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Heystack chat app


This example application demonstrates important features of the Stacks blockchain, and is a case study for how a frontend web application can interact with a Clarity smart contract. The full source of the application is provided and completely open source for you to use or modify. This page highlights important code snippets and design patterns to help you learn how to develop your own Stacks application.

This app showcases the following platform features:

  • Authenticating users with the web wallet
  • Using a smart contract to store data on the blockchain
  • Minting new fungible tokens with a SIP-010 compliant smart contract
  • Creating and monitoring transactions on the Stacks blockchain using Stacks.js

You can access the online version of the Heystack app to interact with it. The source for Heystack is also available on Github. This page assumes some familiarity with React.

Heystack overview#

Heystack is a web application for chatting with other Stacks users. The application uses the Stacks web wallet to authenticate users in the frontend. When a user logs in to Heystack, they're given a genesis amount of $HEY fungible tokens, which allows them to send and like messages on the platform.

Heystack is powered by Clarity smart contracts so each message is a transaction on the Stacks blockchain. Each time a user sends a message on the platform, they must sign the message with the Stacks web wallet (or another compatible wallet) and pay a small gas fee in STX. A user spends a $HEY token to send every message, and recieves a $HEY token for every like that their messages receive.

The following video provides a brief overview of the Heystack application:

Review smart contracts#

Heystack depends on two smart contracts to execute the backend functions of the app on the Stacks blockchain:

  • a contract for handling the messaging content
  • a contract for minting and distributing the $HEY token

As a best practice, these two contracts are separate because of the different functionality they handle. This is an exercise in separation of concerns.

Content contract#

The hey.clar contract provides two primary functions for the application, one to publish content to the blockchain and another to like a piece of content based on its ID. This section reviews the implementation of these primary functions, but is not a comprehensive discussion of the contract.

In order to accomplish the two primary functions, the contract relies on a data variable content-index and two data maps, like-state and publisher-state which contain the number of likes a piece of content has received, and the principal address of the account that published the content.

Note that all variables are defined at the top of the contract, which is a requirement of the Clarity language. These include constants such as the contract-creator, error codes, and a treasury address.

;;;; Data maps and vars(define-data-var content-index uint u0)
(define-read-only (get-content-index)  (ok (var-get content-index)))
(define-map like-state  { content-index: uint }  { likes: uint })
(define-map publisher-state  { content-index: uint }  { publisher: principal })

Read-only functions provide a method for getting the like count of a piece of content, and getting the principal address of the message publisher.

(define-read-only (get-like-count (id uint))  ;; Checks map for like count of given id  ;; defaults to 0 likes if no entry found  (ok (default-to { likes: u0 } (map-get? like-state { content-index: id }))))
(define-read-only (get-message-publisher (id uint))  ;; Checks map for like count of given id  ;; defaults to 0 likes if no entry found  (ok (unwrap-panic (get publisher (map-get? publisher-state { content-index: id }))))

The get-like-count method accepts a content ID and returns the number of likes associated with that content. The method uses the default-to function to return 0 if the content ID isn't found in the map of likes.

The get-message-publisher method accepts a content ID and returns the principal address of the content publisher. The method uses the unwrap-panic function to halt execution of the method if the principal address isn't found in the map of publishers.

The two primary public methods are the send-message and like-message functions. These methods allow the contract caller to store a message on the blockchain (creating entries in the data maps for the message sender and the number of likes). Note that the message itself isn't stored in a contract variable, the frontend application reads the content of the message directly from the transaction on the blockchain.

;;;; Public functions(define-public (send-message (content (string-utf8 140)))  (let ((id (unwrap! (increment-content-index) (err u0))))    (print { content: content, publisher: tx-sender, index: id })    (map-set like-state      { content-index: id }      { likes: u0 }    )    (map-set publisher-state      { content-index: id }      { publisher: tx-sender }    )    (transfer-hey u1 HEY_TREASURY)  ))

The send-message method accepts a utf-8 string with a maximum length of 140 characters. The method defines an internal variable id using the let function and assigns the next content ID to that variable by calling the increment-contract-index method of the contract. The value assignment of this variable is bound by the unwrap! function, which returns an error and exits the control-flow if the increment-contract-index function isn't successfully called.

