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#7 in #subxt

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subxt · build Latest Version Documentation

Subxt is a library for interacting with Substrate 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.


Take a look in the examples folder or the examples folder for various smaller or larger subxt usage examples, or read the guide to learn more.

Downloading metadata from a Substrate node

Use the subxt-cli tool to download the metadata for your target runtime from a node.

  1. Install:
cargo install subxt-cli
  1. Save the encoded metadata to a file:
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.

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:

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 CLI for interacting with Wasm smart contracts.
  • xcm-cli CLI for submitting XCM messages.
  • phala-pherry The relayer between Phala blockchain and the off-chain Secure workers.
  • crunch CLI to claim staking rewards in batch every Era or X hours for substrate-based chains.
  • interbtc-clients Client implementations for the interBTC parachain; notably the Vault / Relayer and Oracle.
  • tidext Tidechain client with Stronghold signer.
  • staking-miner-v2 Submit NPos election solutions and get rewards.
  • polkadot-introspector Tools for monitoring Polkadot nodes.
  • ink! Smart contract language that uses subxt for allowing developers to conduct End-to-End testing of their contracts.
  • Chainflip A decentralised exchange for native cross-chain swaps.


substrate-api-client provides similar functionality.


The entire code within this repository is dual licensed under the GPL-3.0 or Apache-2.0 licenses. See the LICENSE file for more details.

Please contact us if you have questions about the licensing of our products.


Subxt macro for generating Substrate runtime interfaces.


~423K SLoC