So what’s the Cardstack Product?

Introducing the Card SDK, the CARD Protocol, and the Cardstack Hub

Chris Tse
Published in
16 min readAug 20, 2019


Chris Tse, Founding Director of the Cardstack Project, explains the strategy, the main components, and the economics of the Cardstack product — to create a thriving, sustainable marketplace for all ecosystem participants.

“I like Cardstack. I like the idea. But how can I use it? What is the product? What is the thing I can get my hands on? How can I experience Cardstack?”

Let’s start with this question: Who is in the ecosystem — who participates in the “Cardstack” way of doing things?

End users

They choose Cardstack because the user-friendly open-source software is cheaper and better than what they know today. They see this as a way to find the tools they need. What they are looking for is the best selection, the best price, and the best service. That is why we create a Card Catalog, to which open-source contributors can add all kinds of cards, from which end users can choose. This pool of software code provides a great selection of cards to use for payment, content, messaging, and much more. Instead of asking users to download 15 different apps and keep track of 40 different subscriptions, all of which (including individual features) they have to pay for separately, we offer them everything they need in one catalog — one that contains all cards and features for one flat rate, which makes this approach much better priced than the alternatives. The monthly subscription fee paid by the end user simply covers the rewards for the developers, who create the code, and the providers, who support the network by offering their services to the end users. Yet, while the catalog is well priced for each individual user, these subscriptions essentially fund the ecosystem, by rewarding everybody who contributes.


They want something that helps them to make money, but that is also easy to build. Currently, when developers try to build and sell an application, they have to pay for a server themselves, hoping that users will eventually subscribe and cover the cost. In the Cardstack Ecosystem, there will be low or no operating costs, as we shift the cost to the users. And the developer won’t have to worry about hosting either, which is provided by hosting service providers. More importantly, we offer developers a unified SDK, consisting of both the front-end and the back-end, allowing them to create, deploy, and sell their cards — their mini-applications — all within one system. There’s only one set of software, one Cardstack SDK in JavaScript to learn to use.


They help users host the software that is built by developers, similarly to hosting WordPress for a user. And that’s a sticky arrangement. Once you’re running your website or application with a certain provider, you’re likely to stick with that provider over time. The recurring revenue coming in through the users will create incentives for service providers who know how to operate in the cloud, including sustainable margins. Service providers want to know that it’s not a race to the bottom, so they will be able to run a successful business. On the other hand, users always have the choice to switch providers, if they are not content with the service provider hosting their blog, for instance — this is possible due to our open-source approach and the fact that our data is portable. So, we build one stack to manage and deploy on any containerized cloud. We use Docker, Kubernetes, and other cloud deployment software technologies, to ensure that anyone can operate a Cardstack-based service. People can take that open-source code (not only the framework, but also the UI code) for the features of the card and deploy it in any type of commodity cloud service. Yet, the cloud provider does not get the margins. The people who build on top of a cloud provider and offer support to the users — the Cardstack service providers — receive the margins. Eventually, this turns into a competitive market.


Businesses are groups of users who want dependability. They want the software they work with to be properly maintained. People in the open-source community are willing to pay more for an additional level of dependency, in case something goes wrong with a plugin or a certain database driver needs to be updated. They will pay for the support provided by developers and service providers who know what it means to build on Cardstack. Furthermore, our open-source technologies allow the stack Cardstack depends on — our database, our servers, or even the blockchain software — to be cost-effective. There is no license fee underneath, no cost going beyond the package value that we can provide to the end user. Businesses essentially want white-label software with open-source code as a core, and that is what we offer them.

How are the ecosystem participants connected?

Cardstack sits in the middle of this four-sided market between users, providers, developers, and businesses, offering each of them their respective set of experiences, while the token mechanism allows them to participate in the economic value of this network.

Developers provide users with a catalog of software code that takes the form of cards. It’s like an app store, where developers publish their apps, which users then download and use.