The method then assigns u0 likes to the content in the like-state data map, and adds the principal address to the publisher-state data map using the map-set function. Finally, the private method transfer-hey is called to transfer 1 $HEY token from the message sender to the $HEY treasury address stored in the HEY_TREASURY constant.

(define-public (like-message (id uint))  (begin    ;; cannot like content that doesn't exist    (asserts! (>= (var-get content-index) id) (err ERR_CANNOT_LIKE_NON_EXISTENT_CONTENT))    ;; transfer 1 HEY to the principal that created the content    (map-set like-state      { content-index: id }      { likes: (+ u1 (get likes (unwrap! (get-like-count id) (err u0)))) }    )    (transfer-hey u1 (unwrap-panic (get-message-publisher id)))  ))

The like-message method accepts a content ID. The method checks that the ID is lower than the current content ID using the asserts! function, to verify that the provided ID is a valid ID. If the asserts! assessment is false, the method returns an error code. If the ID is valid, the method performs a map-set to look up the content in the like-state data map and add a like to the value stored in the map. Once again, the unwrap! function is used to ensure that an invalid value isn't stored in the map.

The hey.clar contract provides some additional functions for working with the $HEY token contract, discussed in the next section.

Token contract#

Heystack creates a native fungible token for use in the application. When a user authenticates with Heystack, they're automatically eligible to claim 100 $HEY tokens to allow them to start messaging.

SIP-010 defines the fungible token standard on Stacks, which allows Stacks compatible wallets to handle fungible tokens through a set of standardized methods. SIP-010 defines 7 traits that a fungible token contract must have in order to be compliant:

  • transfer: method for transferring the token from one principal to another
  • get-name: returns the human-readable name of the token
  • get-symbol: returns the ticker symbol of the token
  • get-decimals: returns number of decimal places in the token
  • get-balance: return the balance of a given principal
  • get-total-supply: returns the total supply of the token
  • get-token-uri: returns an optional string that resolves to a valid URI for the token's metadata.

In Clarity, a contract can declare that it intends to implement a set of standard traits.

;; Implement the `ft-trait` trait defined in the `ft-trait` contract;; 'ST3J2GVMMM2R07ZFBJDWTYEYAR8FZH5WKDTFJ9AHA.ft-trait.sip-010-trait)

The impl-trait function asserts that the smart contract is fully implementing a given set of traits defined by the argument. Like variable definitions, impl-trait must be declared at the top of a smart contract definition.


The contract address for SIP-010 trait definition is different depending on which network (mainnet, testnet, etc.) your contract is deployed on. See the standard for the current addresses of the standard traits.

The hey-token.clar contract implements the required 7 traits of SIP-010, and one additional method, the gift-tokens method, that allows a principal to request tokens from the contract.

(define-public (gift-tokens (recipient principal))  (begin    (asserts! (is-eq tx-sender recipient) (err u0))    (ft-mint? hey-token u1 recipient)  ))


Authentication is handled through the @stacks/connect-react and @stacks/auth packages, which interact with compatible Stacks wallet extensions and provide methods for interacting with a user session respectively. Jotai provides application state management.

The connect wallet button component implements the interface with the Stacks web wallet through the @stacks/connect-react package.

import { Button } from "@components/button";import React from "react";import { useConnect } from "@stacks/connect-react";import { ButtonProps } from "@stacks/ui";import { useLoading } from "@hooks/use-loading";import { LOADING_KEYS } from "@store/ui";
export const ConnectWalletButton: React.FC<ButtonProps> = (props) => {  const { doOpenAuth } = useConnect();  const { isLoading, setIsLoading } = useLoading(LOADING_KEYS.AUTH);  return (    <Button      isLoading={isLoading}      onClick={() => {        void setIsLoading(true);        doOpenAuth();      }}      {...props}    >      Connect wallet    </Button>  );};

Once connected, /src/store/auth.ts populates the user session data into the Jotai store, allowing the application to access the user information.

