# ECHO

> The typed, local-first object graph. Objects are stored on the device as CRDT documents and merged between peers.

## Start here

- [Welcome](https://dxos.org/docs/echo/welcome.md): What ECHO is and how these docs are organized.
- [Why ECHO?](https://dxos.org/docs/echo/why-echo.md): Why apps and agents share one data model: agent memory, introspection, external data, then the argument for a typed, local-first object graph.

## Learning path

- [The ECHO object](https://dxos.org/docs/echo/learn/the-echo-object.md): What a live object is, and the app the learning path builds, running.
- [Installation](https://dxos.org/docs/echo/learn/installation.md): Add the packages and open a database in Node or the browser.
- [Defining types](https://dxos.org/docs/echo/learn/defining-types.md): Declare the tutorial app's types, with references between them, and see the form ECHO derives from each.
- [Mutating objects](https://dxos.org/docs/echo/learn/mutating-objects.md): Create, change and remove the tutorial app's records, and observe each change.
- [Querying](https://dxos.org/docs/echo/learn/querying.md): Select the tutorial app's records with Filter and Query, by type, sorted, searched, and live.
- [Sharing a space](https://dxos.org/docs/echo/learn/sharing.md): Invite a second peer to the tutorial app's space and watch both replicas follow each other's edits.

## Core concepts

- [Spaces and databases](https://dxos.org/docs/echo/concepts/spaces.md): The unit of sharing, access and replication.
- [Objects and relations](https://dxos.org/docs/echo/concepts/objects-relations.md): Entities, the reserved fields, and parent and child ownership.

## Guides

- [React](https://dxos.org/docs/echo/guides/react.md): The tutorial app's React layer: ClientProvider, useQuery, useObject and a schema form, and the reactivity rules behind them.

## Reference

- [Filter](https://dxos.org/docs/echo/reference/filter.md): Predicate builders that compile to a query AST.