Private DeFi End to End

The anonymizer contract pages cover the Cairo side. This page covers the other half: how a dapp actually reaches that contract through the Starknet Wallet API, without ever touching a viewing key.

Requires starknet@^10.4.0 and a wallet supporting Wallet API 0.10.3.

The two actions

A private DeFi call is one STRK20 transaction carrying two actions:

A transfer with the literal amount "OPEN" — this creates an open note, the slot your helper's output gets credited into. Its amount is only known after the helper runs on-chain.
An invoke naming your helper contract and its calldata.

The wallet resolves two placeholders inside the invoke calldata:

Placeholder	Resolves to
`${openNoteIds[N]}`	The id of the Nth open note in this transaction
`${poolAddress}`	The privacy pool contract address

That indirection is what lets you reference a note that does not exist yet at the time you build the calldata.

A private swap

import type { STRK20_ACTION } from "@starknet-io/types-js"

const actions: STRK20_ACTION[] = [
  // 1. Open the note the swap output will be credited into.
  { type: "transfer", token: tokenOut, amount: "OPEN", recipient: userAddress },

  // 2. Call the helper. ${openNoteIds[0]} is the note opened above.
  {
    type: "invoke",
    contract: swapHelperAddress,
    calldata: [tokenIn, tokenOut, amountIn, "${openNoteIds[0]}"],
  },
]

const { transaction_hash } = await account.strk20InvokeTransaction(actions)

The pool withdraws amountIn to your helper, calls its privacy_invoke entry point, and credits the returned OpenNoteDeposit into the open note — atomically. Observers see pool → helper → AMM → helper. They do not see who initiated it.

Match the calldata order to your helper's privacy_invoke signature; the pool deserializes it directly into that function's parameters.

Dry-run first

strk20PrepareInvoke builds and proves the same actions without submitting, which is the cheapest way to catch a calldata-shape mistake:

const prepared = await account.strk20PrepareInvoke(actions, true) // simulate

Show the shielded balance

Reading private balances is a wallet call too — no viewing key in your app:

const balances = await account.strk20Balances([tokenIn, tokenOut])
// [{ token, balance }, ...]

What stays public