# subxt ·  [](https://crates.io/crates/subxt) [](https://docs.rs/subxt)
Subxt is a library for interacting with [Substrate](https://github.com/paritytech/polkadot-sdk) based nodes in Rust and WebAssembly. It can:
- Submit Extrinsics (this is where the name comes from).
- Subscribe to blocks, reading the extrinsics and associated events from them.
- Read and iterate over storage values.
- Read constants and custom values from the metadata.
- Call runtime APIs, returning the results.
- Do all of the above via a safe, statically types interface or via a dynamic one when you need the flexibility.
- Compile to WASM and run entirely in the browser.
- Do a bunch of things in a `#[no_std]` environment via the `subxt-core` crate.
- Use a built-in light client (`smoldot`) to interact with chains.
## Usage
Take a look in the [examples](./subxt/examples) folder or the [examples](./examples) folder for various smaller or
larger `subxt` usage examples, or [read the guide](https://docs.rs/subxt/latest/subxt/book/index.html) to learn more.
### Downloading metadata from a Substrate node
Use the [`subxt-cli`](./cli) tool to download the metadata for your target runtime from a node.
1. Install:
```bash
cargo install subxt-cli
```
2. Save the encoded metadata to a file:
```bash
subxt metadata -f bytes > metadata.scale
```
This defaults to querying the metadata of a locally running node on the default `http://localhost:9933/`. If querying
a different node then the `metadata` command accepts a `--url` argument.
## Subxt Documentation
For more details regarding utilizing subxt, please visit the [documentation](https://docs.rs/subxt/latest/subxt/).
## Integration Testing
Most tests require a running substrate node to communicate with. This is done by spawning an instance of the
substrate node per test. It requires an up-to-date `substrate` executable on your path.
This can be installed from source via cargo:
```bash
cargo install --git https://github.com/paritytech/polkadot-sdk staging-node-cli --force
```
## Real world usage
Please add your project to this list via a PR.
- [cargo-contract](https://github.com/paritytech/cargo-contract/) CLI for interacting with Wasm smart contracts.
- [xcm-cli](https://github.com/ascjones/xcm-cli) CLI for submitting XCM messages.
- [phala-pherry](https://github.com/Phala-Network/phala-blockchain/tree/master/standalone/pherry) The relayer between Phala blockchain and the off-chain Secure workers.
- [crunch](https://github.com/turboflakes/crunch) CLI to claim staking rewards in batch every Era or X hours for substrate-based chains.
- [interbtc-clients](https://github.com/interlay/interbtc-clients) Client implementations for the interBTC parachain; notably the Vault / Relayer and Oracle.
- [tidext](https://github.com/tidelabs/tidext) Tidechain client with Stronghold signer.
- [staking-miner-v2](https://github.com/paritytech/staking-miner-v2) Submit NPos election solutions and get rewards.
- [polkadot-introspector](https://github.com/paritytech/polkadot-introspector) Tools for monitoring Polkadot nodes.
- [ink!](https://github.com/paritytech/ink) Smart contract language that uses `subxt` for allowing developers to conduct [End-to-End testing](https://use.ink/basics/contract-testing/end-to-end-e2e-testing) of their contracts.
- [Chainflip](https://github.com/chainflip-io/chainflip-backend) A decentralised exchange for native cross-chain swaps.
- [Hyperbridge](https://github.com/polytope-labs/hyperbridge) A hyperscalable coprocessor for verifiable cross-chain interoperability.
- [pop CLI](https://github.com/r0gue-io/pop-cli) The all-in-one tool for Polkadot development.
**Alternatives**
[substrate-api-client](https://github.com/scs/substrate-api-client) provides similar functionality.
#### License
The entire code within this repository is dual licensed under the _GPL-3.0_ or _Apache-2.0_ licenses. See [the LICENSE](./LICENSE) file for more details.
Please <a href="https://www.parity.io/contact/">contact us</a> if you have questions about the licensing of our products.