b z I Flow Workshop Fast Track Your Onchain App I ETHGlobal Prague 2025

[Music] I think we can pretty much get started now. I hope you guys can hear me. So, um, hey everyone, I'm BC Devil at Flow Foundation. So, if you're hacking at Elobal, which obviously you are, and want something that's fast, easy, and powerful, you're in the right place. In this workshop, uh, we'll show you how to build a project on Flow from scratch, whether you're an experienced Solidity dev or new to web 3.

So, let's get started. Let's start with the obvious question. Why should you even care about Flow? There's so many changes today. Uh, and why does this one makes, you know, your time worth worth it?

So, let me show you. If we take a step back uh back in time and look look at the past, there were very few onchain apps in the market. But at one point, we actually see this massive spike. Can anyone get here guess what happened? Any guesses what caused the spice?

Yeah. No, no, but I I think I heard something some whispers. All right. So, what I heard was CryptoKitties, right? So, it was actually CryptoKitties.

It was the first rival blockchain game. It made people believe that there was a reason to build DAPs. It was so rival that it actually broke the Ethereum network. It literally shut the whole Ethereum network down. So the future of finance was suddenly like yeah not that scalable.

Uh our team is actually the ones who built cryptokitties. So we knew that something had to change. It didn't really make sense that users had to spend like five bucks on a kitty but the gas cost 50 bucks, right? from scaling and economic sense. It also doesn't make sense that the user had to know what a crypto wallet is.

Write down a seed phrase, going to an exchange, buying ETH, transferring ETH, so on, just like approving transactions, right? No one really wants to do that. Uh so we had like this use UX uh barrier as well. Another limitation is that for developers like you guys like most cases if you do anything new on solidity a smart contract you would have it audited. We paid thousands of dollars to two different auditors and they were still bucks in the code.

It's just very very difficult to actually write anything uh new uh in the solidity. So with major brands like NBA who wanted to work with the cryptokitty teams, we knew that we needed a network that could scale to the billions. So that's why Flow was built. It was built from scratch to fix all those problems with us UX and scale. Um it's built for real apps, real users.

Uh we like to say that Flow is made by developers for developers. We are consumer app developers. So we know all the pain points. We're not just pro protocol engineers. um ad flow you get native account abstraction and gasless UX.

What that means is that like just imagine users interacting with your app without even realizing it's on a blockchain. That's huge. They don't have to like like just when you use the internet you don't really need to know which protocol like SS SSL and uh TLS what that is. Uh in terms of soft finality it's super fast. We have less than 4 seconds in softity.

or block times are 800 milliseconds that this makes flow the fastest L1 EVM chain. So if you want something that's very high performance, you should build in a flow. If you're solidity dev, well flow EVM just works. We have full EVM equivalents. So you can just plug and play existing solidity code with a CK proofs like um you can also just use that the existing tool on EVM your favorite ones like mammask, remix, hard hat, foundry that all works on flow.

If you want advanced smart contract locker trick, you could also use cadence to just takes take it to the next uh level in security and also um have something like more resource oriented. We created a resource oriented programming language that was meant for digital assets such as NFTs and tokens. Um in terms not only that we have two environments we have both the cadence and EVM side which are totally composable so interoperable with each other. This is where it gets really interesting. So if you have existing solidity code, it can actually utilize some of the special powerful features from cadence uh and vice versa uh even in atomic like single atomic transaction.

So you get the best of both worlds and yeah uh we trusted by major brands NBA topsh shot NFL all day Mattel Disney even today we announced that Disney plus subscribers every month they receiving Disney NFTs all on flow most people don't know this but ticket master is the largest NFT collection in the world with 80 million NFTts all on flow this would have cost billions of dollars to do on Ethereum But on flow it costs pennies and we're also me resistant. So the question is how do we actually do all this? Well uh just to go a bit back actually can I do that? Yeah we basically looked at the problem uh if anyone is familiar with the blockchainma it basically just means that well in order to scale like um well usually you have to be like decentralized. you there you usually have to do some kind of trade-off for traditional blockchains like Bitcoin and Ethereum they chose decentralization and security but it just meant that they couldn't really scale for Salana well they had to be centralized in order to actually have a high TPS so we looked at this problem and thought how can we actually solve this and the way we found out was by logging a bunch of engineers in a room until they found out and what they found out was what if we just separated like the jobs of these like nodes.

