# Working on-Chain

- [Credentials Verification Service](/developer-guide/working-on-chain/credentials-verification-service.md)
- [Contracts](/developer-guide/working-on-chain/contracts.md)
- [IFeeEscrow](/developer-guide/working-on-chain/contracts/ifeeescrow.md)
- [IVerificationOracle](/developer-guide/working-on-chain/contracts/iverificationoracle.md)
