# ECHO

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

## Start here

- [Overview](https://dxos.org/docs/echo/overview.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.
- [Build with a coding agent](https://dxos.org/docs/echo/build-with-a-coding-agent.md): Have Claude Code, Codex or Cursor build a small ECHO app, from a prompt the reader can edit first.

## 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.
- [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.
- [Mutating objects](https://dxos.org/docs/echo/learn/mutating-objects.md): Create, change and remove the tutorial app's records, and observe each change.
- [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

- [Types and schema](https://dxos.org/docs/echo/concepts/types.md): What a type is, how ECHO identifies it, and how it changes over time.
- [Objects and relations](https://dxos.org/docs/echo/concepts/objects-relations.md): Typed records in one space, and the entities that join them.
- [References and DXNs](https://dxos.org/docs/echo/concepts/references.md): How objects point at each other, and how a reference resolves.
- [Feeds](https://dxos.org/docs/echo/concepts/feeds.md): An append log of ECHO objects, as a tree of branches.
- [Queries](https://dxos.org/docs/echo/concepts/queries.md): Filters, query shapes, traversal and live results.
- [Spaces and databases](https://dxos.org/docs/echo/concepts/spaces.md): The unit of sharing and replication, how it is stored, and the Hypergraph over all of them.
- [Changes and branches](https://dxos.org/docs/echo/concepts/changes.md): Every write as a change, how changes merge, history, and branches of objects.

## Guides

- [Effect](https://dxos.org/docs/echo/guides/effect.md): Use ECHO from Effect code: `Database.Service`, layers and typed errors.
- [Testing](https://dxos.org/docs/echo/guides/testing.md): Test code that uses ECHO, with isolated peers.
- [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.
- [Configuration](https://dxos.org/docs/echo/guides/configuration.md): Load a client's config from files and environment variables instead of writing it in code.

## API

- [Type](https://dxos.org/docs/echo/api/type.md): Declare and inspect object and relation types, and convert them to and from JSON Schema.
- [Annotation](https://dxos.org/docs/echo/api/annotation.md): The annotations tools read from a type.
- [Obj](https://dxos.org/docs/echo/api/obj.md): The runtime API for objects, their changes and the Entity helpers they share with relations.
- [Relation](https://dxos.org/docs/echo/api/relation.md): The runtime API for relations.
- [Ref](https://dxos.org/docs/echo/api/ref.md): Typed references between entities.
- [Database](https://dxos.org/docs/echo/api/database.md): The database of one space, and the Hypergraph over every space.
- [Query](https://dxos.org/docs/echo/api/query.md): Graph-shaped selections, traversal, ordering, aggregates, sources and results.
- [Filter](https://dxos.org/docs/echo/api/filter.md): Predicate builders that compile to a query AST.
- [Feed](https://dxos.org/docs/echo/api/feed.md): The append-only feed object.
- [Text](https://dxos.org/docs/echo/api/text.md): Collaborative text fields.
- [Blob](https://dxos.org/docs/echo/api/blob.md): Binary data stored beside objects.

## Resources

- [llms.txt](https://dxos.org/docs/echo/resources/llms-txt.md): The ECHO site map and full text for agents, in the llms.txt format.