You can see in the welcome panel component how the presence or absence of stored user data is used to display the wallet connect button or the signed in view.

...const UserSection = memo((props: StackProps) => {  const { user } = useUser();
  return (    <Stack      alignItems="center"      justifyContent="center"      flexGrow={1}      spacing="loose"      textAlign="center"      {...props}    >      {!user ? <SignedOutView /> : <SignedInView onClick={() => console.log('click')} />}    </Stack>  );});...

Token faucet#

The use-claim-hey.ts file provides a React hook for interacting with the token faucet of the Clarity smart contract.

import { useLoading } from "@hooks/use-loading";import { LOADING_KEYS } from "@store/ui";import { useConnect } from "@stacks/connect-react";import { useNetwork } from "@hooks/use-network";import { useCallback } from "react";import { useHeyContract } from "@hooks/use-hey-contract";import { REQUEST_FUNCTION } from "@common/constants";import { principalCV } from "@stacks/transactions/dist/clarity/types/principalCV";import { useCurrentAddress } from "@hooks/use-current-address";
export function useHandleClaimHey() {  const address = useCurrentAddress();  const { setIsLoading } = useLoading(LOADING_KEYS.CLAIM_HEY);  const { doContractCall } = useConnect();  const [contractAddress, contractName] = useHeyContract();  const network = useNetwork();
  const onFinish = useCallback(() => {    void setIsLoading(false);  }, [setIsLoading]);
  const onCancel = useCallback(() => {    void setIsLoading(false);  }, [setIsLoading]);
  return useCallback(() => {    void setIsLoading(true);    void doContractCall({      contractAddress,      contractName,      functionName: REQUEST_FUNCTION,      functionArgs: [principalCV(address)],      onFinish,      onCancel,      network,      stxAddress: address,    });  }, [setIsLoading, onFinish, network, onCancel, address, doContractCall]);}

The @stacks/connect-react package exports the doContractCall method, which interacts with the smart contract on the blockchain. There are more examples of transaction calls in the next section. It's important to note that it's necessary to convert Javascript types to Clarity types using the types exported by the @stacks/transactions package. Further discussion of this conversion is in the Clarity types in Javascript section.


Since messages in Heystack are transactions against a Clarity smart contract, the application must be able to create transactions and read their content from the blockchain. The following sections highlight code snippets that perform Clarity transactions and read both completed and pending transactions from the Stacks blockchain.

Issuing transactions#

The two primary functions of the hey.clar smart contract are publishing a message and accepting a like on an already published message. The [src/hooks/use-publish-hey.ts][] file implements the frontend method for calling the smart contract on the blockchain with the appropriate values.

...  return useCallback(    (content: string, _onFinish: () => void) => {      void setShowPendingOverlay(true);      void setIsLoading(true);
      void doContractCall({        contractAddress,        contractName,        functionName: MESSAGE_FUNCTION,        functionArgs: [          stringUtf8CV(content),          attachmentUri !== '' ? someCV(stringUtf8CV(attachmentUri)) : noneCV(),        ],        onFinish: () => {          _onFinish();          onFinish();        },        postConditions: [          createFungiblePostCondition(            address,            FungibleConditionCode.Equal,            new BN(1),            createAssetInfo(contractAddress, 'hey-token', 'hey-token')          ),        ],        onCancel,        network,        stxAddress: address,      });    },    [setIsLoading, onFinish, network, onCancel, address, doContractCall]  );...

