Flow Playground

Flow Client Library (FCL)

Introducing @onflow/fcl

Flow Client Library (FCL) enables applications to easily integrate with all FCL-compatible wallets and other services (e.g. (Comming Soon) profiles, private information, notifications). This offers developers a strong foundation to compose their apps with existing building blocks. It’s currently supported for browser applications, and will be extended to other platforms.

With FCL, you can:

  • Integrate all compatible wallets without any custom code or code injection
  • Authenticate users
  • Query the Flow Blockchain
  • Send transactions (e.g. initializing resources, sending assets, purchasing, etc.)
  • Sign transactions through wallet integration avoiding key management

With FCL, you will eventually be able to:

  • Personally sign data via FCL Compatible Wallets
  • Request Additional User info like Emails

While it would be possible to create a Flow wallet as a browser plugin, we specifically created @onflow/fcl so that web-based dapps don’t have to depend on browser plugins. @onflow/fcl is able to connect browser-based dapps to a wallet service, or a wallet installed on your phone or running on your local computer without introducing the security risks that can come from installing a browser plugin.


  • Last Updated: Mar 2nd 2021
  • Stable: Yes
  • Risk of Breaking Change: Low

The things that exists probably won't be changing much externally, we will be adding new functionality in the near future.

Wallet Discovery

FCL also eliminates the need for dapp developers to write code to integrate their user's preferred wallet into their application. Instead,@onflow/fcl uses a secure discovery protocol that wallets can implement to connect to @onflow/fcl. The end result is dapps using @onflow/fcl automatically integrate all compatible wallets without their developers needing to write any custom code!

Limitless Development

@onflow/fcl enables cross-platform dapps. By not depending on JavaScript injection as a mechanism for connecting dapps with wallets, native desktop dapps and mobile dapps can connect to the same wallet software as browser dapps.

Getting Started with FCL

To use the Flow JavaScript SDK in your application, install using yarn or npm

npm i -S @onflow/fcl @onflow/types

Learn to use @onflow/fcl: Flow App Quickstart


Please note, that some code provided - e.g. Object.fromEntries - will require Node version v12.0.0 or higher.