--- title: "Build" description: "Build Polkadot Product capabilities with product-sdk packages for signing, on-chain reads, decentralized storage, off-chain pub/sub, and local persistence." categories: "Apps" url: "https://developers.polkadot.com/apps/build/" word_count: 1304 token_estimate: 2590 version_hash: "sha256:ef9e35e567d08c78ce921068d7c88836369e3675217f902b72750ac333ca65d6" last_updated: "2026-11-13T11:04:04+00:00" --- # Build The Build section is a cookbook of focused recipes, one per [`product-sdk`](/apps/product-sdk/) package; each recipe takes a single capability and walks you from an empty project to working Product code. They apply no matter how you started: a [Quick Start](/apps/quick-start/) deploy (RevX or CLI) or a project you [set up yourself](#set-up-your-project). Pick the capability your Product needs, in any order; the recipes are ordered by how little they ask of you, and the first one requires no account and no tokens. :::tip[Go deeper on any package] Each recipe walks one path through a package. For the concepts behind a package — what it is, when to use it, and its core types — see its overview in the [Product SDK](/apps/product-sdk/) section. For the complete surface (every class and method), see the [Product SDK API reference](https://paritytech.github.io/product-sdk/). ::: :::note[Products Devnet] Building on the PCF Products Devnet (`devnet` preset)? See [Use platform services from the SDK](/apps/build/platform-services-sdk/). ::: ## Set Up Your Project Every guide assumes a Product project running locally in [Polkadot Desktop](/apps/get-started/). The steps below apply no matter how you bootstrapped your Product: a [Quick Start](/apps/quick-start/) deploy (RevX or CLI) or a project created from scratch. 1. Scaffold a project. Any framework that serves on `localhost` works; this example uses Next.js: ```bash npx create-next-app@latest my-product cd my-product ``` 2. Install the [Product SDK](https://github.com/paritytech/product-sdk): ```bash npm install @parity/product-sdk ``` 3. Start the dev server: ```bash npm run dev ``` 4. Open Polkadot Desktop and click **Skip (Dev only)**. ![Polkadot Desktop showing the "Skip (Dev only)" button](/images/apps/build/start-a-local-dev-loop/start-a-local-dev-loop-01.webp) 5. Type `localhost:3000` (or your dev server's port) in the address bar and press **Enter**. Desktop recognizes `localhost` as a whitelisted origin, skips `.dot` resolution, and loads your Product directly from the local server. ![Polkadot Desktop showing a local Product loaded from localhost:3000](/images/apps/build/start-a-local-dev-loop/start-a-local-dev-loop-02.webp) Your Product is now running inside the Polkadot Desktop sandbox, served from your local machine. Live reload works through your dev server's hot module replacement: edit, save, and watch the change appear in Desktop. The sandbox and permission prompts apply exactly as they would for a published `.dot` Product, and no Proof of Personhood or funds are needed to load from `localhost`. ## Capabilities
- **Read On-Chain Data** --- Your Product needs to show live balances, storage, and chain state. Reads are unsigned: no account, no tokens, no infrastructure to run. [→ Read On-Chain Data](/apps/build/read-chain-state/) - **Sign and Submit Transactions** --- Your Product needs to act on chain on the user's behalf. Derive a per-user account and request signatures; every approval happens on the user's phone. [→ Sign and Submit Transactions](/apps/build/sign-and-submit/) - **Store Data on Chain** --- Your Product needs content that outlives a session: profile photos, published posts, file uploads. Write to the [Bulletin Chain](/reference/apps/infrastructure/bulletin-chain/) and fetch from anywhere by CID. [→ Store Data on Chain](/apps/build/store-data-on-chain/) - **Publish and Subscribe to Off-Chain Data** --- Your Product needs real-time state between users: presence, typing indicators, multiplayer cursors. Signed pub/sub via the [Statement Store](/reference/apps/infrastructure/statement-store/), no fees per message. [→ Publish and Subscribe to Off-Chain Data](/apps/build/pub-sub-off-chain-data/) - **Persist Data Locally** --- Your Product needs to remember things on this device: preferences, drafts, cached values. Per-Product key-value storage backed by the Host, with no browser `localStorage` fallback. [→ Persist Data Locally](/apps/build/persist-data-locally/) - **Add a Smart Contract to Your Product** --- Your Product needs enforced, shared on-chain logic: a leaderboard, a registry, an escrow. Deploy a PolkaVM contract to Asset Hub and call it by name from your frontend. [→ Add a Smart Contract to Your Product](/apps/build/deploy-a-smart-contract/)