So we created our own multi-road node architecture where we have data availability that's our access node sequences sequencing it's a collection nodes and consensus execution execution of course settlement verification nodes those things you already see on different blockchains where they specialize but we actually have specialized nodes that allow us to um basically create this like much more meresistant blockchain much more performant blockchain and we also have um the most gas efficient blockchain Deoid they created a report where they tested all the different blockchains how much energy consumption they actually do and FL came out to be the most energy efficient. It's cheaper like it's 12 times cheaper to mint an NFT on Flow than actually doing a Google search or Instagram post. It's that gas efficient. We have two tracks. One is the best killer app on flow and the second one is best crosschain defy on flow.

And we are giving out $10,000 in bounties. If you go to the first one, here's some inspiration. These apps that you see right here are killer apps. We had CryptoKitties. It's a ETH global hackathon project.

We had Uniswap. It's a E global hackathon project. They all started here just like you guys. And they didn't just win hackathons. They ended up becoming billiondollar protocols.

So what is a killer app? It's something that has the potential to basically onboard a million users or um create billion dollars of like TVL and like market cap. Um yeah and what like what your version looks like uh might look uh differently but the key here is just that these like um projects have invented a new primitive. Cryptokitties was the first ESC 721 uh standard. the NFT standard that is used today, widely used and we are actually the author of that.

Unis swap did the first automated market maker um and did a month of new smart contracts. Today we probably have like six to nine really really good smart contracts that's useful and we believe there'll be many many more but in order to do that you need a smart contract language that can actually provide you this because solidity is very very limited. Um, and yeah, actually a fun fact is also the OpenC first like first version is the fork of CryptoKitties marketplace. So, it all traces back to the cats. Uh, track number two is the best crosschain DeFi.

So, what does that actually mean? Well, now you already know that Flow is super performant is the fastest L1 EVM chain. Well, what can you do? Well, we supported by layer zero, relay, seller, hibernate, acceler. Uh, so we're very very liquid.

We have you have instant when you build on flow you have instance to global liquidity. Uh we also have like great like stable coin like farms where you can get like great APR. Um this then allows you to do different yield strategies right you can basically pull liquidity from anything. Anyone can buy whatever coin they want from other chains and actually pull it to flow. We have plenty of liquidity also with stables.

uh you can create 10x better uh user experiences on flow because on flow with cadence you get like features like um um what is it onchain randomness and also batch transactions. So batch transactions basically allow you to if anyone have tried to do yield farming before you have to do a bunch of steps a bunch of uh approvals and transactions in order just to do simple yield farming well you can do that in a single atomic transaction of flow uh and we also have reference locks I'll make sure to provide these slides in our flow page at e global so yeah let's uh try and do some demo let's show you how you can easily deploy on flow um just get started to it. Let's see if this works. So first you create your meta mask like this and then you have your metam mask right next step is that you want to fund it. So you just Google flow faucet token and then you do like the IQ test and now uh you go to developers.

flow.com using flow and add the flow EVM test net and then you can see your font funds. Then you go to remix IDE and from there you'll want to like yeah add your contract. Here we do onchain randomness. Uh so there's a simple randomness function there in this contract and we just deploy it by injecting the minus that we just created.

So now we have deployed it. It was like that easy. And that that's say it takes like less than five minutes. And now we can call a bunch of functions. So now we can call like we try and test it.

