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In this guide we’ll build a nodejs application that listens for price changes on a token in realtime. We’ll show how to do it two ways, one with webhooks and another with subscriptions.

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Webhooks

Install the Codex SDK 
npm install @codex-data/sdk
Create a new file called index.js and add the following code: 
const { Codex } = require('@codex-data/sdk');

const client = new Codex(process.env.CODEX_API_KEY);
Now we have to add the token address and network id to code so we can start listening for price changes. 
const watchTokenAddress = '0xbb4cdb9cbd36b01bd1cbaebf2de08d9173bc095c';
const networkId = 56;
Next, we’ll need be able to receive webhook deliveries on our local computer. Let’s use loophole to do this. https://loophole.cloud/download After getting that setup and seeing your loophole url, copy it and save it for later. Now lets make the request to make a webook subscription, replacing the value for the host 
const hook = await client.mutation(`
  mutation CreateWebhooks {
    createWebhooks(
      input: {priceWebhooksInput: {webhooks: [{alertRecurrence: INDEFINITE, callbackUrl: "<my loophole url>", name: "uniswap", securityToken: "dasdsfds", groupId: "test-group", conditions: {tokenAddress: {eq: "0x5a98fcbea516cf06857215779fd812ca3bef1b32"}, networkId: {eq: 1}, priceUsd: {gt: "0"}}}]}}
    ) {
      priceWebhooks {
        alertRecurrence
        callbackUrl
        created
        id
        name
        webhookType
        groupId
        status
        conditions {
          ... on PriceEventWebhookCondition {
            __typename
            networkId {
              eq
            }
            priceUsd {
              eq
              gt
              gte
              lt
              lte
            }
            tokenAddress {
              eq
            }
          }
        }
      }
    }
  }
`)

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Subscriptions