Developers and providers have an economic relationship. The developers build software, which is then hosted by service providers, who get paid for their services by the subscribed users who end up using the software. The subscription revenue, which the providers receive from the users, is collected in a reward pool — part of which is then distributed to the developers. After all, the developers are the ones who build the software the users are using in the first place, plus the ones who maintain and improve that software continuously. They are the ones whose code makes the users willing to pay. Thus, they earn a fair share of the reward, which is calculated based on actual usage analysis. This means: The reward goes from the user through the provider to the developer, so that both the provider and the developer get compensated fairly for their contribution to the network.

Businesses and providers are connected through the Tally Protocol, which calculates how much of the revenue each of them should get, based on actual usage data. How many gigabytes of storage, how many thousands of API calls — that’s all information that exists on-chain, off-chain, or in the cloud. Tally looks at the shared accounting between the businesses and the providers and determines how the network should distribute the money.

Businesses and users collaborate using Card Flow. Cards are objects that encapsulate data and functionality, but when they move between organizations — like an invoice moving in, a payment going out — that’s where business gets done. Between businesses and users, it’s all about the exchange of cards. This workflow system is the basic aspect of their relationship, combining a conversational UI with logistics and action-chaining.

The Card SDK

The Card SDK (software development kit) is a composable UI system, allowing developers to easily build card templates, which end users then use to make their own cards. The Card SDK is deployed to the Cardstack Hub, which is the server. But that server is unique: In most systems, the developers run the server, so the users’ files are stored in the developer’s data center, being controlled by the developer. In our situation, developers deploy their cards to the hub, which is run by service providers of their choice. This way, all users have their own hub, their own server, their own little personal cloud, where they have all their code — whether it’s for note-taking or music-making or image-editing. It is run by a service provider, but it belongs to them.

The Card Catalog

Using the Card SDK, developers create cards that they add to the Card Catalog. There are different types of cards:

A Content Card could be a blog post or an image you can edit. A Data Card could be a form to do a survey. An Asset Card is similar to a Data Card, but may track conversion rates through an external database, providing the information you need for your cryptocurrency exchange. For instance, an Asset Card tells you the USD value for a certain Bitcoin or Ethereum transaction. But content, data, and assets are much more than just screenshots — they are actually live and real apps.

An Action Card is more like a strategy. To name a few examples of what Action Cards can do: They allow users to send data, extract funds, convert their assets into other assets via decentralized exchanges, put their data into CRM (customer relationship management) software, publish content to the Web, get it distributed all around the world, and much more.

The user experience

Content, data, asset, action — all these cards go into the Card Catalog. Once they are in the catalog, they can be experienced by users in different ways.

A developer who believes in the Card UI and wants to build an entire stand-alone website, which is indistinguishable from what you see today, can compose the cards into an experience that takes up the full screen. Other developers may prefer to embed the card within their websites or workflows, just like a YouTube video. Alternatively, they could say, “I have enough capability within this website. I want to show a list of cards to pick, or a list of addresses to choose from when sending cryptocurrency!” An overlay allows the user to pick and choose between several cards. So, whether it’s standalone or embedded or in an overlay, they’re all just different ways of packaging these cards in the Catalog for the user to see.

Identity representation

Card-based identity representations make users’ lives easier, allowing them to say, “You know who I am.” Cards can represent a credential, a login, a username and password. In that sense, they are almost like ID cards, which users can use to bypass signups. Once they have a Credential Card from one site, they can go to another website or card-based experience without having to log in again.

A Subscription Card works similarly. If you subscribe to a hosting service, you can create content without worrying about limits of the free version. Plus, we offer cross-honoring, where the subscription is honored on various websites; as long as they all accept Cardstack’s subscription, the subscribed users get a pass through all of them. It’s almost like a class pass, where you can take yoga classes from anywhere in your town once you buy a subscription.

We cross-honor this subscription because it’s essentially a membership. It’s deeper than a payment. You’re joining a community. This could be a corporate membership, which allows you to access certain features that your company has paid for — with your Membership Card. It could also be a personal membership, offering you a nice little pool of new features if you go to the platinum tier.

It could also be a simple Contact Card containing personal information, which users can create and reuse for all kinds of different purposes and workflows.

Payment methods

People like Amazon because they have their credit card stored there; they like Starbucks because they can reload their balance whenever they need it. The Cardstack experience will offer these various payment methods too, so that users can choose how to pay. They can ask service providers to deduct against their balance, using a Reward Card, a Prepaid Card, or a Credit Card.

