Substrate Connect

Blockchain User Interfaces are still Centralized

The communication between a standard user interface (UI) and a network node is through a JSON RPC protocol. Generally, the UI will showcase the information that is available on the node, and this is done through two main approaches:

  1. User-Controlled Nodes: The UI connects to a node client that the user has installed on their machine.

    • These nodes are secure, but installation and maintenance of these nodes tend to be an inconvenience.

  2. Publicly-Accessible Nodes: The UI connects to a third-party-owned publicly-accessible node client.

    • While these nodes are more prevalent in their usage as they are convenient to use, they are centralized and insecure.

There is now a new paradigm: instead of specifying a centralized RPC node, developers just need to define the blockchain's chain specification for their application to synchronize with the chain. This is possible with Substrate connect.

What is Substrate Connect?

Replacing RPC node reliance with light clients

Substrate connect is a JavaScript library and browser extension that builds on the PolkadotJS API) to enable developers to build application-specific light clients for Substrate chains. There is no installation required or optional extension with minimal or no maintenance. The node is run by the JavaScript engine.

Simply put, Substrate connect is a Substrate client that runs in JavaScript.

Application developers no longer need to rely on single RPC nodes to allow end-users to interact with their applications.

Substrate (full node) vs. Substrate connect (light client)

A light client is a client that lets you utilize all the possibilities of the chain, but it does not require you to run a full copy of the entire blockchain.

Substrate: Full nodeSubstrate connect: Light client

full verification of all blocks of the chain

only verifies the authenticity of blocks of the chain

holds all of the previous block data and the chain's storage in database

no database

installation, maintenance, and execution tend to be exhaustive and require system administration expertise.

no installation; has an optional extension with minimal or no maintenance. Initializes in five to ten seconds

How to use Substrate Connect

As a JavaScript library

Substrate connect provides a PolkadotJS API connected to a bundled node. Through the use of the library, a user can run an actual Substrate-compatible node.

A node bundled with its user interface: ready-to-use light clients

The UI connects to a node client that is directly integrated: convenient, secure, and decentralized. This is accomplished through Substrate connect using a smoldot Wasm light client to securely connect to the blockchain network without relying on specific third parties.

Application developers can now run a Substrate light client in any NodeJS environment (@substrate/connect). Currently, Substrate connect supports Polkadot, Kusama, Westend, and Rococo; because light clients are part of the overall Substrate framework, they are available for Substrate-based blockchains.

As a browser extension

Establishing a sufficient number of peers is difficult due to browser limitations on WebSockets from HTTPS pages, as many nodes need to be available with TLS. The browser extension provided by Substrate connect helps to overcome this limitation and keeps the chains synced in the background, allowing applications to run faster.

Bundling light-clients of multiple chains

The browser extension allows end-users to interact with applications connected to multiple blockchains or connect their own blockchains to applications that support it.


Substrate Connect will auto-detect whether a user is using the extension. If not, the Wasm light client will be created in-page for them.


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