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+---
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+title: Create your first Pyth app on EVM
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+description: Build and test an EVM app using Pyth price feeds
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+slug: /price-feeds/core/create-your-first-pyth-app/evm/part-1
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+---
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+
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+import { Step, Steps } from "fumadocs-ui/components/steps";
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+
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+In this tutorial, we will use real-time Pyth price data to mint an NFT in exchange for $1 of ETH.
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+Our solidity contract will read the price of ETH/USD from Pyth and use it to calculate the amount of ETH required to mint the NFT.
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+
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+This tutorial will cover the following topics:
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+
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+- Create a contract that reads the ETH/USD price from Pyth using [pyth-sdk-solidity](https://github.com/pyth-network/pyth-crosschain/tree/main/target_chains/ethereum/sdk/solidity)
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+- Learn how to update Pyth prices to avoid Stale data.
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+- Deploy the contract to OP-sepolia testnet.
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+- Update and Fetch price using [hermes-client](https://github.com/pyth-network/pyth-crosschain/tree/main/apps/hermes/client/js).
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+
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+This tutorial is divided into two parts:
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+
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+- [Part 1:](./part-1) Create a contract and fetch prices from Pyth oracles. \
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+- [Part 2:](.//part-2) Deploy Your Pyth App
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+
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+## Create a contract and fetch prices from Pyth oracles
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+
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+In this part of the tutorial, we will create a contract that reads the price from Pyth and uses it to calculate the amount of ETH required to mint an NFT.
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+After that, we will write tests to ensure that the contract works as expected.
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+
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+### Preliminaries
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+
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+This tutorial uses Foundry to perform the contract development tasks.
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+Please make sure these are installed on your system before continuing.
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+
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+- [foundry](https://book.getfoundry.sh/getting-started/installation)
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+- [node](https://nodejs.org/en/download/)
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+- [curl](https://curl.se/download.html)
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+- [jq](https://stedolan.github.io/jq/download/)
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+
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+<Steps>
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+<Step>
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+
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+### Create a Foundry project
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+
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+Create a new directory to hold your app and a `contracts` directory within.
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+Here `forge init` command will initialize an empty foundry project creating several subdirectories within `contracts`.
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+
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+```bash copy
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+mkdir my_first_pyth_app
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+mkdir my_first_pyth_app/contracts && cd my_first_pyth_app/contracts
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+forge init
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+```
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+
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+The `src` directory will hold your contract code, and the `test` directory will hold unit tests.
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+Both directories are initialized with some sample contract code and tests.
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+
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+Try it out by running `forge test`.
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+This command should print out something like this:
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+
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+```
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+[⠢] Compiling...
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+No files changed, compilation skipped
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+
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+Running 2 tests for test/Counter.t.sol:CounterTest
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+[PASS] testFuzz_SetNumber(uint256) (runs: 256, μ: 27864, ~: 28409)
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+[PASS] test_Increment() (gas: 28379)
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+Test result: ok. 2 passed; 0 failed; 0 skipped; finished in 12.30ms
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+
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+Ran 1 test suites: 2 tests passed, 0 failed, 0 skipped (2 total tests)
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+```
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+
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+The Foundry project has been successfully initialized!
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+At this point, delete the sample code from `src` and the test file from `test` -- we won't need them anymore.
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+
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+```bash copy
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+rm -r src/* test/* scripts/*
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+```
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+
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+</Step>
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+
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+<Step>
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+
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+### Install the Pyth SDK
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+
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+Pyth provides a Solidity SDK that can be used to interact with one-chain Pyth Price Feed contracts.
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+It exposes multiple [methods](/price-feeds/core/api-reference) to read and interact with the contracts.
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+
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+Use `npm` to add the Pyth SDK:
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+
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+```bash copy
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+npm init -y
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+npm install @pythnetwork/pyth-sdk-solidity
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+```
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+
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+Next, run the following command to create a text file `contracts/remappings.txt`:
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+
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+```bash copy
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+echo '@pythnetwork/pyth-sdk-solidity/=node_modules/@pythnetwork/pyth-sdk-solidity' > remappings.txt
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+```
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+
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+This line tells Foundry where to find the Pyth SDK so that you can import it from Solidity contracts.