We can call our onchain random function. we give it like a um different kind of um range from 1 to 10. We test it. We see okay it didn't it ended up being seven. Uh so that's how you can pull it onchain randoms is very like like useful but I'll get to that later.

And then now you can set up your front end to actually interact with the contract we just deployed. You just uh here we do some vibe coding. You can open cursor. we show you. Okay, we drop and fl copy and paste the contract to them.

I just prompt it easily like okay I have this solidity contract deployed on flow EVM test net uh create um a front end for me that uses wag like a tool that I like to use um for EVM and then allow us to use the random function um and now we're just going to like let it think for a bit we'll also going to guide you more about it and there we see okay now we created a front end that took around like yeah five minutes and we now have to do a bit of debugging. We need to make sure that it actually works. So, we would usually check in order to debug, you would have to check, okay, does it use the right contract address? Uh, we'll try here. You see that I search for it just chain um and I end up finding it in this file.

See, there we go. It's around here. So, the contract address, we need to fish fetch that from where we just deployed it. And that's what I'm going to do in a bit. um right here.

You go to a scan, you look at the contract address, it's right here. So, I copy that and just replace it. Um then another thing that's very common when you use something like cursor for EVM is that you need the chain ID. So, here we see it's written wrong. The ID it says 9342.

We go to developers.flow.com flow.com once again go to EVM using EVM and then we just get the test net uh chain ID and just replace that and now our our front end basically works. So that's one example of how we can just survive code it uh and now we test it and we see hey it works uh we basically able to fetch onchain random numbers.

Why do you want things on chain? Well that's because then you don't suddenly need a third offchain third party provider. you can have something that just runs forever basically for free for you. Uh so flow is a very very powerful computer. Um we had a case where like another thing that's also pretty rare on flow is that you can have store all the onchain metad like you can store all the metadata on chain.

We had cases with NFT collections. If anyone knows clonex does anyone have anyone heard about it or one person clonex. It basically are NFT collection that got acquired by Nike and they closed down and all of a sudden the people who have spent hundreds of thousands of dollars on these NFTts suddenly lost the meta data. They couldn't see the images anymore because the server went down. On flow you can actually store that fully on chain and because we're the most gas efficient it makes the most sense to do it on flow.

So flow event there's the links here that I used developers offlow.com I'll make sure to add the resource of this this slide it should also be on our flow e global flow page there's the blog explorer on evm there's the test net foret that you'll be using if you have been through at our booth you'll know that you can scan a QR code and go to our telegram group there in our telegram group we have like a VIP developer support but not only that there's a Google form you can fill out and there will send you real mainet tokens because we'll just show you how easy it is to get to mainet. Uh because that's the big biggest thing about this the just to create a proof of concept right for you guys but you can launch it on mainet. All contracts also upgradeable so even if you have bugs you can get those fixed and when you are ready you can suddenly freeze the smart contract so people can trust that the code won't change. In terms of low cadence, if you're a beginner or just it actually doesn't matter if you're also experienced um you might want to try this uh resource oriented like language.

Um there I have built a project um myself. It took me like three days. It was like a decentralized 5G network called WLE. I used different like um um advanced flow features. Uh there I use magic link for custodial uh wallets.

We sponsor gas there. So people don't need to know the blockchain. They just sign in with the email and everything just runs easily. They can click on mint and no transaction popup comes up. Uh we use secure onchain randomness there.

Um again and crossvm metadata views because you can store the metadata on chain. So you can actually have it on EVM on OpenC where you don't need to set up your own server for it. We also use something called a hybrid custody account linking which allows you to create a parent wallet. Let's say you like let's say it was a media mask wallet or a flow wallet then it can actually link to your custodial wallet to make sure that these assets even if the my app shuts down they still you can still control the things that were in your like let's say water app or NBA topsh shot app or Disney pinnacle apps you will always own your NFTs no one can take it from you we have key um key rotation cycling so that basically allows you to scale uh like do a lot of transactions within just a single account. That's also really really rare.

