> ## Documentation Index > Fetch the complete documentation index at: https://sequence-0fb8d9e6-api_docs.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Webhooks Webhooks are a feature that allows systems to be called upon across the internet based on the emission of a blockchain event that meets some criteria. You can listen to transactions via webhooks using the Sequence Indexer by registering an endpoint or removing it after it's no longer required. If you prefer a no-code way to add webhooks that uses the Sequence Builder, check out [this walkthrough](/solutions/builder/webhooks). To begin, direct yourself to the [Sequence Builder](https://sequence.build) and follow [this walkthrough for Public API Access Key](/solutions/builder/getting-started#claim-an-api-access-key) and [this walkthrough for a Secret API Access Key](/solutions/builder/getting-started#4-optional-for-development-create-a-service-account), both required for using the Sequence Indexer Webhooks. Function 1. [Register a Webhook Listener](/api-references/indexer/examples/webhook-listener#1-register-a-webhook-listener) 2. [Remove a Webhook Listener](/api-references/indexer/examples/webhook-listener#2-remove-a-webhook-listener) Webhook Response * [Webhook Listener Response](/api-references/indexer/examples/webhook-listener#webhook-listener-response) Example * [Listen to All Mints & Transfers of a specific ERC1155 TokenID](/api-references/indexer/examples/webhook-listener#listen-to-a-specific-token-id-for-an-erc1155) If you require a server for development, you can use the following: [Template Nodejs Webhook Server](https://github.com/0xsequence-demos/template-nodejs-webhook-server/blob/master/README.md) combined with [ngrok](https://ngrok.com) a secure tunnel to your computer running the local server ## 1. Register a Webhook Listener Our filters allow you to listen to on-chain events for particular contract addresses, contract events, specific token ids, account addresses, or topic hashes. If you require a webhook endpoint to call, you can use [webhook.site](https://webhook.site/) for testing purposes to specify used in the `url` field. *Sequence Indexer `AddWebhookListener` Method:* with `required*` fields * Request: POST /rpc/Indexer/AddWebhookListener * Content-Type: application/json * Body (in JSON): * `url*` (string) -- the URL to send the webhook to * `filters*` (object) -- an object of filters * `contractAddresses*` (\[]string) -- an array of any contract address * `events*` (\[]string)-- any contract event, with the included `indexed` keyword from the contract when necessary (e.g. `Transfer(address indexed from, address indexed to, uint256 amount)`. Shorthand is also acceptable without argument names, which will simply be parsed as: arg1, arg2, etc. i.e. `Transfer(address indexed,address indexed,uint256)` without argument names) * `tokenIDs` (\[]int) -- an array of token IDs * `accounts` (\[]string) -- an array of wallet addresses to listen on * `topicHashes` (\[]string) -- a hash of the event being listened to (e.g. ethers.id("Transfer(address indexed from, address indexed to, uint256 amount)"))
For a full list of events from the various token types: ERC20, ERC721, or ERC1155, [view here](/api-references/indexer/examples/webhook-listener#on-chain-token-event-types). **Example: `AddWebhookListener`** Where this example listens to all mints of an ERC1155 collectible contract: ```bash cURL theme={null} curl -X POST \ -H "Content-Type: application/json" \ -H "X-Access-Key: " \ -H "Authorization: BEARER " \ -d '{ "url": "", "filters": { "contractAddresses": ["0x9bec34c1f7098e278afd48fedcf13355b854364a"], "events": ["TransferSingle(address indexed operator, address indexed from, address indexed to, uint256 id, uint256 value)"], } }' \ https://arbitrum-sepolia-indexer.sequence.app/rpc/Indexer/AddWebhookListener ``` ```typescript TypeScript theme={null} // Works in both a Webapp (browser) or Node.js: import { SequenceIndexer } from '@0xsequence/indexer' const indexer = new SequenceIndexer('https://polygon-indexer.sequence.app', '', '') const req = { url: 'https://webhook.site/27c266b7-ee69-4046-8319-75ce91ec2bcf', filters: { contractAddresses: ['0x631998e91476DA5B870D741192fc5Cbc55F5a52E'], events: ["TransferSingle(address indexed operator, address indexed from, address indexed to, uint256 id, uint256 value)"] } } const ok = await indexer.addWebhookListener({ Url: req.url, Filters: req.filters }) console.log('ok', ok) ``` ```go Go theme={null} import ( "context" "fmt" "log" "net/http" "github.com/0xsequence/go-sequence/indexer" ) func GetTransactionHistory(accountAddress string) { seqIndexer := indexer.NewIndexer("https://polygon-indexer.sequence.app", '', '') ok, err := seqIndexer.AddWebhookListener(context.Background(), &proto.WebhookListener{ Url: "https://webhook.site/27c266b7-ee69-4046-8319-75ce91ec2bcf", Filters: &proto.WebhookEventFilter{ Accounts: []prototyp.Hash{prototyp.HashFromString("0xd4Bbf5d234CC95441A8Af0a317D8874eE425e74d")}, ContractAddresses: []prototyp.Hash{prototyp.HashFromString("0xC852bf35CB7B54a33844B181e6fD163387D85868")}, // TokenIDs: []prototyp.BigInt{prototyp.NewBigInt(1)}, }, }, ) fmt.Println(ok, err) } ``` ## 2. Remove a Webhook Listener If you need to clean up your webhook listeners, you can submit requests to remove the listener based on listener `id` and `projectId`: *Sequence