Sign and Submit Transactions¶

Introduction¶

This guide covers the @parity/product-sdk-signer package, which gives your Product a typed, host-aware signing interface for deriving accounts and signing payloads (raw bytes or full transactions) from inside a Polkadot host container. The SDK exposes a single orchestrator, SignerManager, that wraps both the production host path (Polkadot Desktop) and a deterministic dev path behind the same Result-typed API.

Prerequisites¶

Before starting, ensure you have:

A Polkadot Product project running locally (see Set Up Your Project) with a TypeScript toolchain
Node.js 20 or later with ESM support (@parity/product-sdk-signer is ESM only)
Polkadot Desktop to run your Product inside a host container (see Install Desktop and Pair)

Note

To test signing without a host container, use manager.connect('dev'). This loads the standard Substrate dev accounts (Alice, Bob, and others) locally and does not require Polkadot Desktop. See Test Without a Host.

Code examples

The snippets in this guide are standalone; each one illustrates one concept and can be pasted into your Product independently. They are confirmed working with Polkadot Desktop and @parity/product-sdk v0.9.0.

Install the SDK¶

You have two installation options depending on your needs:

Umbrella package (recommended starting point): Install the full SDK in one command. Convenient when your Product uses several SDK features (signing, chain client, cloud storage, and more) and bundle size is not a concern.
```
npm install @parity/product-sdk
```
Individual package: Install only the signer. Keeps your bundle smaller and makes dependencies explicit; switch to this later as a bundle-size optimization.
```
npm install @parity/product-sdk-signer
```

All import paths shown in this guide work with both options.

How Product Accounts Work¶

Every product-scoped account is identified by a ProductAccountId tuple:

dotNsIdentifier: The dotNS identifier of the Product requesting the account, for example the .dot name your Product is loaded under.
derivationIndex: A non-negative integer chosen by the Product. Index 0 is the conventional default; higher indices give you additional sub-accounts within the same Product.

The same (dotNsIdentifier, derivationIndex) pair always yields the same public key, so your Product can reproduce the same address across sessions without persisting it.

Per-Product isolation is a privacy feature

app-a.dot and app-b.dot produce different addresses for the same user. This prevents passive on-chain correlation across Products. Sharing an account across Products requires explicit permission; it is never the default.

Set Up Signer Manager¶

Construct SignerManager once and hold it for the lifetime of your Product. Always set ss58Prefix and dappName explicitly. Use the onConnect callback to request any resources your Product needs immediately after connection; the callback fires exactly once per connect and re-fires automatically after any auto-reconnect.

import { SignerManager } from '@parity/product-sdk-signer';

const manager = new SignerManager({
  ss58Prefix: 0,
  dappName: 'my-product',
  onConnect: async (_account, { requestResourceAllocation, signal }) => {
    try {
      const outcomes = await requestResourceAllocation([
        { tag: 'BulletinAllowance', value: undefined },
      ]);
      if (signal.aborted) return;
      if (outcomes.some((outcome) => outcome !== 'Allocated')) {
        // Degrade gracefully: the capability is unavailable, not fatal.
      }
    } catch (cause) {
      // Typed host error; the connection itself is unaffected.
    }
  },
});

ss58Prefix: The SS58 address-format prefix for the target network. Use 0 for the Polkadot relay chain.
dappName: A human-readable name for your Product, shown in Desktop UI.
onConnect: Fires once per connection transition. Request the resources your Product needs here, before any signing call is made.
ctx.requestResourceAllocation: The one call in this package that throws instead of returning a Result, so wrap it in try/catch. Each outcome is 'Allocated', 'Rejected', or 'NotAvailable'; treat anything other than allocated as the capability being unavailable.
ctx.signal: Aborts if the user disconnects while the request is in flight. Check it before acting on the outcomes.

AutoSigning is not grantable yet

It is the resource most worth requesting and the one you cannot depend on: both the Android and iOS wallets return NotAvailable for it today. Keep per-transaction signing as the real path. See Allowances and Permissions.

Connect to the Host¶

Call connect() to establish a session with the host and discover available accounts. connect(), selectAccount(), getProductAccount(), and signRaw() all return a Result; always check .ok before accessing .value. (getSigner() returns a nullable directly, not a Result.)

Each step below is a self-contained function over the manager you built above, so you can paste them one at a time.

async function connectAndSelect() {
  const connectResult = await manager.connect();
  if (!connectResult.ok) {
    // HostUnavailableError when running outside Desktop
    console.error(connectResult.error.message);
    return null;
  }

  const accounts = connectResult.value;
  if (accounts.length === 0) {
    // Connected, but the host derived no accounts for this Product.
    return null;
  }

  // Auto-select the first account if none is already selected
  if (!manager.getState().selectedAccount) {
    const selectResult = manager.selectAccount(accounts[0].address);
    if (!selectResult.ok) {
      console.error(selectResult.error.message);
      return null;
    }
  }

  return manager.getState().selectedAccount;
}

A successful connect can still yield zero accounts

connect() resolves with ok([]) — not an error — when dappName is unset or the host rejects the derivation, typically because the .dot identifier is not registered for that user. Check the length before indexing, or accounts[0].address throws on a path the SDK treats as normal.

connect() defaults to the host provider. Outside a host container it returns HostUnavailableError; use connect('dev') for local testing instead. See Test Without a Host.

