light client draft

Author: CrackTheCode016

develop/light-clients.md

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+---
+title: Light Clients
+description: Learn about Polkadot light clients: their importance, usage, and how they enable robust, cohesive, and secure application composition.
+template: root-subdirectory-page.html
+---
+
+Polkadot has first class support for light clients, which are a crucial part of the development of decentralized applications on Polkadot.
+
+Light clients are a more secure, trust-minimized, efficient way of communicating to a blockchain.  Along with the oft-used JSON remote procedural calls (RPC), they are one of the primary methods for interacting with a blockchain. 
+
+However, unlike interacting with a JSON RPC interface, where an application has to either maintain a list of providers to use, or rely on a single node, **light clients are not limited to nor depend on a single node**. They verify the state of the blockchain using cryptographic proofs, ensuring it has not only the latest but *correct* state. As it just verifies the headers of the blocks, it has no need to download the whole state, making it ideal for resource-constrained environments.
+
+## JSON RPC and Light Client Comparison
+
+Another common mode of communication between a user interface (UI) and a node is through a JSON RPC
+protocol. Generally, the UI will showcase the information that is available on the node, fetch information related to the network and/or its [pallets](../polkadot-protocol/glossary.md#pallet), and overall interact with the network. 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.
+
+| Full Node                                                                                        | Light Client                                                                               |
+| ----------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------- |
+| Full verification of all blocks of the chain                                                                | Only verifies the authenticity of blocks of the chain                                                         |
+| Contains 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; is typically included as part of the application |
+
+## Using Light Clients
+
+[`smoldot`](https://github.com/smol-dot/smoldot){target=\blank} is the cornerstone for light client implementation and usage for Polkadot SDK-based chains. It contains the primitives needed to build clients, or is included in libraries such as [PAPI](#papi-light-client-support).
+
+### PAPI Light Client Support
+
+The [Polkadot API (PAPI)](./toolkit/api-libraries/papi.md){target=\blank} provides native support for a light client configuration (backed by [`smoldot`](https://github.com/smol-dot/smoldot){target=\blank}), allowing a developer to use a light client to connect to multiple chains at the same time. 
+
+<!-- TODO: Add reference to a PAPI tutorial here -->
+
+### Substrate Connect - Browser Extension
+
+The [Substrate Connect browser extension](https://www.npmjs.com/package/@substrate/connect-extension-protocol){target=\blank} allows end-users to interact with applications connected to multiple blockchains or connect their own blockchains to applications that support it.
+
+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.
+
+!!!note
+    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.
+
+## Resources
+
+- [What is a light client and why you should care?](https://www.parity.io/blog/what-is-a-light-client/){target=\blank}
+- [Introducing Substrate Connect: Browser-Based Light Clients for Connecting to Substrate Chains](https://www.parity.io/blog/introducing-substrate-connect){target=\blank}
+- [Substrate connect GitHub Repo](https://github.com/paritytech/substrate-connect/tree/master/projects/extension){target=\blank}
+- [7. Light Clients - Polkadot Specification](https://spec.polkadot.network/sect-lightclient){target=\blank}