Usually when you have accounts you would have to do one transa transaction wait for it to pass and then you can do another one. On flow you can actually have the same public key thousands of times millions of times and just run a million transactions at the same time from one account. Crosschain uh D5 resources we have them here. Uh again I'll share the uh links um on a page but uh we are fully supported by layer zero v layer which is also here. Um if you want to do cross bounties they do ck proofs they also support flow.

Yeah, and you know where to find us. There's the telegram group developer docs on flow um the test net foret if you want to do test net there's a booth uh and our e global page which should be a single source of truth. Oh sorry I think I still have some time. Um then for judging uh judging tips well I just want to be transparent. I know you guys, some of you are really here to win, right?

Uh I love that. I love competitiveness. So just to be transparent, these are our criterias. It's it might be a bit difficult to read from here, but I'll I'll basically explain them. We have six criterias.

We look at technology. So is it a clean implementation? Do you use advanced features on flow? Um the completion, uh is there a live demo that works or is it just like a broken link or video? Um protocol usage.

How much of flow do you use? like you use account linking or cadence or gasless UX. Gasless UX is pretty easy to do. Um the user experience is this like a smooth intuitive uh like front end that you have made. Um so of course it's nice if it's polished adoption.

How likely is it that real users would actually use this? That's also important. And then originality. The thing is um originality is like special like um you don't have to come up with the ideas yourself always like just imagine cryptokitties was inspired by Pokemon cards unis swap was actually inspired by noses uh which so they basically sort of forked the idea uh openc again it came from the cats uh their marketplace so you don't have to worry too much about it uh but this is to give you an idea of the criterias after this hackathon we still very much want to support you guys. Uh you'll be part if you submit at uh flow um your project then we'll basically uh onboard you to our grants programs.

We have a first round of grant now. We can even even help you this weekend if you're interested. The deadline is June 30 where we give out 50,000 flow per pool. Uh and yeah, this is a QR code for our telegram. I definitely recommend joining our telegram group.

There there'll be a form and there you can basically give us your mainet address so we can give you some tokens. Flow is powerful uh but simple enough to ship something amazing this weekend. Uh so if you got questions, we're here to help. Check the developer portal. Uh jump in e global uh discord for at the flow channel and ping us.

Uh and yeah, just go build something weird cool preferably on flow. And remember, CryptoKitty started as a simple hackathon project just like yours. Good luck, guys. Any uh questions? Yes.

They didn't support testing. Oh, sure. Yeah. So, that is true. Like the testing environment is still like a work in progress.

That's why like for if you're doing something crosschain defi that's why we actually recommend just doing it on mainet again flow has very very low gas. So basically when we send you air drop you some mainet tokens you have the full liquidity everything just works there. Um so that's basically how we can solve that for you. Any other questions? You can ask anything even like my favorite brand of ramen or Yeah.

Yes. Should I wondering if uh the NFT minting is um the same as any EBM chain like uh or you you maybe deploy the metadata on uh on the chain directly for you. So so NFT mending on EVM is exactly as NFT mending on EVM. So it's fully EVM equivalent. So you don't have to do any code changes.

The thing is with like onchain states like you can do things in solidity and store it on chain but we also have the cadence side where you can like store it there in cadence code is very normal that we just have all the meta data there but if you're used to just doing the things on like EVM just do that um all you need is the RPC endpoint which was shown in the workshop. Yeah. Yeah, it's I think it's for live stream for for clonics. You said that you could just deploy the images on chain. So how much data can you actually put on chain with reasonable gas cost?

Yeah. Uh well basically I feel like there's not really much of a limit. Uh again, flow flow storage uh if you want to store let's say 100 megabyte of data right on flow that would usually just require you to have like uh 40 cents to like store that data. So you can store as much data as you basically want. Storage is very very cheap.

Okay. Thanks. All right guys, thank you so much. Good luck. [Music]