A major part of the CARD Protocol — the economic model that makes this ecosystem sustainable — is about using these identity and payment cards as the basic connection between different instances or service providers, allowing them to share and bill mutual customers. This is all part of the front-end, the Card UI, which contains templates, schema definitions, and data source mapping. But the idea is that all these cards, these mini-apps, get aggregated into a kind of super app — whether it’s stand-alone, embedded, or overlay.

The Cardstack Hub

The Cardstack Hub is a decentralized application server that powers the entire system, sitting between the cards and the rest of the world. The data sources it connects to could be devices, clouds, or blockchains (because the hub has plugins for Ethereum and supports integration with different smart contracts, it can treat the blockchain as if it were just another data source).

The cards that are built using the Card SDK can talk to any hub, enabling the hub to get the data it needs, to query, or to transfer content easily. If you want to send a card to another person, the inbox of that person is just another space or queue within that person’s hub. Our focus is to make the experience simple for the end user.

The Cardstack Hub is quite mature. It has been running on multiple apps and is running continuously in the cloud. This ensures that, if you make a transaction on the blockchain, it is automatically reflected in all cards that use the hub as a data source.

The CARD Protocol

To bring the Card SDK and the Cardstack Hub together in a decentralized way, we need the CARD Protocol.

If you only have one service and one SDK (for example, Instagram with an Instagram SDK), developers can only deploy their software to one company. But in our open-network approach, inspired by blockchain and implemented using open-source technology, we can essentially build a multi-currency payment and billing network.

The CARD Protocol allows a user to choose any service provider who runs a hub and say, “I pick you to help me store my image files, or manage my wallet, or count my sales, or process my credit card payments or cryptocurrency transactions.” Users are not limited to one provider or one hub. They can have different hubs and different service providers serving different cards, because one provider may be good at dealing with data, while another one may be better at dealing with a content management system. But it’s all built using the same Card SDK, thus offers one cohesive experience. And the Cardstack Hub is the server where it all comes together.

Users are customers who deposit money to pay the service providers. Their funds get accumulated in a reward pool. Based on the rendered service and billable usage, the service providers receive a portion of that reward pool, which they can withdraw. The hub reports the relevant data to the protocol.

A multi-currency payment network requires a few more aspects, as we want to shift the risk between the buyer and the seller; it should be as if they were exchanging money at the time the service was performed. Therefore, the market rates factor into the value of the currency the users choose as payment. The protocol has to figure out how much the user’s token or USD was worth at particular times. This is done through a market rate oracle — a service that keeps track of spending, due dates, currencies, exchange rates, etc. That information is captured at the time of purchase. If you pay in USD, the oracle determines how much USD was worth at that moment. And based on how much is left in this particular pool, you get the spendable balance. Let’s say you put in a British Pound; suddenly, Brexit happens and the British Pound loses half its value. In that case, your spendable balance would be halved as well. This means: As long as a user hasn’t paid for a rendered service, the user (not the service provider) will take the risk of the currency exchange. However, if the user has already paid for the service (before the value of the currency was cut in half), then the service provider would be the one taking the risk.

The CARD Protocol coordinates between these six aspects — deposits, market rates, billable usage, withdrawals, purchases, and spendable balance — to ensure that this is a fair network. When it comes to payments, you get what your underlying asset is worth; so customers can be billed in a fair and accurate way.

Tally keeps track of the market rates and determines the reward, which is an on-chain smart contract that locks the tokens and the equivalent tokens (if you pay in USD, we lock an equivalent amount of the stablecoin pegged to USD, so we can actually measure on-chain, with some off-chain conversion data, exactly what it’s worth).

To bill a user, we need to know how much of the offered service the user has actually used. Being deployed to a cloud, the hub reports this usage data. If there is a monthly subscription, it’s easy; you can just bill the users monthly, as long as they don’t cancel the subscription. But first, there needs to be some money that has been deposited; and that’s where the cryptocurrency wallet comes in. This wallet can come from the end user or from a service provider who manages the wallet for the user, depositing the user’s money into the stake pool on his behalf. This stake backs the value of the billing entry. If there are USD 100,000 worth of stake in this smart contract, you can feel confident that, if you bill the user up to USD 100,000, there’s enough money there you can withdraw. Though the billing will most likely happen on a side chain, it is always redeemable on-chain.

