> Source: https://docs.logos.co/messaging
> Markdown index of all Logos docs: https://docs.logos.co/llms.txt

# Introduction to Logos Messaging

#### Learn how Logos can be used to build private, censorship-resistant communication applications.

> **Info**
>
> This document reflects the state of this Logos component as it will exist on mainnet. Some features described here may not be available on the current testnet.

[Logos Messaging](https://docs.logos.co/get-started/glossary.md#logos-messaging) is the messaging layer of the Logos technology stack. It lets applications send messages, relay data, and coordinate with one another without relying on centralised servers or exposing metadata. It uses a peer-to-peer relay network where messages propagate across nodes with no central broker, supporting private one-to-one messaging, group messaging, and public broadcast channels.

## The basics

- Logos Messaging comprises two [modules](https://docs.logos.co/get-started/glossary.md#module): [Delivery](https://github.com/logos-messaging/logos-delivery), a peer-to-peer [transport](https://docs.logos.co/get-started/glossary.md#transport) layer with spam protection, and [Chat](https://github.com/logos-messaging/logos-chat), a library for private, end-to-end encrypted conversations built on top of Delivery.
- Messages propagate across a peer-to-peer relay network with no central broker. Anyone can run a node and there is no gas fee for sending or receiving messages.
- Delivery is modular. Applications combine a set of protocols—[Relay](https://docs.logos.co/messaging/concepts/protocols.md#relay), [RLN Relay](https://docs.logos.co/messaging/concepts/protocols.md#rln-relay), [Filter](https://docs.logos.co/messaging/concepts/protocols.md#filter), [Store](https://docs.logos.co/messaging/concepts/protocols.md#store), and [Light Push](https://docs.logos.co/messaging/concepts/protocols.md#light-push)—to balance anonymity, scalability, and latency for their own use case.
- Logos Messaging is built on top of [libp2p](https://docs.logos.co/messaging/concepts/logos-delivery-and-libp2p.md), but adds a service network that anyone can use without deploying their own infrastructure, along with economic spam protection that libp2p does not provide.

## Architecture

Logos Messaging is implemented as two modules that sit on top of the Logos networking layer: [Delivery](https://github.com/logos-messaging/logos-delivery), which handles peer-to-peer transport, and [Chat](https://github.com/logos-messaging/logos-chat), which builds private conversations on top of it.

### Delivery

Delivery is the peer-to-peer messaging network at the base of the messaging stack, and the reference implementation of the Logos Messaging protocol. It provides publish-subscribe messaging over an open, censorship-resistant network with no central broker, and it protects the network from spam using [RLN](https://docs.logos.co/messaging/get-started/faq.md#what-are-rate-limiting-nullifiers-rln), which verifies a zero-knowledge proof rather than a publisher's identity.

Delivery's functionality is split across a set of [protocols](https://docs.logos.co/messaging/concepts/protocols.md):

- **Relay** extends [libp2p GossipSub](https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/README.md) to provide the base publish/subscribe messaging that peers use to send and receive messages.
- **RLN Relay** extends Relay with rate limiting nullifiers for economic, privacy-preserving spam prevention.
- **Filter** lets [light nodes](https://docs.logos.co/get-started/glossary.md#light-node) selectively subscribe to messages by content topic, trading some privacy for lower bandwidth use.
- **Store** temporarily retains messages so offline peers can retrieve what they missed, though it does not guarantee availability—applications that need durable storage should pair Delivery with [Logos Storage](https://docs.logos.co/get-started/glossary.md#logos-storage) instead.
- **Light Push** lets bandwidth-constrained nodes publish a message and receive an acknowledgement that at least one peer received it, without guaranteeing network-wide propagation.

These protocols interact across three [network domains](https://docs.logos.co/messaging/concepts/network-domains.md): the discovery domain, where nodes locate other peers; the gossip domain, where Relay and RLN Relay distribute messages; and the request/response domain, where Store, Filter, and Light Push serve resource-limited nodes directly.

Messages are routed using [content topics](https://docs.logos.co/messaging/concepts/content-topics.md), developer-set metadata strings that let protocols filter, route, and retrieve messages.. How narrowly or broadly an application scopes its content topics is a direct privacy trade-off: Filter, Store, and Light Push all disclose content topics to peers, so grouping many users under shared topics increases k-anonymity, while splitting traffic into topic "buckets" helps distribute load for high-traffic applications.

Delivery is [transport-agnostic](https://docs.logos.co/messaging/concepts/transports.md), so developers choose the protocol that fits their environment: TCP by default for service nodes, and secure WebSocket for browsers, with WebRTC, WebTransport, and QUIC under research for future support.

To join the network, a node [bootstraps](https://docs.logos.co/get-started/glossary.md#bootstrapping) using one of several [peer discovery](https://docs.logos.co/messaging/concepts/understand-peer-discovery/peer-discovery.md) mechanisms—including static peers, [DNS discovery](https://docs.logos.co/get-started/glossary.md#dns-discovery), Discv5, and [Peer Exchange](https://docs.logos.co/get-started/glossary.md#peer-exchange)—and then keeps looking for peers to maintain a healthy Relay mesh, reserve backup connections, and find peers with specific capabilities such as Store or Filter.

### Chat

Chat is a protocol and library that provides one-to-one and group conversations with end-to-end encryption, using de-MLS for group messaging. It uses Delivery as its transport, so applications get everything they need to add private chat without designing and securing their own messaging protocol from scratch.

### Security features

Logos Messaging's [security guarantees](https://docs.logos.co/messaging/concepts/security-features.md) vary by protocol and are documented openly in the underlying RFCs. Relay provides pseudonymity and unlinkability between publishers, subscribers, and their activity, backed by [GossipSub](https://docs.logos.co/get-started/glossary.md#gossipsub)'s peer-scoring mechanism and ongoing RLN research for spam protection. Data confidentiality, integrity, and authenticity are available through the [Waku](https://docs.logos.co/get-started/glossary.md#waku) Message format and Noise protocols. Protocols that require a direct connection, such as Store and Filter, trade away some of that unlinkability, since a node can associate a peer's `PeerID` with the topics or filters it queries.

### Logos Messaging and libp2p

Logos Messaging is [built on top of libp2p](https://docs.logos.co/messaging/concepts/logos-delivery-and-libp2p.md) and shares much of its terminology, but it goes further in two ways. Developers can use it without deploying their own infrastructure, though anyone can choose to run a node to help decentralise the network. It is also a turnkey solution for privacy-preserving, censorship-resistant, platform-agnostic messaging, including out-of-the-box support for offline and resource-limited devices through Store, Filter, and Light Push, plus economic spam protection through RLN Relay, which libp2p does not provide on its own.