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+
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+</Step>
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+
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+<Step>
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+
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+### Create a contract
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+
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+Next, open `src/MyFirstPythContract.sol` in your favorite editor and add the following code:
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+
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+```solidity copy filename="MyFirstPythContract.sol"
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+// SPDX-License-Identifier: UNLICENSED
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+pragma solidity ^0.8.13;
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+
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+import { console2 } from "forge-std/Test.sol";
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+import "@pythnetwork/pyth-sdk-solidity/IPyth.sol";
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+
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+contract MyFirstPythContract {
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+ IPyth pyth;
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+ bytes32 ethUsdPriceId;
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+
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+ constructor(address _pyth, bytes32 _ethUsdPriceId) {
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+ pyth = IPyth(_pyth);
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+ ethUsdPriceId = _ethUsdPriceId;
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+ }
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+}
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+
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+```
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+
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+Notice that this code block imports the `IPyth` interface from the SDK you installed earlier.
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+This interface is the primary way to interact with the Pyth price feeds contract.
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+The constructor instantiates this interface with the address of the Pyth contract.
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+It also takes an `_ethUsdPriceId`.
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+We will see how to populate both parameters later on.
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+
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+Next, add a `mint` function to your contract:
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+
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+```solidity copy filename="MyFirstPythContract.sol"
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+contract MyFirstPythContract {
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+ // ... other functions omitted
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+
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+ function mint() public payable {
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+ PythStructs.Price memory price = pyth.getPriceNoOlderThan(
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+ ethUsdPriceId,
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+ 60
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+ );
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+
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+ uint ethPrice18Decimals = (uint(uint64(price.price)) * (10 ** 18)) /
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+ (10 ** uint8(uint32(-1 * price.expo)));
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+ uint oneDollarInWei = ((10 ** 18) * (10 ** 18)) / ethPrice18Decimals;
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+
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+ console2.log("required payment in wei");
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+ console2.log(oneDollarInWei);
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+
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+ if (msg.value >= oneDollarInWei) {
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+ // User paid enough money.
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+ // TODO: mint the NFT here
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+ } else {
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+ revert InsufficientFee();
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+ }
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+ }
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+
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+ // Error raised if the payment is not sufficient
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+ error InsufficientFee();
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+}
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+
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+```
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+
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+This function first reads a `Price` from the pyth contract if it is updated within the last 60 seconds.
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+It then performs some arithmetic on the price in order to calculate how much the caller needs to pay. This conversion
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+assumes that 10^18 wei is equal to the native token (ETH in this example); in some networks (like Hedera) the decimal
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+places are different and you need to change the math.
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+If the caller has not paid enough, the function reverts.
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+
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+Try out your changes by running `forge build`:
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+
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+```
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+[⠒] Compiling...
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+[⠘] Compiling 28 files with 0.8.23
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+[⠊] Solc 0.8.23 finished in 2.71s
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+Compiler run successful!
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+```
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+
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+The contract compiles!
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+
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+</Step>
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+
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+<Step>
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+
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+### Create a test
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+
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+Before deploying the contract, let's write a test to make sure it works.