Indexer `RemoveWebhookListener` Method:* with `required*` fields * Request: POST /rpc/Indexer/RemoveWebhookListener * Content-Type: application/json * Body (in JSON): * `id*` (string) -- the id of the listener returned from `AddWebhookListener` (i.e. `response.listener.id`) * `projectId*` (string) -- the Project ID the JWT Secret API key was obtained from **Example: `RemoveWebhookListener`** ```bash cURL theme={null} curl -X POST \ -H "Content-Type: application/json" \ -H "X-Access-Key: " \ -H "Authorization: BEARER " \ -d '{ "id": , "projectId": }' \ https://arbitrum-sepolia-indexer.sequence.app/rpc/Indexer/RemoveWebhookListener ``` ```typescript TypeScript theme={null} // Works in both a Webapp (browser) or Node.js: import { SequenceIndexer } from '@0xsequence/indexer' const indexer = new SequenceIndexer('https://arbitrum-sepolia-indexer.sequence.app', '', '') const ok = await indexer.removeWebhookListener({ id: , projectId: }) console.log('ok', ok) ``` ```go Go theme={null} import ( "context" "fmt" "log" "net/http" "github.com/0xsequence/go-sequence/indexer" ) func RemoveWebhook(accountAddress string) { seqIndexer := indexer.NewIndexer("https://polygon-indexer.sequence.app", '', ) ok, err := seqIndexer.RemoveWebhookListener(context.Background(), &proto.WebhookListener{ id: , projectId: , }, ) fmt.Println(ok, err) } ``` ## Webhook Listener Response Upon webhook listener response, an object is returned in the following structure * Response (in JSON): * `uid` (string) -- a deterministic hash value of the on-chain transaction log * `type` (string), -- the type of event (i.e. `BLOCK_ADDED`) * `blockNumber` (i32) -- the block number from the blockchain for when the event occured * `blockHash` (string) -- the hash of the block for the transaction * `parentBlockHash` (i32) -- the hash of the parent block * `contractAddress` (string) -- the contract address from where the event came from * `contractType` (string) -- the type of contract (e.g. `ERC20`, `ERC721`, `ERC1155`, etc.) * `txnHash` (string) -- the transaction hash of the event * `txnIndex` (i32) -- the index of the transaction in the blockchain block * `txnLogIndex` (string) -- the log index in the transaction * `ts` (date) -- an ISO 8601 formatted date and time of the event * `event` ([event](/api-references/indexer/examples/webhook-listener#event-object)) -- the event data of the on-chain data * `txnLogIndex` (string) -- the log index in the transaction * `logDataType` (string) -- the type of log event (e.g. `TOKEN_TRANSFER`) * `rawLog` ([raw](/api-references/indexer/examples/webhook-listener#rawlog-object)) -- the raw transaction object ## Example ### Listen to a Specific Token ID for an ERC1155 If you want to get all mints and transfers of a specific token ID for an ERC1155 ```bash cURL theme={null} curl -X POST \ -H "Content-Type: application/json" \ -H "X-Access-Key: " \ -H "Authorization: BEARER " \ -d '{ "url": "", "filters": { "contractAddresses": ["0x9bec34c1f7098e278afd48fedcf13355b854364a"], "events": ["TransferSingle(address indexed operator, address indexed from, address indexed to, uint256 id, uint256 value)"], "tokenIDs": ["1237"] } }' \ https://arbitrum-sepolia-indexer.sequence.app/rpc/Indexer/AddWebhookListener ``` ```typescript TypeScript theme={null} // Works in both a Webapp (browser) or Node.js: import { SequenceIndexer } from '@0xsequence/indexer' const indexer = new SequenceIndexer( 'https://arbitrum-sepolia-indexer.sequence.app', '', ' ### On-chain Token Event Types #### ERC20 * Transfer(address indexed from, address indexed to, uint256 value) * Approval(address indexed owner, address indexed spender, uint256 value) #### ERC721 * Transfer(address indexed from, address indexed to, uint256 indexed tokenId) * Approval(address indexed owner, address indexed approved, uint256 indexed tokenId) * ApprovalForAll(address indexed owner, address indexed operator, bool approved) #### ERC1155 * TransferSingle(address indexed operator, address indexed from, address indexed to, uint256 id, uint256 value) * TransferBatch(address indexed operator, address indexed from, address indexed to, uint256\[] ids, uint256\[] values) * ApprovalForAll(address indexed account, address indexed operator, bool approved) * URI(string value, uint256 indexed id) ### Custom Return Data Types Glossary ##### event (object) | Field | Type | Description | | --------- | --------- | ---------------------------------------------------------------------------------------------------------------------------------------------------- | | topicHash | string | a hash of the event being listened to (e.g. ethers.id("Transfer(address indexed from, address indexed to, uint256 amount)")) | | eventSig | string | the event signature of the on-chain event (e.g. "Transfer(address indexed from, address indexed to, uint256 amount)") | | types | \[]string | an array of argument types from the event | | names | \[]string | an array of event argument names in plain text (note: if names are not included in initial webhook creation, will appear as: arg1, arg2, arg3, etc.) | | values | \[]string | an array of hex values corresponding to the argument names | ##### rawLog (object) | Field | Type | Description | | ------ | --------- | ------------------------------------------ | | data | string | data | | topics | \[]string | the topic event hashes emitted in the logs |