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‎pages/price-feeds/use-real-time-data/off-chain.mdx

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import { Tab, Tabs } from "nextra-theme-docs";
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# Off-chain Applications
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We provide SDKs in various programming languages that allow you to read the values of Pyth price feeds in off-chain applications, such as web frontends:
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<Tabs items={['JavaScript', 'Rust', 'Python', 'Go']}>
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<Tab>
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There are different javascript SDKs for different purposes.
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If you are developing an application that runs on any blockchain except Solana, then the javascript SDK for that blockchain supports querying and streaming live Pyth prices.
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You can find the code for this SDK in the [pyth-crosschain](https://github.com/pyth-network/pyth-crosschain) repository, under `target_chains/<chain name>/sdk/js`.
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These SDKs also support [pulling price updates](../pythnet-price-feeds/pull-updates) on to your target blockchain.
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An example for querying and streaming prices using these SDKs is shown [here](https://github.com/pyth-network/pyth-crosschain/tree/main/target_chains/ethereum/sdk/js#off-chain-prices).
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If you are developing an application for Solana, or without any blockchain whatsoever, then the [@pythnetwork/client](https://www.npmjs.com/package/@pythnetwork/client) npm package can be used to consume Pyth prices inside off-chain JavaScript programs.
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An example can be found [here](https://github.com/pyth-network/pyth-client-js#example-usage).
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</Tab>
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<Tab>
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The [pyth-sdk-solana crate](https://crates.io/crates/pyth-sdk-solana) can be used to consume Pyth prices inside your off-chain Rust programs. An example can be found [here](https://github.com/pyth-network/pyth-sdk-rs/blob/main/pyth-sdk-solana/examples/eth_price.rs).
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</Tab>
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<Tab>
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The [pyth-client-py](https://github.com/pyth-network/pyth-client-py) Python library can be used to consume Pyth prices inside your off-chain Python programs. An example can be found [here](https://github.com/pyth-network/pyth-client-py/blob/main/examples/read_one_price_feed.py).
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</Tab>
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<Tab>
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The [Blockdaemon pyth-go](https://github.com/Blockdaemon/pyth-go) client can be used to consume Pyth prices inside your off-chain Go programs.
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</Tab>
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</Tabs>
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You can find an in-depth explanation from one of our contributors, Daniel:
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[How to Build with Pyth Data Off-chain: Pyth Tutorials](https://youtu.be/YgD4IWTKD2c)
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# How to Use Real-Time Data in Off-Chain Applications
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This guide explains how to use the [typescript SDK client](https://github.com/pyth-network/pyth-crosschain/tree/main/price_service/client/js) to fetch the latest prices and subscribe to real-time price updates in off-chain applications.
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## Installation
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The Pyth SDK can be installed using npm or yarn.
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### npm
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```bash copy
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npm install --save @pythnetwork/price-service-client
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```
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### Yarn
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```bash copy
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yarn add @pythnetwork/price-service-client
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```
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## Usage
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Typical usage of the Pyth SDK involves creating a `PriceServiceConnection` instance, by passing the URL of the [Hermes](https://hermes.pyth.network/docs/#/) service to the constructor.
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You can then use the `getLatestPriceFeeds` method to fetch the latest prices of the specified price feeds.
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```typescript copy
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// Get the Stable Hermes service URL from https://docs.pyth.network/price-feeds/api-instances-and-providers/hermes
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const connection = new PriceServiceConnection("https://hermes.pyth.network");
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const priceIds = [
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"0xe62df6c8b4a85fe1a67db44dc12de5db330f7ac66b72dc658afedf0f4a415b43", // BTC/USD price id
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"0xff61491a931112ddf1bd8147cd1b641375f79f5825126d665480874634fd0ace", // ETH/USD price id
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];
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// Get the latest values of the price feeds as JSON objects.
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const currentPrices = await connection.getLatestPriceFeeds(priceIds);
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console.log(currentPrices);
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```
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The `getLatestPriceFeeds` method returns an array of `PriceFeed` objects. Each `PriceFeed` object contains the latest price, the Exponential Moving Average (EMA) price, and other metadata.
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```bash
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[
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PriceFeed {
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emaPrice: Price {
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conf: '3450227100',
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expo: -8,
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price: '6610104500000',
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publishTime: 1715870606
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},
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id: 'e62df6c8b4a85fe1a67db44dc12de5db330f7ac66b72dc658afedf0f4a415b43',
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metadata: undefined,
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vaa: undefined,
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price: Price {
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conf: '3315255511',
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expo: -8,
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price: '6619626406527',
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publishTime: 1715870606
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}
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},
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PriceFeed {
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emaPrice: Price {
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conf: '266713535',
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expo: -8,
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price: '297876550000',
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publishTime: 1715870606
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},
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id: 'ff61491a931112ddf1bd8147cd1b641375f79f5825126d665480874634fd0ace',
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metadata: undefined,
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vaa: undefined,
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price: Price {
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conf: '296893358',
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expo: -8,
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price: '296499502000',
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publishTime: 1715870606
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}
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}
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]
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```
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You can also subscribe to real-time price updates over a WebSocket connection using the `subscribePriceFeedUpdates` method.
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```typescript copy
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// priceIds here is the one declared in the above code snippet.
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const priceFeeds = await connection.getLatestPriceFeeds(priceIds);
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connection.subscribePriceFeedUpdates(priceIds, (priceFeed) => {
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// priceFeed here is the same as returned by getLatestPriceFeeds above.
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console.log(
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`Received an update for ${priceFeed.id}: ${priceFeed.getPriceNoOlderThan(
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60
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)}`
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);
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});
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// When using the subscription, make sure to close the WebSocket upon termination to finish the process gracefully.
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setTimeout(() => {
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connection.closeWebSocket();
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}, 60000);
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```
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## Additional Resources
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You may find these additional resources helpful.
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### Examples
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This [example](https://github.com/pyth-network/pyth-crosschain/blob/main/price_service/client/js/src/examples/PriceServiceClient.ts) demonstrates how to use the Pyth SDK to fetch prices.
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### Hermes API Reference
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The [Hermes API](https://hermes.pyth.network/docs/#/) reference lets you interactively explore the complete API of the Pyth Hermes service.
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### Price Feed IDs
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The [Price Feed Ids](https://pyth.network/developers/price-feed-ids) lists the price feeds available on the Pyth network.

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