SimpleX Chat is an open-source, decentralized messaging platform designed for privacy and security. Its core architectural principle is the complete absence of user identifiers, meaning it does not use phone numbers, usernames, or even random numbers to identify users on the network. This design aims to protect not only message content with end-to-end encryption but also metadata about who is communicating. ^{[1] [2]}​

Overview

SimpleX Chat was developed to provide a communication platform where users have full ownership and control over their identity, contacts, and data, free from centralized oversight. The project's mission is to offer a high degree of metadata protection, making it difficult for servers or network observers to determine the social graph of its users. Communications are routed through a decentralized network of SimpleX Messaging Protocol (SMP) servers, and users can host their own servers for greater autonomy. ^{[1] [3]}​

The platform operates on a custom-built protocol stack designed to minimize metadata exposure. Unlike conventional federated systems, SimpleX relays do not have a shared user address space, and each connection between users is isolated. While the project is supported by a for-profit company and has received venture capital funding, its developers have stated a long-term vision for protocol governance to be managed by non-profit entities to ensure its alignment with community interests. The project has been endorsed by privacy-focused organizations like Privacy Guides and Whonix and has gained public recognition from figures in the technology space, including Ethereum founder Vitalik Buterin. ^{[4] [5]}​

History

Development of SimpleX began around 2020. The first prototype of the SimpleX Messaging Server was announced in October 2020, followed by a terminal-based chat application in May 2021. The first public version of the mobile apps for iOS and Android, SimpleX Chat v1, was released in March 2022. ^{[6] [3]}​

Significant milestones in the platform's development include:

• July 2022 (v3.0): Introduction of end-to-end encrypted audio and video calls.
• August 2022 (v3.1): Added support for routing traffic through Tor via a SOCKS proxy and introduced secret chat groups.
• September 2022 (v3.2): Launched "Incognito Mode," allowing users to create a new random profile name for each new contact.
• November 2022 (v4.2): Published a security assessment conducted by the firm Trail of Bits.
• February 2023 (v4.5): Introduced multiple, separate chat profiles within a single app.
• March 2024 (v5.6): Implemented quantum-resistant encryption as a beta feature, using a hybrid post-quantum key exchange mechanism alongside the Double Ratchet algorithm.
• June 2024 (v5.8): Introduced Private Message Routing to hide user IP addresses from destination servers.
• August 2024 (v6.0): Announced an investment from Jack Dorsey and the firm Asymmetric. Private Message Routing became the default setting for all new connections.
• October 2024 (v6.1): Published a new cryptographic design review by Trail of Bits.
• December 2024 (v6.2): Announced a partnership with Flux to include Flux-operated servers in the app to enhance decentralization and privacy.
• July 2025 (v6.4.1): Introduced community protection features, such as the ability for group administrators to review new members before they can join.

The project's roadmap has included goals for 2025 to scale the network for large communities, with future plans to introduce "Community Vouchers" in 2026 to create a sustainable funding model for server operators. ^{[6] [1]}​

Architecture and Technology

SimpleX is built on a custom protocol stack designed specifically to operate without user identifiers and to minimize metadata leakage.

No User Identifiers

The foundational principle of SimpleX is the absence of any persistent, globally unique user IDs. Unlike other secure messengers that rely on phone numbers (Signal) or public key-based IDs (Session), SimpleX isolates every connection. A user's profile, contact list, and group memberships exist only on their local device. When connecting with a contact, the app creates a new, distinct set of identifiers for that specific relationship. This makes it computationally difficult for a network-level adversary to build a social graph of who is communicating with whom. ^{[4] [2]}​

Network and Protocols

The platform operates on a decentralized network of servers running its custom protocols.

SimpleX Messaging Protocol (SMP) and SimpleXMQ

SimpleX's network functionality is based on two key protocols:

• SimpleXMQ (SimpleX Message Queue): This is the low-level message queue protocol that defines how messages are passed through unidirectional (simplex) message queues. The reference implementation, also called SimpleXMQ, is written in Haskell and serves as the message broker for the network. ^[7]
• SMP (SimpleX Messaging Protocol): Built on top of SimpleXMQ, SMP is a client-server protocol that manages communication and the creation of message queues. A full bidirectional conversation between two users consists of two separate, unidirectional SMP queues—one for sending and one for receiving. ^[7]

SMP servers act as relays. They receive encrypted messages from a sender and place them in the correct anonymous queue, where they are later retrieved by the recipient. The server only sees a series of isolated message deliveries to opaque queue identifiers and cannot link the sender and receiver. Users can run their own SMP servers for maximum control and privacy. ^[2]​

Private Message Routing

To protect a user's IP address from their contact's server, SimpleX implements a system called Private Message Routing. Enabled by default since version 6.0, it uses a two-hop packet routing mechanism. A user's client encrypts the message for the destination server and then wraps it in another layer of encryption for a forwarding server. The forwarding server relays the packet to the destination server without knowing the final recipient's queue ID or the message content. This packet-based routing approach provides per-packet anonymity, preventing a destination server from linking multiple messages to the same user. ^[4]​

Encryption

SimpleX employs multiple layers of encryption to secure communications.

