Build a web app

Ship Senddy in a browser app with social login, session tokens and gasless deposits. The production checklist.

This is the shape of a production integration, taken from apps running on Senddy today, including HOODS on Robinhood Chain. Read it once before you build, and again before you launch.

The shape#

Embedded wallet ──signs──▶ private keys (derived on the device, never sent anywhere)
        │
        ├──signs──▶ deposit authorization ──▶ Senddy relay ──▶ pool
        │
        └──user's login token──▶ your /api/session-token ──▶ Senddy /session ──▶ sst_ token
                                                                     │
                              @senddy/client ◀───────────────────────┘

Three facts shape everything else:

1. Users never need gas. Deposits are a signature that Senddy relays. Sends and swaps are proofs that Senddy relays.
2. The browser holds no API key. It holds a short-lived session token your server mints per user.
3. Private keys come from a wallet signature and the pool address. They're derived on the device and never leave it.

1. Packages#

npm install @senddy/client @senddy/core viem

Plus your login provider. Embedded-wallet providers such as Privy work well, because every user gets a wallet without a browser extension.

2. Login and wallet#

Any provider that gives you a viem WalletClient for the user works. Two settings matter:

• Prefer embedded wallets. Key derivation signs typed data at the start of each session. With an external wallet that's a popup every login.
• Allow your chain. Robinhood Chain (4663) must be enabled in your provider's dashboard.

3. Session tokens#

Add one server route that verifies the user's login and mints a Senddy session token. Authentication has the code. Pass the provider to the client as sessionToken.

4. The client#

const senddy = createSenddyClient({
  publicClient,
  walletClient,          // the user's embedded wallet
  chainId,
  pool,                  // must be exactly right: see below
  apiUrl,
  subgraphUrl,
  assets,                // per-asset EIP-712 domains, for chains with more than one asset
  defaultAsset,
  sessionToken,          // your provider from step 3
});

await senddy.init();

The pool address is the most important line in the integration. Keys are derived from it. A wrong value doesn't throw: the user derives a different identity and sees an empty balance. Take it from Choose a chain or from @senddy/core, never by hand.

5. Deposits#

You'll usually want both flows from Move money in and out:

• Already in the wallet: senddy.deposit(amount, { token }). One signature, no gas.
• "Send funds to this address": a one-time address for new users. Your server needs a route that receives the deposit request, checks the user's signature against the token's EIP-712 domain, and relays it. Keep that check: it's what stops your route being used as an open relay.

If you adapt an existing deposit route to another chain, make sure the EIP-712 domain uses that chain's ID. A hardcoded chain ID rejects every valid deposit.

6. Content Security Policy#

connect-src needs your instance's origins. For Robinhood Chain:

https://api-rh.senddy.com  wss://api-rh.senddy.com
https://api.goldsky.com

plus your RPC provider and your login provider.

Production checklist#