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+Open `test/MyFirstPythContract.t.sol` in your favorite editor and add the following code:
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+
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+```solidity copy filename="MyFirstPythContract.t.sol"
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+// SPDX-License-Identifier: UNLICENSED
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+pragma solidity ^0.8.13;
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+
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+import { Test, console2 } from "forge-std/Test.sol";
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+import { MyFirstPythContract } from "../src/MyFirstPythContract.sol";
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+import { MockPyth } from "@pythnetwork/pyth-sdk-solidity/MockPyth.sol";
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+
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+contract MyFirstPythContractTest is Test {
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+ MockPyth public pyth;
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+ bytes32 ETH_PRICE_FEED_ID = bytes32(uint256(0x1));
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+ MyFirstPythContract public app;
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+
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+ uint256 ETH_TO_WEI = 10 ** 18;
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+
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+ function setUp() public {
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+ pyth = new MockPyth(60, 1);
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+ app = new MyFirstPythContract(address(pyth), ETH_PRICE_FEED_ID);
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+ }
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+
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+ function createEthUpdate(
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+ int64 ethPrice
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+ ) private view returns (bytes[] memory) {
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+ bytes[] memory updateData = new bytes[](1);
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+ updateData[0] = pyth.createPriceFeedUpdateData(
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+ ETH_PRICE_FEED_ID,
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+ ethPrice * 100000, // price
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+ 10 * 100000, // confidence
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+ -5, // exponent
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+ ethPrice * 100000, // emaPrice
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+ 10 * 100000, // emaConfidence
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+ uint64(block.timestamp), // publishTime
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+ uint64(block.timestamp) // prevPublishTime
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+ );
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+
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+ return updateData;
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+ }
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+
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+ function setEthPrice(int64 ethPrice) private {
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+ bytes[] memory updateData = createEthUpdate(ethPrice);
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+ uint value = pyth.getUpdateFee(updateData);
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+ vm.deal(address(this), value);
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+ pyth.updatePriceFeeds{ value: value }(updateData);
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+ }
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+
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+ function testMint() public {
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+ setEthPrice(100);
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+
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+ vm.deal(address(this), ETH_TO_WEI);
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+ app.mint{ value: ETH_TO_WEI / 100 }();
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+ }
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+
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+ function testMintRevert() public {
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+ setEthPrice(99);
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+
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+ vm.deal(address(this), ETH_TO_WEI);
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+ vm.expectRevert();
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+ app.mint{ value: ETH_TO_WEI / 100 }();
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+ }
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+}
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+
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+```
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+
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+Take a look at the two `test` functions at the end of this file.
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+These tests set the price of Ether to a specific value, then call `mint`.
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+The tests use a mock implementation of Pyth and some helper methods defined above to set the price of Ether.
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+
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+Try your tests by running `forge test -vvv`
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+
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+```
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+[⠢] Compiling...
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+[⠔] Compiling 1 files with 0.8.23
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+[⠒] Solc 0.8.23 finished in 1.23s
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+Compiler run successful!
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+
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+Running 2 tests for test/MyFirstPythContract.t.sol:MyFirstPythContractTest
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+[PASS] testMint() (gas: 197064)
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+Logs:
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+ required payment in wei
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+ 10000000000000000
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+
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+[PASS] testMintRevert() (gas: 197468)
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+Logs:
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+ required payment in wei
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+ 10101010101010101
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+
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+Test result: ok. 2 passed; 0 failed; 0 skipped; finished in 702.58µs
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+
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+Ran 1 test suites: 2 tests passed, 0 failed, 0 skipped (2 total tests)
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+```
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+
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+The tests pass!
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+The tests also print out the required payment to successfully mint the NFT -- these originate from the `console2.log` statements in `MyFirstPythContract`.
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+Notice that the payment is higher in the second test: when the price of ETH is \$99 (instead of \$100), more ETH is required to reach \$1.
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+This difference demonstrates that your contract is successfully reading the price of ETH/USD from Pyth.
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+
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+</Step>
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+
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+<Step>
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+
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+### Update Pyth prices
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+
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+While our code above seems to work properly, it has a problem.
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+To see this problem, let's add another test to the test suite:
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+
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+```solidity copy filename="MyFirstPythContract.t.sol"
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+contract MyFirstPythContractTest is Test {
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+ // ... prior tests omitted ...
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+
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+ function testMintStalePrice() public {
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+ setEthPrice(100);
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+
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+ skip(120);
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+
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+ vm.deal(address(this), ETH_TO_WEI);
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+ app.mint{ value: ETH_TO_WEI / 100 }();
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+ }
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+}
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+
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+```
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+
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+Notice that this test is the same as the first test, except it adds a call to [`skip`](https://book.getfoundry.sh/reference/forge-std/skip) in the middle.
