Ever thought making a blockchain-based ToDo app was a bit weird? Yeah, me too—but what if privacy is baked in from the start? 😎 Nobody needs the world to see your grocery list (or your top-secret chores). Midnight gets this; it even says “Not everything should be visible on a blockchain”midnight.network. So today I’m showing you how to build a privacy-first to-do list dApp on Midnight, step by step, with code examples and a sprinkle of humor. It’s gonna feel like the blockchain equivalent of wearing a spy disguise. By the end, you’ll be adding tasks with your secrets securely hidden.

I remember my first blockchain dApp: a simple task tracker on Ethereum. It was cool, but wow—the entire chain could see every task I added. That freaked me out more than a random bug in my code! With Midnight, we can do better. It’s designed so privacy is not just a feature, but foundationalmidnight.network. You basically get to decide which data is public and which stays hidden using zero-knowledge proofs (ZKPs)midnight.networkmidnight.network. In other words, your to-do items and user info can quietly stay under wraps while still being verifiable on-chain.

Why Midnight for your ToDo dApp?

Midnight is all about giving devs privacy-first powers. Here’s why it fits our to-do list use case:

• Selective Privacy & ZKPs: Midnight blends public verifiability with confidential data handlingmidnight.network. You can literally shield parts of your data (like which wallet created a task) so only authorized folks see itmidnight.network. Thanks to zero-knowledge proofs, you can still prove something happened on-chain without revealing the detailsmidnight.networkmidnight.network. For example, Midnight’s bulletin-board tutorial uses a ZKP so only the original poster can delete a messagemidnight.network – kind of what we’d want if each to-do were tied to its creator.
• Compact – TypeScript-ish contracts: Midnight’s smart contract language is called Compact, and it’s basically TypeScript for blockchainsmidnight.networkmidnight.network. If you know JS/TS, you’re in good shape; you won’t feel like you’re learning ancient hieroglyphics. Compact is statically typed, too (catching errors early)midnight.networkhackmd.io, and supports neat functional patterns. I love this because I can write code that looks familiar: for example, ledger defines the on-chain data structure and export circuit defines the functions.
• Developer-friendly tools: Midnight makes onboarding painless. There’s a Developer Hub, docs, and even a VSCode extension for Compact contractshackmd.iomidnight.network. They even have a test token faucet so you can get free testnet tokens (NIGHT/DUST) to play with your dAppmidnight.network. Seriously, jumping into Midnight feels smoother than wrangling a new blockchain toolkit.
• Compliance & Enterprise Focus: For the enterprise-minded, Midnight helps with designing apps that handle sensitive data by design. That means easier compliance if you ever deal with privacy regulations. IMO, having privacy built-in is just smart engineering.

So in a nutshell: Midnight lets you build that to-do list without shouting your secrets from the blockchain rooftops. 🙂

Setting Up Your Environment

Before we code our to-do contract, let’s get our dev environment ready. It’s mostly straightforward if you follow the steps:

1. Download the Compact compiler: Go to the Midnight GitHub devnet releases and grab the compactc compiler for your OShackmd.io. Unzip it into a folder (like ~/midnight-tools/compactc).
2. Verify installation: Open a terminal in that folder and run ./compactc --versionhackmd.io. If it prints a version, you’re golden. (If you hit an error about glibc, make sure your system has a recent GNU C Library as notedhackmd.io.)
3. Set COMPACT_HOME: Export an environment variable so the system knows where compactc lives. For example: export COMPACT_HOME="/absolute/path/to/compactc" export PATH="$COMPACT_HOME:$PATH"

hackmd.io. This lets you run compactc from anywhere.
4. (Optional) VSCode extension: If you use VSCode, install Midnight’s Compact extensionhackmd.io. It adds syntax highlighting, code completion, and templates for Compact contracts, making life easier.
5. Create your project folder: In your terminal, do something like mkdir my-todo-dapp && cd my-todo-dapp. You’ll keep your contract files and any front-end code here.

At this point, you have the tools. If you want to go further, you can npm init a JS project and later install @midnight-ntwrk/midnight-js-contracts to talk to your contract from a front end. But for now, we’re set to write the contract code itself.

