superdurable.io/concepts/primitives/channel.md)     | A durable message queue in a Flow.           | Deliver messages that Steps wait for.                            |
| [Stream](https://docs.superdurable.io/concepts/primitives/stream.md)       | A best-effort feed that a reader can resume. | Push live progress to a UI.                                      |
| [Timer](https://docs.superdurable.io/concepts/primitives/timer.md)         | A durable wait until a time.                 | Set deadlines, reminders, and schedules.                         |
| [SubFlow](https://docs.superdurable.io/concepts/primitives/subflow.md)     | A Flow that another Flow starts as a child.  | Split large or parallel work into child Flows.                   |

[Concepts](https://docs.superdurable.io/concepts.md) shows how the primitives fit with Flow, Step, Client, and Connector.