The frontend uses the doContractCall function from the @stacks/connect-react package to perform the call to the Clarity smart contract. In order to support the mapping of Javascript types to Clarity types, helpers exported from the @stacks/transactions package are used as arguments to the contract call.

Note that the contract call also create post conditions to verify that a single $HEY token is transferred by the execution of the contract call. Post conditions are a powerful feature of Clarity that can be used to prevent rug-pulling and other detrimental behavior by smart contracts.

Reading transactions#

Heystack achieves pseudo-real-time messaging by reading both confirmed and pending transactions from the blockchain. Pending transactions are read from the mempool, whereas confirmed transactions are read directly from the chain. The src/store/hey.ts file contains the implementation of both.

...export const heyTransactionsAtom = atomWithQuery<ContractCallTransaction[], string>(get => ({  queryKey: ['hey-txs'],  ...(defaultOptions as any),  refetchInterval: 500,  queryFn: async (): Promise<ContractCallTransaction[]> => {    const client = get(accountsClientAtom);    const txClient = get(transactionsClientAtom);
    const txs = await client.getAccountTransactions({      limit: 50,      principal: HEY_CONTRACT,    });    const txids = (txs as TransactionResults).results      .filter(        tx =>          tx.tx_type === 'contract_call' &&          tx.contract_call.function_name === MESSAGE_FUNCTION &&          tx.tx_status === 'success'      )      .map(tx => tx.tx_id);
    const final = await Promise.all( txId => txClient.getTransactionById({ txId })));    return final as ContractCallTransaction[];  },}));...

The getAccountTransactions from the AccountsApi object exported by @stacks/blockchain-api-client is used to read confirmed blockchain transactions against the hey.clar contract from the Stacks API. The list of transactions returned by the API is filtered to only transactions representing a call to the message function that was successful, and then mapped to an array of transaction IDs.

Finally, the array of IDs is used to read each full transaction from the blockchain using the getTransactionsById method from the TransactionsApi object exported by the @stacks/blockchain-api-client package.

Pending transactions are read from the mempool in a similar implementation.

export const pendingTxsAtom = atomWithQuery<Heystack[], string>((get) => ({  queryKey: ["hey-pending-txs"],  refetchInterval: 1000,  ...(defaultOptions as any),  queryFn: async (): Promise<Heystack[]> => {    const client = get(transactionsClientAtom);
    const txs = await client.getMempoolTransactionList({ limit: 96 });    const heyTxs = (txs as MempoolTransactionListResponse).results      .filter(        (tx) =>          tx.tx_type === "contract_call" &&          tx.contract_call.contract_id === HEY_CONTRACT &&          tx.contract_call.function_name === MESSAGE_FUNCTION &&          tx.tx_status === "pending"      )      .map((tx) => tx.tx_id);
    const final = await Promise.all( (txId) => client.getTransactionById({ txId }))    );
    return (      (final as ContractCallTransaction[]).map((tx) => {        const attachment = tx.contract_call.function_args?.[1].repr          .replace(`(some u"`, "")          .slice(0, -1);
        return {          sender: tx.sender_address,          content: tx.contract_call.function_args?.[0].repr            .replace(`u"`, "")            .slice(0, -1) as string,          id: tx.tx_id,          attachment: attachment === "non" ? undefined : attachment,          timestamp: (tx as any).receipt_time,          isPending: true,        };      }) || []    );  },}));

Pending transactions are read from the mempool using the getMempoolTransactionList method from the TransactionsApi exported by @stacks/blockchain-api-client. Similar to confirmed transactions, the returned array is filtered to a list of IDs, and then used to generate an array of full transactions.

Because of differences in the data structure of the pending transactions vs. confirmed transactions, the pending transaction list must be standardized before being returned.

Note that for the low stakes of a messaging app, pending transactions can be treated as likely permanent state transitions. For applications implementing higher stakes business logic (such as the transfer of representations of value) it would be more appropriate to wait to display confirmed transactions.