That billing ultimately funds the rewards for the service providers and the developers (which is calculated by Tally, running on the Cardstack Hub). It also concerns the service providers and businesses who want to have a say in how this network operates. For instance, this could be about the rate that open-source developers get for their work. If the portion of the developer’s revenue is too high, the service providers will not be interested in providing services, because they’re not making sustainable margins; but if it’s too low, the developers will not be interested in building the tools. The mechanism of the stake pool thus governs the network, to determine the values of these important percentages, so as to balance the interests of all four parties.

This is an overview of the tools we offer to ecosystem participants. Users can use Card Space to organize cards; they can use Card Flow to communicate and join networks. Businesses can provide their own price lists and use the Tally mechanism to bill for their services. These don’t have to be low-level services like the ones that providers bill for, but could be validation services, underwriting services, or quality assurance services.

This is the basic ecosystem that not only connects wallets, clouds, and chains, but also makes sure that this is part of the Web — that you can go to a domain and different card spaces, which are websites on Web 3.0. Once you join such a website, that on-ramp is part of the greater network.

To sum up: Cardstack is at the core of this four-sided market between users, developers, providers, and businesses. We want to provide everything the users need at a good price, with good services, and a good selection. We want our network to give developers the opportunity to reach the largest audience on the Web. We want to enable providers to compete on price, services, and geography. We want to allow businesses to white-label our software, to build blockchain-based or cloud-based networks that are collaborative, using Cardstack as the basic runtime to form relationships and reach users in new ways. Finally, the intersections between the users, the developers, the providers, and the businesses are important pieces as we create this full ecosystem, where all the participants and the value network are connected in a seamless way.

What’s next?

1. We are preparing for the beta launch of Card Folio, the alpha-version of which we open-sourced in January. It runs on the Cardstack Hub as the back-end. We have improved our integration with the Ethereum network, so you will be able to plug in your MetaMask and use Card Folio’s query engine. Once we have plugins to support other types of protocol, we will be able to make that your asset orientation — your wallet, your portfolio. That is a very important aspect of introducing people to not only blockchain, but also decentralized finance. This is going to be our first consumer-facing product.

2. Tally and the CARD Protocol are under active development, with Tally currently running on Rinkeby testnet. The CARD Token is the native token, to be used to redeem services. But we will also support other currencies; you can stake other tokens, like DAI or ETH, as a deposit to use Cardstack services, and the conversion will be done inside the smart contract.

3. Jen Weber, our developer who focuses on the Cardstack Framework, provides ongoing updates on the developer experience of the Card SDK. We are in the process of compiling comprehensive documentation, which will explain how developers can build cards using our SDK. Of course, it’s easy to build a powerful framework that is hard to use. The real magic is building a powerful framework that brings back-end and front-end concepts and packages together, but is so easy to use that, once you define a schema and some templates, suddenly you have a card that can get automatically deployed. Developers want to be successful immediately. That’s why we want to enable them to push their code into the catalog with just one command line. Our framework does all the hard work, so they can focus on the features of their cards.

At Cardstack, we believe that the Web can become a real software ecosystem — not just a ton of individual websites fighting for ad dollars or competing for pop-ups. There is an opportunity for us to reboot the Web, using cryptocurrency and blockchain as a way to make it a more decentralized network. It’s about digging deep and understanding what kind of open-source software that was developed in the last generation we can bundle together, to provide an experience that is as attractive as an Android or iOS ecosystem. With the right abstraction, the right bundle, the right tools, and the right ecosystem participants — acting in both their self-interest and the interest of the network — we’re going to get there, with Cardstack being a catalyst for the movement of Web 3.0!

Learn More

Star Cardstack on GitHub and join our Discord channel or our Telegram group and announcement channel to get all our latest updates.



Chris Tse

Technologist, designer, and founding director of the open-source @Cardstack Project. Building the experience layer of Web 3.0.