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+
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+Now run `forge test -vvv`
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+
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+```
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+[FAIL. Reason: StalePrice()] testMintStalePrice() (gas: 192722)
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+```
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+
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+Oh no, the test fails with a `StalePrice` error!
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+When our contract calls `getPriceNoOlderThan(.., 60)`, it checks the timestamp on the blockchain and compares it to the timestamp for the Pyth price.
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+If the Pyth price's timestamp is more than 60 seconds in the past, then a `StalePrice` error occurs.
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+`skip` moves the timestamp on the blockchain forward, which triggers the error.
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+
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+We can fix this problem, but first, let's fix the test case.
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+Add a call to `vm.expectRevert()` as shown below:
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+
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+```solidity {10} copy filename="MyFirstPythContract.t.sol "
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+contract MyFirstPythContractTest is Test {
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+ // ... prior tests omitted ...
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+ function testMintStalePrice() public {
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+ setEthPrice(100);
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+
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+ skip(120);
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+
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+ vm.deal(address(this), ETH_TO_WEI);
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+ // Add this line
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+ vm.expectRevert();
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+ app.mint{ value: ETH_TO_WEI / 100 }();
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+ }
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+}
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+
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+```
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+
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+To fix the `StalePrice` error, add a new function to `MyFirstPythContract`:
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+
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+```solidity copy filename="MyFirstPythContract.sol"
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+contract MyFirstPythContract {
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+ // ... prior code omitted
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+
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+ function updateAndMint(bytes[] calldata pythPriceUpdate) external payable {
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+ uint updateFee = pyth.getUpdateFee(pythPriceUpdate);
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+ pyth.updatePriceFeeds{ value: updateFee }(pythPriceUpdate);
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+
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+ mint();
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+ }
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+}
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+
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+```
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+
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+The end of this function calls the `mint` function we defined before.
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+Before that, however, the function calls [`updatePriceFeeds`](https://api-reference.pyth.network/price-feeds/evm/updatePriceFeeds) on the Pyth contract.
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+This function takes a payload of `bytes[]` that is passed into the function itself.
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+The Pyth contract requires a fee to perform this update; the code snippet above calculates the needed fee using [`getUpdateFee`](https://api-reference.pyth.network/price-feeds/evm/getUpdateFee).
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+The caller of this function can pass in a recent Pyth price update as this payload, guaranteeing that the `StalePrice` error won't occur.
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+
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+We can test this function by adding the following snippet to the test file:
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+
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+```solidity copy filename="MyFirstPythContract.t.sol"
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+contract MyFirstPythContractTest is Test {
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+ // ... prior tests omitted ...
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+ function testUpdateAndMint() public {
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+ bytes[] memory updateData = createEthUpdate(100);
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+
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+ vm.deal(address(this), ETH_TO_WEI);
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+ app.updateAndMint{ value: ETH_TO_WEI / 100 }(updateData);
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+ }
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+}
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+
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+```
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+
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+Note that this test creates and passes a price update directly to `updateAndMint` instead of calling `setEthPrice` like
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+the previous tests. For this test, we created a mock price update using the testing library.
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+When the contract is deployed, we will retrieve the price update from a web service.
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+
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+Run this new test with `forge test -vvv`
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+
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+```
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+[⠢] Compiling...
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+[⠰] Compiling 1 files with 0.8.23
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+[⠔] Solc 0.8.23 finished in 1.19s
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+Compiler run successful!
