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§Offchain Worker Example Pallet

The Offchain Worker Example: A simple pallet demonstrating concepts, APIs and structures common to most offchain workers.

Run cargo doc --package pallet-example-offchain-worker --open to view this module’s documentation.

This pallet serves as an example showcasing Substrate off-chain worker and is not meant to be used in production.


In this example we are going to build a very simplistic, naive and definitely NOT production-ready oracle for BTC/USD price. Offchain Worker (OCW) will be triggered after every block, fetch the current price and prepare either signed or unsigned transaction to feed the result back on chain. The on-chain logic will simply aggregate the results and store last 64 values to compute the average price. Additional logic in OCW is put in place to prevent spamming the network with both signed and unsigned transactions, and custom UnsignedValidator makes sure that there is only one unsigned transaction floating in the network.



  • Based on the above KeyTypeId we need to generate a pallet-specific crypto type wrappers. We can use from supported crypto kinds (sr25519, ed25519 and ecdsa) and augment the types with this pallet-specific identifier.
  • The pallet module in each FRAME pallet hosts the most important items needed to construct this pallet.


  • Payload used by this example crate to hold price data required to submit a transaction.


  • Defines application identifier for crypto keys of this module.