Get a Product Account¶

getProductAccount requests the product-scoped account for a given dotNsIdentifier from the host. This is a host-only API; it returns HostUnavailableError when the active provider is 'dev'.

async function loadProductAccount() {
  const accountResult = await manager.getProductAccount('my-product.dot', 0);
  if (!accountResult.ok) {
    console.error(accountResult.error.message);
    return null;
  }

  return accountResult.value; // SignerAccount
}

The returned SignerAccount exposes:

address: The SS58-encoded address for the current network.
publicKey: The raw 32-byte public key.
name: An optional display name, or null.

Sign Arbitrary Bytes¶

Use signRaw to sign an arbitrary byte payload with the currently selected account. This is useful for off-chain authentication, message proofs, and any use case that does not require a full transaction.

signRaw returns a Result<Uint8Array, SignerError>; it never throws. Always check .ok before accessing .value.

async function signMessage() {
  const account = await loadProductAccount();
  if (!account) return null;

  const selectResult = manager.selectAccount(account.address);
  if (!selectResult.ok) {
    console.error(selectResult.error.message);
    return null;
  }

  const payload = new TextEncoder().encode('hello polkadot');
  const result = await manager.signRaw(payload);

  if (!result.ok) {
    console.error(result.error.message);
    return null;
  }

  return result.value; // Uint8Array - the raw signature
}

Sign and Submit a Transaction¶

To sign a transaction, get a PolkadotSigner from SignerManager and pass it to the signAndSubmit method from polkadot-api (PAPI). The SDK handles routing the signing request to Desktop, which renders a signing modal and forwards to the Polkadot App.

@parity/product-sdk-signer provides only the signer interface; chain connectivity uses polkadot-api directly. Set up your PAPI client separately:

import { createClient } from 'polkadot-api';
import { getWsProvider } from 'polkadot-api/ws-provider/web';
import { dot } from '@polkadot-api/descriptors';

const client = createClient(getWsProvider('wss://rpc.polkadot.io'));
const api = client.getTypedApi(dot);

The dot descriptor is the typed API surface for the Polkadot relay chain. Run npx papi add dot in your project to pull or regenerate it.

async function transfer() {
  const recipient = 'INSERT_RECIPIENT_ADDRESS';

  const account = await loadProductAccount();
  if (!account) return null;

  const selectResult = manager.selectAccount(account.address);
  if (!selectResult.ok) return null;

  // getSigner() returns null if no account is selected
  const signer = manager.getSigner();
  if (!signer) return null;

  const tx = api.tx.Balances.transfer_keep_alive({
    dest: recipient,
    value: 1_000_000_000_000n,
  });

  return tx.signAndSubmit(signer);
}

Handle Signing Errors¶

Two outcomes are worth handling explicitly: the user rejects the request, or the signing session times out.

import {
  HostRejectedError,
  TimeoutError,
} from '@parity/product-sdk-signer';
import type { PolkadotSigner } from 'polkadot-api';

async function submitOrReport(
  tx: { signAndSubmit(signer: PolkadotSigner): Promise<unknown> },
  signer: PolkadotSigner,
) {
  try {
    return await tx.signAndSubmit(signer);
  } catch (error) {
    if (error instanceof HostRejectedError) {
      // The user dismissed the signing prompt on the Polkadot App
      return null;
    }
    if (error instanceof TimeoutError) {
      // The signing session expired before the user responded
      return null;
    }
    throw error;
  }
}

HostRejectedError: The user explicitly denied the request. Return the user to a stable state and let them retry.
TimeoutError: The signing session expired. Treat this the same as a rejection.

Design for async latency

Signing is asynchronous because the Polkadot App runs on a separate device. Show a non-blocking pending state rather than freezing the interface, and make sure your retry path is idempotent in case the user attempts the same action twice. There is no push notification when the phone is waiting, so a stalled-looking action is often an unanswered prompt.

Test Without a Host¶

During development, use connect('dev') to load the standard Substrate dev accounts (Alice, Bob, Charlie, Dave, Eve, and Ferdie) without needing Polkadot Desktop. The signing API is identical — only the provider changes.

async function devSignRaw() {
  const result = await manager.connect('dev');
  if (!result.ok) return null;

  const [alice] = result.value;
  if (!alice) return null;

  const selectResult = manager.selectAccount(alice.address);
  if (!selectResult.ok) return null;

  const signResult = await manager.signRaw(new TextEncoder().encode('test'));
  if (!signResult.ok) return null;

  return signResult.value; // Uint8Array - the raw signature
}

Four methods are host-only

getProductAccount, getProductAccountAlias, createRingVRFProof, and getUserId return HostUnavailableError when the active provider is 'dev'. getUserId is easy to miss: Identity recommends it for reading a personhood username as a display name, so a Product that does that renders fine in a Host and fails under the dev provider.

Limitations¶

The package is ESM only; your Product's build pipeline must support ESM imports.
SignerManager.destroy() is terminal. After calling it, all subsequent method calls return DestroyedError. Use disconnect() for a reversible reset.
Account persistence across page reloads requires the host to expose localStorage. Outside a host container, persistence silently no-ops.

Where to Go Next¶

Guide Store Data on Chain

Your Product can sign; next, use that signer to store content on the Bulletin Chain and fetch it from anywhere by CID.

Store Data on Chain
External PAPI Docs

Reference for the typed PAPI signer interface that @parity/product-sdk-signer exposes.

Visit Site
External Product SDK API Reference

The full product-sdk surface beyond this recipe: every package, class, and method.

Visit Site

Last update: September 2, 2026
| Created: June 16, 2026