• End-to-End Encryption (E2EE): All one-to-one and group messages are E2E encrypted using the Signal Double Ratchet algorithm, which provides forward secrecy and post-compromise security.
• Post-Quantum Resistance: Since version 5.6, the platform incorporates a hybrid post-quantum key exchange using CRYSTALS-Kyber. This runs in parallel with the classic key exchange to protect conversations against future attacks from quantum computers.
• Transport Encryption: All communication between clients and servers is secured with TLS. ^[4]
• Local Encryption: The app also supports the encryption of the local chat database and media files stored on the user's device. ^[6]

File and Call Protocols

• SimpleX File Transfer Protocol (XFTP): For sending files, SimpleX uses a proprietary protocol designed to minimize metadata leakage. Files are temporarily stored on XFTP servers, and users can host their own.
• Voice and Video Calls: Calls are E2EE and use WebRTC technology. Users can configure their own STUN/TURN servers for routing calls, offering an additional layer of privacy. ^[2]

Features

SimpleX Chat is available on iOS, Android (via Google Play, F-Droid, and direct APK), Windows, macOS, and Linux. ^[1]​

• Communication: The app supports direct and secret group messaging, E2E encrypted audio/video calls, voice messages, message reactions, editing, and disappearing messages. ^[6]
• Profiles and Identity: Users can create multiple, isolated chat profiles within the app to separate different social contexts. An "Incognito Mode" generates a new random name for each new connection, further obscuring the user's main profile. ^[4]
• Connections: Users connect by sharing one-time invitation links or QR codes. Reusable SimpleX addresses can also be created for sharing publicly. ^[2]
• Message Delivery: The app uses a two-checkmark system to indicate message delivery: one check for delivery to the recipient's server queue and two checks for delivery to their device. The platform does not implement "read receipts," which the developers consider an "anti-feature" that creates social pressure. ^[4]
• Multi-Device Support: SimpleX does not support using the same profile seamlessly across multiple devices, as the developers view existing solutions as a security compromise. However, a mobile app can be linked to a desktop client on the same local network, which then acts as a remote for the mobile device. ^[4]
• Tor Integration: The app supports using Tor for network transport by configuring a SOCKS proxy (e.g., via Orbot). Tor is not bundled directly with the application. ^[4]

Funding and Business Model

SimpleX Chat is developed by a for-profit company, SimpleX Chat Ltd., and is funded through a combination of community donations and venture capital. In August 2024, the project announced an investment from Jack Dorsey and Asymmetric Capital Partners. The team has justified the use of VC funding as a practical necessity to compete with large, well-funded technology companies and to finance the research and development required. ^{[6] [4]}​

The project's long-term business model aims to fund development and network operations without compromising user privacy. The strategy includes a freemium model for the app, paid services for businesses, and a revenue-sharing system for server operators built around a utility token called Community Vouchers. ^{[4] [8]}​

Community Vouchers

Announced as a feature planned for 2026, Community Vouchers are a utility token system designed to create a sustainable and private funding model for the servers that power the SimpleX network's channels and groups. The system functions like a prepaid card, allowing community owners to pay for server capacity without compromising user privacy. ^[8]​

The core technology will be built on an EVM-based blockchain, such as an Ethereum L2 solution, and will use smart contracts to manage the system. To ensure privacy, the design incorporates zero-knowledge proofs (zk-proofs) to make the redemption of a voucher unlinkable to its original purchase on the public blockchain. Users will be able to purchase vouchers through standard in-app payment methods or with cryptocurrencies like Bitcoin (BTC) and Monero (XMR). ^[8]​

Key aspects of the economic model include:

• Non-Tradable Utility Tokens: Vouchers are designed as restricted utility tokens, not speculative investment assets. Smart contracts will prohibit or heavily restrict transfers. There will be no pre-mine or public sale.
• Fixed Pricing: The price of vouchers will be fixed based on server operating costs. The team has provided preliminary estimates of 10 per month for a community of 5,000 active users, with a free tier for smaller groups.
• Revenue Sharing: Funds from voucher sales are held in a smart contract escrow. Up to 60% of the revenue is released to server operators after they provide capacity, with the exact share determined by a trust evaluation based on uptime and operator history. The remaining funds are designated for network governance and development.
• Trustless Agreements: The use of smart contracts ensures that server operators are paid only after services are rendered, creating a trustless system for all parties. ^[8]

The system is currently in the design phase. SimpleX has released a free, non-transferrable NFT on the Ethereum mainnet that grants early access to the test version of the vouchers. ^[8]​

Security, Privacy, and Advocacy

Privacy and security are central to the SimpleX project. The platform has undergone and published multiple third-party security audits by the firm Trail of Bits in 2022 and 2024. In April 2024, the project published legally binding Transparency Reports, affirming its commitment to its privacy claims. ^{[6] [1]}​

SimpleX Chat is a vocal advocate for digital privacy. In November 2025, the project took a strong stance against the EU's "Chat Control" legislation, arguing that its true purpose was to enable mass surveillance for training AI models. This advocacy aligns with endorsements the project has received from prominent figures in the privacy space. On November 26, 2025, Ethereum founder Vitalik Buterin mentioned SimpleX as one of two messaging apps "pushing forward" important next steps for privacy, specifically "permissionless account creation" and "metadata privacy." ^[5]​

Team

• Evgeny Poberezkin: The founder of SimpleX Chat. He is a software developer known for creating Ajv, a widely used JavaScript library for data validation. ^[3]