# Universal Router Overview (/docs/protocols/universal-router/overview)

Learn how Uniswap Universal Router composes v2, v3, and v4 swaps with Permit2-based approvals in one transaction.

The `UniversalRouter` is an ETH and ERC20 swap router that aggregates trades across Uniswap v2, v3, and v4. It is unowned and non-upgradeable.

Its command-based architecture supports:

* Splitting and interleaving of Uniswap v2/v3/v4 swaps
* Partial fills of trades
* Wrapping and unwrapping of ETH (via WETH)
* Time-bound, signature-controlled token approvals using [Permit2](/docs/protocols/permit2/overview)
* v3 and v4 position manager interactions (e.g., permit, liquidity modification, pool initialization)
* Sub-plan execution and balance checks

Transactions are encoded as a sequence of byte-sized commands, each with structured inputs. These commands can be chained in one transaction to express custom workflows, including multi-hop swaps and liquidity migration from v3 to v4.

## How It Works
You call `execute(...)` with a `commands` byte string and a parallel `inputs` array. The router processes each command in order and routes execution to the corresponding module. This lets you combine swap, payment, approval, and position-manager actions without splitting logic across multiple transactions.

## Permit2 Integration
`UniversalRouter` integrates with `Permit2`, so token transfer permissions can be provided by signature. This reduces repeated approval flows and enables more composable routing plans.

See [Permit2 documentation](/docs/protocols/permit2/overview) for allowance and signature-transfer patterns.

## FAQ
<details>
  <summary>
    How does Universal Router command encoding work?
  </summary>

    You call `execute(commands, inputs)`, optionally with a `deadline`. The `commands` argument is a byte string where each byte is one operation, and `inputs` is a parallel array holding the ABI-encoded parameters for each command. The router walks the command stream in order and dispatches each byte to its module, so a single transaction can chain swaps across v2, v3, and v4, Permit2 permits, ETH wrapping, payments, and position-manager calls. The low 7 bits of each byte select the command, and the high bit is an allow-revert flag.

    See [Universal Router Commands](/docs/protocols/universal-router/concepts/commands) for the full command table.
</details>

<details>
  <summary>
    How is Universal Router different from SwapRouter?
  </summary>

    `SwapRouter` (SwapRouter02) exposed fixed functions tightly coupled to v2 and v3, so each call ran a scripted sequence. Universal Router is command-based: the caller composes an arbitrary ordered list of operations, so it aggregates v2, v3, and v4 swaps, Permit2 approvals, ETH wrapping, and position-manager actions in one transaction, and it supports splitting, interleaving, and partial fills. It is unowned and non-upgradeable. New integrations should target Universal Router rather than the legacy `SwapRouter`.
</details>

<details>
  <summary>
    Which Universal Router address should I use for each chain?
  </summary>

    Universal Router is deployed at a different address on each chain and per router version, so do not hardcode a single address. The current per-chain addresses are published in [Supported Chains & Tokens](/docs/trading/swapping-api/supported-chains#supported-chains-for-swapping), and the canonical source of truth is maintained in the [universal-router-sdk constants](https://github.com/Uniswap/sdks/blob/main/sdks/universal-router-sdk/src/utils/constants.ts) on GitHub. Whitelist the address for the specific chain and version you integrate.
</details>

<details>
  <summary>
    How do I enable partial fills with Universal Router?
  </summary>

    Set the high bit (`0x80`) on a command byte to mark it allow-revert. If that command fails, the rest of the transaction still executes, which is how partial fills work:

    ```solidity
    command = 0x80 | 0x00; // V3_SWAP_EXACT_IN with allow-revert
    ```

    When you use allow-revert, include a cleanup command such as `SWEEP` so no funds are stranded in the router.
</details>

<details>
  <summary>
    Do I need Permit2 to use Universal Router?
  </summary>

    Universal Router pulls a user's ERC-20 tokens through Permit2, so the user first approves the Permit2 contract once per token and then authorizes the router by signature. Native ETH does not require Permit2. See the [Permit2 documentation](/docs/protocols/permit2/overview) for allowance and signature-transfer patterns.
</details>

## Where to Go Next
* Review command encoding in [Universal Router Commands](/docs/protocols/universal-router/concepts/commands)
* Review token approval patterns in [Permit2](/docs/protocols/permit2/overview)
* Review [UniversalRouter GitHub Repository](https://github.com/Uniswap/universal-router)