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+
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+Running 4 tests for test/MyFirstPythContract.t.sol:MyFirstPythContractTest
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+[PASS] testMint() (gas: 197148)
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|
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+Logs:
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|
|
+ required payment in wei
|
|
|
+ 10000000000000000
|
|
|
+
|
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+[PASS] testMintRevert() (gas: 197575)
|
|
|
+Logs:
|
|
|
+ required payment in wei
|
|
|
+ 10101010101010101
|
|
|
+
|
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+[PASS] testMintStalePrice() (gas: 193074)
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|
|
+[PASS] testUpdateAndMint() (gas: 197067)
|
|
|
+Logs:
|
|
|
+ required payment in wei
|
|
|
+ 10000000000000000
|
|
|
+
|
|
|
+Test result: ok. 4 passed; 0 failed; 0 skipped; finished in 1.54ms
|
|
|
+
|
|
|
+Ran 1 test suites: 4 tests passed, 0 failed, 0 skipped (4 total tests)
|
|
|
+```
|
|
|
+
|
|
|
+The test passes!
|
|
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+
|
|
|
+Congratulations! We have successfully created a contract that reads the price of ETH/USD from Pyth and uses it to calculate the amount of ETH required to mint an NFT.
|
|
|
+
|
|
|
+In this part of the tutorial, we learned how to create a contract that reads the price from Pyth oracle and how to update the price to avoid stale data.
|
|
|
+We also wrote tests to ensure that the contract works as expected.
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|
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+
|
|
|
+Our final contract code should look like this:
|
|
|
+
|
|
|
+```solidity copy filename="MyFirstPythContract.sol"
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|
|
+// SPDX-License-Identifier: UNLICENSED
|
|
|
+pragma solidity ^0.8.13;
|
|
|
+
|
|
|
+import { console2 } from "forge-std/Test.sol";
|
|
|
+import "@pythnetwork/pyth-sdk-solidity/IPyth.sol";
|
|
|
+
|
|
|
+contract MyFirstPythContract {
|
|
|
+ IPyth pyth;
|
|
|
+ bytes32 ethUsdPriceId;
|
|
|
+
|
|
|
+ constructor(address _pyth, bytes32 _ethUsdPriceId) {
|
|
|
+ pyth = IPyth(_pyth);
|
|
|
+ ethUsdPriceId = _ethUsdPriceId;
|
|
|
+ }
|
|
|
+
|
|
|
+ function mint() public payable {
|
|
|
+ PythStructs.Price memory price = pyth.getPriceNoOlderThan(
|
|
|
+ ethUsdPriceId,
|
|
|
+ 60
|
|
|
+ );
|
|
|
+ console2.log("price of ETH in USD");
|
|
|
+ console2.log(price.price);
|
|
|
+
|
|
|
+ uint ethPrice18Decimals = (uint(uint64(price.price)) * (10 ** 18)) /
|
|
|
+ (10 ** uint8(uint32(-1 * price.expo)));
|
|
|
+ uint oneDollarInWei = ((10 ** 18) * (10 ** 18)) / ethPrice18Decimals;
|
|
|
+
|
|
|
+ console2.log("required payment in wei");
|
|
|
+ console2.log(oneDollarInWei);
|
|
|
+
|
|
|
+ if (msg.value >= oneDollarInWei) {
|
|
|
+ // User paid enough money.
