# Cross-Consensus Query Language (XCQ)

**URL:** https://forum.polkadot.network/t/cross-consensus-query-language-xcq/7583
**Category:** Tech Talk
**Created:** [April 26, 2024, 4:39am UTC](https://forum.polkadot.network/t/cross-consensus-query-language-xcq/7583 "2024-04-26T04:39:17Z")
**Posts on this page:** 1
**Showing post:** 24

<div class="post-metadata">

### Author: ![indirection42](https://dub1.discourse-cdn.com/flex005/user_avatar/forum.polkadot.network/indirection42/32/4894_2.png) [@indirection42](https://forum.polkadot.network/u/indirection42)
#### Post date: [August 4, 2025, 12:23pm UTC](https://forum.polkadot.network/t/cross-consensus-query-language-xcq/7583/24 "2025-08-04T12:23:37Z")

</div>

We’ve built a simple [swap demo](https://open-web3-stack.github.io/pvq-sdk/swap/) showcases how PVQ can facilitate the development of multi-chain Dapps. It has the following core functions:

- List Liquidity Pools: Displays the available token pair pools on the selected chain.

- Get Pool Reserves: Shows the current liquidity reserves for a selected pool.

- Get Swap Price: Show price quote for swapping a specific amount of one token for another.

 ![截屏2025-08-04 20.23.16](https://europe1.discourse-cdn.com/flex005/uploads/polkadot2/original/2X/0/0158b5e11a577caf23bdcb3214af933fb9fb949f.png)

**The main takeaway is that the demo works seamlessly with both Acala and AssetHub, using the exact same front-end logic despite the DEX implementations on these chains being entirely different:**

- Acala: Uses its own custom `module-dex` pallet.

- AssetHub: Uses the `AssetConversion` pallet.

### How It Works

#### Front-end side

From the client’s perspective, the process is simple:

- Check for Extension: The UI first checks if the connected chain (Acala or AssetHub) implements the `swap` extension.

- Construct PVQ program query arguments: If the extension is available, the UI constructs its query with the required arguments (e.g., token pair, amount to swap).

- Call PVQ program Entrypoints: The UI sends the query to the entrypoints of the PVQ program.

The front-end code is completely agnostic of whether it’s talking to Acala’s DEX pallet or AssetHub’s AssetConversion pallet.

#### Runtime side

The heavy lifting is done at the runtime side, which is tailored for each chain. We implement [swap extension](https://github.com/open-web3-stack/PVQ/blob/61950049b9c668f0db4b9fd059f5abb11d3b65e5/pvq-extension-swap) on both Acala and AssetHub, which exposes five extension functions: `quote_price_tokens_for_exact_tokens`, `quote_price_exact_tokens_for_tokens`, `get_liquidity_pool`, `list_pools`, `asset_info`, `assets_info`.

#### PVQ Program

For the corresponding PVQ program, it only has four entrypoints. This is by design and demonstrates one of PVQ’s most powerful features: the ability to perform custom computations in PVQ program.

For example, the `list_pools` entrypoint is actually a composition of extension functions `list_pools` and `assets_info`:

```rust
#[program::entrypoint]
fn entrypoint_list_pools() -> Vec<(AssetInfo, AssetInfo)> {
    let pools = list_pools();
    let mut result = Vec::new();
    let assets_info = assets_info();
    for pool in pools {
        let asset1_info = assets_info.get(&pool.0).cloned();
        let asset2_info = assets_info.get(&pool.1).cloned();
        if let (Some(a1), Some(a2)) = (asset1_info, asset2_info) {
            result.push((a1, a2));
        }
    }
    result
}

```

#### Key Advancement

This demo is a concrete validation of the PVQ vision. We have successfully created a unified, high-level interface for a non-trivial operation (DEX interactions) across two parachains with fundamentally different runtime implementations.

For dApp developers:

- Reduced Complexity: No need to learn the low-level details of every parachain’s pallets.

- Faster Development: Write code once and deploy it across multiple chains.

- Easy Extensibility: As more chains adopt the PVQ swap extension, they will instantly work with existing UIs without requiring any front-end updates.

This advancement is a crucial step toward a more cohesive and developer-friendly Polkadot ecosystem.

#### Next Steps

We are targeting the first release of the PVQ and integrating it into the `polkadot-sdk`.

We welcome feedback, questions, and collaboration from the community. Please feel free to check out the demo and share your thoughts below.

Thank you!

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