> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cow.bleu.builders/llms.txt
> Use this file to discover all available pages before exploring further.

# Merkle Root Orders

> Efficiently batch multiple programmatic orders using merkle trees for reduced gas costs.

# Merkle Root Orders

## Key Concept

Merkle root orders enable efficient batching of multiple programmatic orders through a single on-chain transaction. Rather than executing individual `create()` calls for each order, you establish one merkle root that authorizes all orders simultaneously -- dramatically reducing gas costs.

## Core Process

The implementation follows four main steps:

1. **Collect orders** as `ConditionalOrderParams` structures
2. **Construct merkle tree** where each leaf uses double hashing:
   ```solidity theme={null}
   keccak256(bytes.concat(keccak256(abi.encode(params))))
   ```
3. **Register root on-chain** via `ComposableCoW.setRoot()`
4. **Validate orders** by providing merkle proofs alongside order parameters

## Critical Technical Details

### Double Hashing Requirement

The system employs double hashing to prevent second preimage attacks. This is essential -- always apply the following for leaf calculations:

```solidity theme={null}
keccak256(bytes.concat(keccak256(abi.encode(params))))
```

### Proof Verification

When retrieving tradeable orders, you must supply the merkle proof. An empty proof array signals a single order rather than a merkle-authorized order.

## Gas Efficiency

The overhead for `setRoot()` remains relatively constant regardless of tree size. For example:

| Method                  | Gas for 50 orders |
| ----------------------- | ----------------- |
| Individual `create()`   | \~2.5M gas        |
| Merkle root `setRoot()` | \~55k gas         |

This represents approximately a **45x improvement**.

## Context Storage

Use `setRootWithContext()` to store supplementary data (like timestamps) on-chain. For TWAP orders where `t0=0`, this allows automatic reading of start times from stored context.

## Management Flexibility

* Updating orders requires recalculating the merkle root and invoking `setRoot()` again
* Setting the root to `bytes32(0)` invalidates all prior authorizations