|
|
|
+ // TODO: mint the NFT here
|
|
|
+ } else {
|
|
|
+ revert InsufficientFee();
|
|
|
+ }
|
|
|
+ }
|
|
|
+
|
|
|
+ function updateAndMint(bytes[] calldata pythPriceUpdate) external payable {
|
|
|
+ uint updateFee = pyth.getUpdateFee(pythPriceUpdate);
|
|
|
+ pyth.updatePriceFeeds{ value: updateFee }(pythPriceUpdate);
|
|
|
+
|
|
|
+ mint();
|
|
|
+ }
|
|
|
+
|
|
|
+ // Error raised if the payment is not sufficient
|
|
|
+ error InsufficientFee();
|
|
|
+}
|
|
|
+
|
|
|
+```
|
|
|
+
|
|
|
+And our test file should look like this:
|
|
|
+
|
|
|
+```solidity copy filename="MyFirstPythContract.t.sol"
|
|
|
+// SPDX-License-Identifier: UNLICENSED
|
|
|
+pragma solidity ^0.8.13;
|
|
|
+
|
|
|
+import { Test, console2 } from "forge-std/Test.sol";
|
|
|
+import { MyFirstPythContract } from "../src/MyFirstPythContract.sol";
|
|
|
+import { MockPyth } from "@pythnetwork/pyth-sdk-solidity/MockPyth.sol";
|
|
|
+
|
|
|
+contract MyFirstPythContractTest is Test {
|
|
|
+ MockPyth public pyth;
|
|
|
+ bytes32 ETH_PRICE_FEED_ID = bytes32(uint256(0x1));
|
|
|
+ MyFirstPythContract public app;
|
|
|
+
|
|
|
+ uint256 ETH_TO_WEI = 10 ** 18;
|
|
|
+
|
|
|
+ function setUp() public {
|
|
|
+ pyth = new MockPyth(60, 1);
|
|
|
+ app = new MyFirstPythContract(address(pyth), ETH_PRICE_FEED_ID);
|
|
|
+ }
|
|
|
+
|
|
|
+ function createEthUpdate(
|
|
|
+ int64 ethPrice
|
|
|
+ ) private view returns (bytes[] memory) {
|
|
|
+ bytes[] memory updateData = new bytes[](1);
|
|
|
+ updateData[0] = pyth.createPriceFeedUpdateData(
|
|
|
+ ETH_PRICE_FEED_ID,
|
|
|
+ ethPrice * 100000,
|
|
|
+ 10 * 100000,
|
|
|
+ -5,
|
|
|
+ ethPrice * 100000,
|
|
|
+ 10 * 100000,
|
|
|
+ uint64(block.timestamp),
|
|
|
+ uint64(block.timestamp)
|
|
|
+ );
|
|
|
+
|
|
|
+ return updateData;
|
|
|
+ }
|
|
|
+
|
|
|
+ function setEthPrice(int64 ethPrice) private {
|
|
|
+ bytes[] memory updateData = createEthUpdate(ethPrice);
|
|
|
+ uint value = pyth.getUpdateFee(updateData);
|
|
|
+ console2.log("value: ", value);
|
|
|
+ vm.deal(address(this), value);
|
|
|
+ pyth.updatePriceFeeds{ value: value }(updateData);
|
|
|
+ }
|
|
|
+
|
|
|
+ function testMint() public {
|
|
|
+ setEthPrice(100);
|
|
|
+
|
|
|
+ vm.deal(address(this), ETH_TO_WEI);
|
|
|
+ app.mint{ value: ETH_TO_WEI / 100 }();
|
|
|
+ }
|
|
|
+
|
|
|
+ function testMintRevert() public {
|
|
|
+ setEthPrice(99);
|
|
|
+
|
|
|
+ vm.deal(address(this), ETH_TO_WEI);
|
|
|
+ vm.expectRevert();
|
|
|
+ app.mint{ value: ETH_TO_WEI / 100 }();
|
|
|
+ }
|
|
|
+
|
|
|
+ function testMintStalePrice() public {
|
|
|
+ setEthPrice(100);
|
|
|
+
|
|
|
+ skip(120);
|
|
|
+
|
|
|
+ vm.deal(address(this), ETH_TO_WEI);
|
|
|
+
|
|
|
+ vm.expectRevert();
|
|
|
+ app.mint{ value: ETH_TO_WEI / 100 }();
|
|
|
+ }
|
|
|
+
|
|
|
+ function testUpdateAndMint() public {
|
|
|
+ bytes[] memory updateData = createEthUpdate(100);
|
|
|
+
|
|
|
+ vm.deal(address(this), ETH_TO_WEI);
|
|
|
+ app.updateAndMint{ value: ETH_TO_WEI / 100 }(updateData);
|
|
|
+ }
|
|
|
+}
|
|
|
+
|
|
|
+```
|
|
|
+
|
|
|
+</Step>
|
|
|
+
|
|
|
+</Steps>
|
|
|
+
|
|
|
+Check out [Part 2](./part-2.mdx) to learn how to deploy our contract to OP-sepolia testnet and fetch prices using hermes-client.
|
Aditya Arora