> ## Documentation Index > Fetch the complete documentation index at: https://developers.paxoslabs.com/llms.txt > Use this file to discover all available pages before exploring further. # Concepts > Key ideas to understand before integrating with Amplify smart contracts directly If you're new to on-chain integrations, read through these before diving into the [guides](/v0.5.2/intro/products/earn/developers/guides/direct-contract/index). ## Accounts & Yield Types * **Account** — An on-chain contract that issues ERC-20 shares representing a position in an underlying strategy. * **Yield Type** — Logical grouping of accounts with similar mandates (`CORE`, `TREASURY`, `FRONTIER`). Used as a filter when [discovering accounts](/v0.5.2/intro/products/earn/developers/guides/direct-contract/vault-queries/vault-discovery) via the GraphQL API. * **Want Asset** — The token users receive when withdrawing from an account; often different from the deposit token. ### Account Discovery All contract addresses are available via the GraphQL API at `POST https://api.paxoslabs.com/graphql`. See [Setup & Prerequisites](/v0.5.2/intro/products/earn/developers/guides/direct-contract/setup#obtaining-contract-addresses) for the full query and response format. ## What is a Smart Contract? A smart contract is a program deployed on the Ethereum blockchain. Once deployed, anyone can call its functions by sending a **transaction** (for writes) or making a **call** (for reads). You interact with contracts using their **address** (like a URL) and their **ABI** (like an API schema). ## What is an ABI? An **Application Binary Interface (ABI)** is a JSON description of a contract's functions — their names, parameter types, and return types. Think of it as an OpenAPI/Swagger spec for a smart contract. Your code uses the ABI to encode function calls into the binary format the blockchain expects. ## What is a Token Approval? ERC-20 tokens (like USDC) don't allow contracts to spend your tokens by default. Before a contract can move tokens on your behalf, you must **approve** it by calling the token's `approve(spender, amount)` function. This is a safety mechanism — you explicitly opt in to each contract interaction. ## What is an EIP-2612 Permit? A **permit** is a gasless alternative to `approve` defined by [EIP-2612](https://eips.ethereum.org/EIPS/eip-2612). Instead of sending an on-chain approval transaction, you sign an off-chain message that authorizes a contract to spend your tokens. The contract verifies this signature on-chain. Not all tokens support permits — USDT notably does not. ## Shares vs. Assets * [Deposits](/v0.5.2/intro/products/earn/developers/guides/direct-contract/deposits) mint **account shares** to the recipient. Shares are ERC-20 tokens representing your proportional ownership of the account's assets. * [Withdrawals](/v0.5.2/intro/products/earn/developers/guides/direct-contract/withdrawals) burn shares and return the **want asset** (e.g., USDC). The want asset may differ from the token you deposited. * The exchange rate between shares and the underlying tokens changes over time as the account earns yield. * All on-chain values are in **base units** (e.g., 1 USDC = `1000000` with 6 decimals). ## Slippage Controls When depositing, the `minimumMint` parameter protects you from receiving fewer shares than expected due to exchange rate changes between when you prepare and when your transaction is mined. This is expressed as a minimum number of shares to receive — if the account would mint fewer, the transaction reverts. A common default is 0.5% (50 basis points) below the expected share amount. ## Withdrawals * Withdrawals are **order-based**, not instant. You submit an order to the [WithdrawQueue](/v0.5.2/intro/products/earn/developers/guides/direct-contract/withdrawals) and the account operator fulfills it (typically within 24 hours). * You must **approve** your account shares to the WithdrawQueue before submitting an order. * Once fulfilled, the want asset is sent directly to the address that submitted the order. * Pending orders can be [cancelled](/v0.5.2/intro/products/earn/developers/guides/direct-contract/cancellations) to recover your locked account shares. ## Execution Responsibilities When integrating directly with smart contracts, your application is responsible for: * **Building calldata** — ABI-encoding function calls with the correct parameters * **Submitting transactions** — Signing and broadcasting via your [chosen Ethereum library](/v0.5.2/intro/products/earn/developers/guides/direct-contract/setup#code-examples) * **Handling gas** — Estimating gas limits and setting appropriate gas prices * **Error handling** — Parsing revert reasons from failed transactions *** ## Contract Architecture Amplify accounts are built on the [Nucleus BoringVault](https://github.com/paxoslabs/nucleus-boring-vault) framework — an open-source, audited account architecture. You can browse the full Solidity source, deployment configs, and audit reports in the [GitHub repository](https://github.com/paxoslabs/nucleus-boring-vault). Three contracts handle user-facing operations: | Contract | Role | What You Call It For | | ---------------------------- | -------------------------- | -------------------------------------------------- | | **DistributorCodeDepositor** | Deposit entry point | Depositing tokens into the account | | **WithdrawQueue** | Withdrawal order manager | Submitting and cancelling withdrawal orders | | **BoringVault** | ERC-20 account share token | Approving shares for withdrawal, checking balances | ### Lifecycle You approve the deposit token (e.g., USDC) to the DistributorCodeDepositor, then call [`deposit()`](/v0.5.2/intro/products/earn/developers/guides/direct-contract/deposits). The account mints shares to your address. You approve your account shares to the WithdrawQueue, then call [`submitOrder()`](/v0.5.2/intro/products/earn/developers/guides/direct-contract/withdrawals). The account operator fulfills your order (typically within 24 hours) and sends the want asset to your address. If your withdrawal is still pending, you can call [`cancelOrder()`](/v0.5.2/intro/products/earn/developers/guides/direct-contract/cancellations) on the WithdrawQueue. Your locked account shares are returned to you. *** ## Glossary | Term | Definition | | ---------------------- | ---------------------------------------------------------------------------------------------------------- | | **ABI** | Application Binary Interface — a JSON schema that describes how to encode/decode calls to a contract | | **Approval** | An on-chain transaction granting a contract permission to transfer your tokens | | **Basis points (bps)** | A unit of measurement where 1 bps = 0.01%. 50 bps = 0.5%, 100 bps = 1%. | | **EIP-2612 Permit** | An off-chain signature that authorizes token spending without an on-chain approval transaction | | **ERC-20** | The standard interface for fungible tokens (USDC, USDT, etc.) | | **Gas** | The fee paid in ETH to execute a transaction on Ethereum | | **Nonce** | A sequential counter that prevents transaction replay | | **RPC** | Remote Procedure Call — the API protocol used to communicate with an Ethereum node | | **Slippage** | The difference between the expected and actual exchange rate. Controlled via `minimumMint`. | | **Account shares** | ERC-20 tokens representing your deposit in the account; their value appreciates as the account earns yield | | **Want asset** | The token you want to receive when withdrawing (e.g., USDC) | | **WithdrawQueue** | The contract that manages withdrawal orders as an ordered queue |