Clarity types in Javascript#

In order to create transactions to call functions in Clarity contracts, the @stacks/transactions package exports classes that make it easy to construct well-typed Clarity values in Javascript. According to the Clarity language specification, Clarity has the following types:

  • (tuple (key-name-0 key-type 0) (key-name-1 key-type-1) ...) - a typed tuple with named fields
  • (list max-len entry-type) - a list of maximum length max-len, with entries of type entry-type
  • (response ok-type err-type) - object used by public functions to commit their state changes or abort
  • (optional some-type) - an option type for objects that can be either (some-value) or none
  • (buff max-len) - byte buffer of maximum length
  • principal - object representing a principal address (contract or standard)
  • bool - boolean value (true or false)
  • int - signed 128-bit integer
  • uint - unsigned 128-bit integer

To support these types in Javascript, @stacks/transactions exports the following helpers:

// construct boolean clarity valuesconst t = trueCV();const f = falseCV();
// construct optional clarity valuesconst nothing = noneCV();const something = someCV(t);
// construct a buffer clarity value from an existing Bufferconst buffer = Buffer.from("foo");const bufCV = bufferCV(buffer);
// construct signed and unsigned integer clarity valuesconst i = intCV(-10);const u = uintCV(10);
// construct principal clarity valuesconst address = "SP2JXKMSH007NPYAQHKJPQMAQYAD90NQGTVJVQ02B";const contractName = "contract-name";const spCV = standardPrincipalCV(address);const cpCV = contractPrincipalCV(address, contractName);
// construct response clarity valuesconst errCV = responseErrorCV(trueCV());const okCV = responseOkCV(falseCV());
// construct tuple clarity valuesconst tupCV = tupleCV({  a: intCV(1),  b: trueCV(),  c: falseCV(),});
// construct list clarity valuesconst l = listCV([trueCV(), falseCV()]);

You should use these helpers when calling Clarity contracts with Javascript to avoid failed contract calls due to bad typing.

Reading BNS names#

An important feature of Stacks is the Blockchain Naming System (BNS). BNS allows users to register a human-readable identity to their account, that can act as both a username and a web address.

Names registered to a user can be read from a Stacks API endpoint, as demonstrated in src/store/names.ts.


Due to ecosystem limitations, it's currently uncommon for BNS names to be registered on any testnet. For the purpose of demonstration, Heystack looks for BNS names against the user's mainnet wallet address.

export const namesAtom = atomFamily((address: string) =>  atom(async (get) => {    if (!address || address === "") return;    const network = get(mainnetNetworkAtom);    if (!network) return null;
    const local = getLocalNames(network.coreApiUrl, address);
    if (local) {      const [names, timestamp] = local;      const now =;      const isStale = now - timestamp > STALE_TIME;      if (!isStale) return names;    }
    try {      const names = await fetchNamesByAddress({        networkUrl: network.coreApiUrl,        address,      });      if (names?.length) {        setLocalNames(network.coreApiUrl, address, [names,]);      }      return names || [];    } catch (e) {      console.error(e);      return [];    }  }));

In order to reduce network traffic, Heystack also caches names in the browser's local storage.

A common design pattern in Stacks 2.0 apps is to check if a user has a registered BNS name (only 1 name can be tied to an account) and display that name in the app where appropriate. If the user doesn't own a BNS name, the wallet address is used as a stand in. Often, the wallet address is truncated to avoid displaying an overly long string.

The account name component in src/components/user-area.tsx demonstrates this design pattern:

...const AccountNameComponent = memo(() => {  const { user } = useUser();  const address = useCurrentMainnetAddress();  const names = useAccountNames(address);  const name = names?.[0];  return <Text mb="tight">{name || user?.username || truncateMiddle(address)}</Text>;});...

Development walkthrough video#

If you would like to learn more about the Heystack application and how it was developed, the following video presents specific implementation details.