Writing the Smart Contract

Alright, now the fun part – writing the contract. In Midnight (Compact), a contract has a ledger (its on-chain state) and circuits (functions that modify state). Let’s sketch a simple version of our ToDo logic:

include "std";
ledger {
  tasks: [String];         // an on-chain list of tasks
}
export circuit addTask(newTask: String): Void {
  ledger.tasks.push(newTask);
}
export circuit completeTask(index: U64): Void {
  ledger.tasks.remove(index);
}

(This is a hypothetical snippet in Compact syntax.) Here, ledger.tasks is an array of to-do items on-chain. Anyone with access could add or remove tasks by calling these circuits. In a privacy-first scenario, though, you’d likely restrict who can call which circuit. For example, we’d want only the task creator to be able to mark it complete. That’s where Midnight’s ZK and witness features shine. For instance, the official bulletin-board example makes sure only the message poster (verified by a proof) can delete itmidnight.network – the same idea we’d apply to our tasks.

Compact also lets you use witness functions – pieces of JavaScript code that handle private data off-chainmidnight.network. You might use a witness to check a secret key or signature before modifying the tasks, so the chain never actually sees your secret. (Cool stuff, right?)

Don’t forget: test and verify your contract before deployingmidnight.network. Write some tests or just simulate calls locally. In our simple example, you’d compile with compactc and then call addTask/completeTask to make sure tasks updates correctly. If something’s broken, fix it now – debugging on-chain is no fun. 😉

Once everything compiles and runs locally, compactc will generate TypeScript API definitions for you. This means your front end can import the contract and treat it like a normal TS library. But fundamentally, the contract code above shows the gist: using an intuitive TS-like language to define on-chain data and actions, all with privacy smarts under the hood.

Building the Frontend

Now that our contract is written and compiled, let’s hook it up to a user interface. This could be a simple Node script, a React app, or even a command-line tool. The key is: Midnight makes this part smooth with TypeScript integration. When you compile your contract, Midnight outputs TS classes for each circuit, ledger state, and any witnesseshackmd.io. That means your contract looks like a regular TS/JS module!

For example, after compiling, you might import your contract API and do something like:

const api = await Midnight.loadContract("TodoContract", /* keys */);
await api.addTask("Buy milk");         // call our addTask circuit
const tasks = await api.ledger.tasks(); // fetch the updated tasks list
console.log(tasks);

(This is pseudocode to illustrate the idea.) You’d use Midnight’s JS/TS libraries (for instance @midnight-ntwrk/midnight-js-contracts) to send transactions. The great part is, from your perspective it feels like calling functions on a local objecthackmd.io.

If you’re using React or another framework, you might wire up an interface that calls these functions. The experience feels much more like normal web development – except with built-in privacy. As one Midnight developer notes, you get “a seamless development experience using familiar tools”hackmd.io. Kinda neat, right? 🙂

Testing & Deploying

Alright, we have code and (maybe) a UI. Time to test on a network! Midnight has a Testnet that mirrors the real chain. You’ll need some test tokens (called DUST or NIGHT) to pay fees. Luckily, there’s a Testnet faucet where you can grab some free tokensmidnight.network. Go ahead and claim some to fund your account.

Next, deploy your contract. Midnight’s CLI or SDK will handle this (think of it like using Truffle or Hardhat). Once deployed, try adding and completing tasks on the testnet. Check that your privacy rules work: if you set it up so only the creator can complete a task, make sure that holds in practice.

This is a sandbox, so don’t be afraid to mess around. Midnight’s Testnet is meant for exactly this: “a reliable environment that simulates the conditions of a live mainnet”midnight.network. Once everything looks good, you could even deploy to the live chain. But even as a test exercise, you’ll have built a full dApp!

Conclusion

Phew, we did it! 🎉 You’ve seen how to build a privacy-first to-do dApp on Midnight from scratch: why Midnight’s approach rocks, how to set up your tools, how to write a Compact contract with ledger and circuits, and how to hook it up to a front-end.

The key takeaway: Midnight blends the ease of TypeScript development with powerful zero-knowledge privacyhackmd.iomidnight.network. We treated our tasks like any app data, but we didn’t sacrifice confidentiality. Think about it: a to-do list where only you (or your approved audience) see the tasks – that’s kind of a game-changer. IMO, once you try it, you’ll wonder how we ever lived with totally public blockchains.

Ready to take this further? Maybe add user authentication, encrypted task details, or integrate a real crypto wallet. Midnight’s docs and the developer community have tons of resources. But hey, even our simple todo is now proudly privacy-first, and you built it yourself – nice job! 🙂

If you have questions or ideas, dive into Midnight’s docs or Discord. Who knows, your next dApp might be the hit that finally makes fully private blockchains mainstream. Good luck, and happy coding! 🚀

Sources: Midnight documentation and tutorials midnight.networkhackmd.iomidnight.networkmidnight.network.