## The `product-sdk` Packages Each guide is built around one _primary_ package and weaves in _utility_ packages where they are needed. The full source is at [`paritytech/product-sdk`](https://github.com/paritytech/product-sdk). Here is what each package is for: | Package | What it does | Guide | |:-----------------:|:---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------:|:------------------------------------------------------------------------------:| | [`chain-client`](/apps/product-sdk/chain-client/) | A typed, host-routed client for reading on-chain storage, constants, and account state across one or more chains, with no RPC infrastructure to run. | [Read On-Chain Data](/apps/build/read-chain-state/) | | [`signer`](/apps/product-sdk/signer/) | Derives product-scoped accounts and requests signatures, routing every approval to the user's [Polkadot App](/reference/apps/hosts/polkadot-app/). Your Product signs without ever handling keys. | [Sign and Submit Transactions](/apps/build/sign-and-submit/) | | [`cloud-storage`](/apps/product-sdk/cloud-storage/) | A high-level client for the [Bulletin Chain](/reference/apps/infrastructure/bulletin-chain/), Polkadot's content-addressed storage. Uploads and retrieves data by CID, with chunking, manifests, and authorization handled for you. | [Store Data on Chain](/apps/build/store-data-on-chain/) | | [`statement-store`](/apps/product-sdk/statement-store/) | A pub/sub client for the [Statement Store](/reference/apps/infrastructure/statement-store/): publish and subscribe to signed, short-lived statements gossiped peer-to-peer off-chain. Ideal for real-time signaling between users. | [Publish and Subscribe to Off-Chain Data](/apps/build/pub-sub-off-chain-data/) | | [`local-storage`](/apps/product-sdk/local-storage/) | A per-Product, per-device key-value store backed by the Host, for preferences, drafts, and cached values that persist across sessions. | [Persist Data Locally](/apps/build/persist-data-locally/) | | [`contracts`](/apps/product-sdk/contracts/) | Typed calls to `pallet-revive` (PolkaVM) smart contracts on Asset Hub, resolved by name from a `cdm.json` manifest, for enforced shared on-chain logic and state. | [Add a Smart Contract to Your Product](/apps/build/deploy-a-smart-contract/) | These packages anchor the current recipes because their surfaces are stable. Other packages in the SDK ([`keys`](/apps/product-sdk/keys/), `crypto`, [`host`](/apps/product-sdk/host/)) will get recipes of their own as their surfaces stabilize. The guides also use these utility packages where relevant: - **[`tx`](/apps/product-sdk/tx/)**: Builds, signs, and tracks the lifecycle of transactions (used alongside [`signer`](/apps/product-sdk/signer/)). - **`address`**: Encodes, decodes, and validates SS58 addresses. - **`descriptors`**: Provides typed chain metadata for the [`chain-client`](/apps/product-sdk/chain-client/) Bring Your Own Descriptors path. - **`host`**: Provides low-level access to the Host API surfaces the higher-level packages build on. ## Umbrella or Individual Packages Most guides work with either install style. Guides built on `createApp`, such as [Store Data on Chain](/apps/build/store-data-on-chain/) and [Publish and Subscribe to Off-Chain Data](/apps/build/pub-sub-off-chain-data/), need the umbrella package, because `createApp` has no standalone package. Choose based on your needs: - **Umbrella package**: `npm install @parity/product-sdk`. One dependency that re-exports everything. Convenient when your Product uses several capabilities and bundle size is not a concern. - **Individual packages**: `npm install @parity/product-sdk-cloud-storage` (and so on). Install only what you use to keep your bundle smaller and your dependencies explicit. The import specifiers differ between the two — the umbrella exposes subpaths like `@parity/product-sdk/cloud-storage`, while the standalone package is `@parity/product-sdk-cloud-storage` — so switching styles means updating your imports. Start with the umbrella and switch to individual packages later as a bundle-size optimization. For the full tour of the SDK — `createApp`, the package family, React bindings, and testing without a Host — see the [Product SDK overview](/apps/product-sdk/).