# pezkuwi_sdk_docs::reference_docs::metadata - Rust
Learn about metadata, the main means through which an upgradeable runtime communicates its properties to the outside world.

## Module metadata

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Learn about metadata, the main means through which an upgradeable runtime communicates its properties to the outside world.

## §Metadata

The existence of metadata in pezkuwi-sdk goes back to the (forkless) upgrade-ability of all Bizinikiwi-based blockchains, which is achieved through `crate::reference_docs::wasm_meta_protocol`. You can learn more about the details of how to deal with these upgrades in `crate::reference_docs::frame_runtime_upgrades_and_migrations`.

Another consequence of upgrade-ability is that as a UI, wallet, or generally an offchain entity, it is hard to know the types internal to the runtime, specifically in light of the fact that they can change at any point in time.

This is why all Bizinikiwi-based runtimes must expose a [`pezsp_api::Metadata`] api, which mandates the runtime to return a description of itself. The return type of this api is `Vec<u8>`, meaning that it is up to the runtime developer to decide on the format of this.

All `crate::pezkuwi_sdk::frame_runtime` based runtimes expose a specific metadata language, maintained in https://github.com/paritytech/frame-metadata which is adopted in the Pezkuwi ecosystem.

### §Metadata Explorers:

A few noteworthy tools that inspect the (FRAME-based) metadata of a chain:

- https://wiki.network.pezkuwichain.io/docs/metadata
- https://paritytech.github.io/subxt-explorer/