Schedule Service System Contract Skill

Hedera Schedule Service (HSS) System Contract

The Hedera Schedule Service system contract at 0x16b exposes functions for creating and managing scheduled transactions from within Solidity. It supports:

HIP-755: Authorizing and signing schedules from contracts
HIP-756: Scheduling native HTS token creation (createFungibleToken, createNonFungibleToken, etc.)
HIP-1215: Generalized scheduled contract calls — schedule arbitrary calls to any contract (or self) for DeFi automation, vesting, DAO operations

Quick Reference

Contract address: 0x16b

Imports:

import {HederaScheduleService} from "@hashgraph/smart-contracts/contracts/system-contracts/hedera-schedule-service/HederaScheduleService.sol";
import {IHRC1215ScheduleFacade} from "@hashgraph/smart-contracts/contracts/system-contracts/hedera-schedule-service/IHRC1215ScheduleFacade.sol";

HederaScheduleService is an abstract contract (like HederaTokenService for HTS). Inherit it to get internal helper functions that handle the low-level calls to 0x16b. HederaResponseCodes is available transitively.

Response codes: SUCCESS = 22 (HederaResponseCodes.SUCCESS). See references/api.md for full function list and Hedera response codes.

Critical: Inheritance Pattern

IHederaScheduleService is an empty interface. Functions are defined in IHRC755, IHRC756, IHRC1215 and wrapped as internal helpers in HederaScheduleService. Your contract must inherit HederaScheduleService:

contract MyScheduler is HederaScheduleService {
    error ScheduleFailed();

    function doSchedule() external {
        (int64 rc, address scheduleAddr) = scheduleCall(target, expiry, gasLimit, 0, data);
        if (rc != HederaResponseCodes.SUCCESS) revert ScheduleFailed();
    }
}

Critical: Non-Reverting Behavior (HIP-1215)

The scheduleCall, scheduleCallWithPayer, and executeCallOnPayerSignature functions do not revert. On failure they return (responseCode, address(0)). Always check:

error ScheduleFailed();

(int64 rc, address scheduleAddr) = scheduleCall(target, expiry, gasLimit, 0, data);
if (rc != HederaResponseCodes.SUCCESS || scheduleAddr == address(0)) {
    revert ScheduleFailed();
}

Capacity and Throttling (HIP-1215)

Scheduled calls are throttled per second. Use hasScheduleCapacity(expirySecond, gasLimit) before scheduling to avoid SCHEDULE_EXPIRY_IS_BUSY:

bool capacity = hasScheduleCapacity(expirySecond, gasLimit);
if (!capacity) {
    // Retry with a later expiry or different gas limit
    // See HIP-1215 findAvailableSecond() pattern for exponential backoff + jitter
}

Common Concepts

Scheduled transaction: Wraps a Hedera transaction (native HTS call or EVM contract call) for deferred execution when signature thresholds are met.
Payer: Account responsible for paying fees. With scheduleCall, the calling contract is the payer. With scheduleCallWithPayer / executeCallOnPayerSignature, a separate payer can be specified.
authorizeSchedule: Signs the schedule with the calling contract's key (ContractKey format 0.0.<ContractId>).
signSchedule: Adds protobuf-encoded signatures from EOAs or other keys.
Expiration: Schedules that fail to collect all required signatures before expirySecond are automatically removed from the network.

Usage Patterns

Schedule Native Token Creation (HIP-756)

Note: The payer must have sufficient HBAR when the schedule executes (for the token creation fee).

import {HederaScheduleService} from "@hashgraph/smart-contracts/contracts/system-contracts/hedera-schedule-service/HederaScheduleService.sol";
import {IHederaTokenService} from "@hashgraph/smart-contracts/contracts/system-contracts/hedera-token-service/IHederaTokenService.sol";

contract ScheduledTokenCreator is HederaScheduleService {
    error FailToSchedule();

    function scheduleTokenCreate(
        IHederaTokenService.HederaToken memory token,
        int64 initialSupply,
        int32 decimals,
        address payer
    ) external returns (address scheduleAddr) {
        bytes memory callData = abi.encodeCall(
            IHederaTokenService.createFungibleToken,
            (token, initialSupply, decimals)
        );
        int64 rc;
        (rc, scheduleAddr) = scheduleNative(
            address(0x167), callData, payer
        );
        if (rc != HederaResponseCodes.SUCCESS) revert FailToSchedule();
    }
}

Schedule Arbitrary Contract Call (HIP-1215)

import {HederaScheduleService} from "@hashgraph/smart-contracts/contracts/system-contracts/hedera-schedule-service/HederaScheduleService.sol";

contract Scheduler is HederaScheduleService {
    error FailToSchedule();
    event ScheduleCreated(address);

    function scheduleFutureCall(
        address target,
        uint256 expirySecond,
        uint256 gasLimit,
        bytes memory callData
    ) external returns (address scheduleAddr) {
        if (!hasScheduleCapacity(expirySecond, gasLimit)) revert FailToSchedule();

        int64 rc;
        (rc, scheduleAddr) = scheduleCall(
            target,
            expirySecond > 0 ? expirySecond : block.timestamp + 5,
            gasLimit,
            0,
            callData
        );
        if (rc != HederaResponseCodes.SUCCESS) {
            revert FailToSchedule();
        }
        emit ScheduleCreated(scheduleAddr);
    }
}

Contract Signs Schedule (HIP-755)

import {HederaScheduleService} from "@hashgraph/smart-contracts/contracts/system-contracts/hedera-schedule-service/HederaScheduleService.sol";

contract ScheduleSigner is HederaScheduleService {
    error FailToAuthorize();
    error FailToSign();

    function signAsContract(address scheduleAddr) external {
        int64 rc = authorizeSchedule(scheduleAddr);
        if (rc != HederaResponseCodes.SUCCESS) revert FailToAuthorize();
    }

    function signWithSignatureMap(address scheduleAddr, bytes memory sigMap) external {
        int64 rc = signSchedule(scheduleAddr, sigMap);
        if (rc != HederaResponseCodes.SUCCESS) revert FailToSign();
    }
}

Delete Schedule

import {HederaScheduleService} from "@hashgraph/smart-contracts/contracts/system-contracts/hedera-schedule-service/HederaScheduleService.sol";
import {IHRC1215ScheduleFacade} from "@hashgraph/smart-contracts/contracts/system-contracts/hedera-schedule-service/IHRC1215ScheduleFacade.sol";

contract ScheduleManager is HederaScheduleService {
    error FailToDeleteSchedule();

    // Option 1: Internal helper (inheriting HederaScheduleService)
    function deleteScheduleExample(address scheduleAddr) external {
        int64 rc = deleteSchedule(scheduleAddr);
        if (rc != HederaResponseCodes.SUCCESS) {
            revert FailToDeleteSchedule();
        }
    }

    // Option 2: Redirect — call deleteSchedule() on the schedule's address
    // (works for contracts and EOAs)
    function deleteScheduleProxy(address scheduleAddr) external {
        int64 rc = IHRC1215ScheduleFacade(scheduleAddr).deleteSchedule();
        if (rc != HederaResponseCodes.SUCCESS) {
            revert FailToDeleteSchedule();
        }
    }
}

Costs

Schedule transaction fees match HAPI ScheduleCreate, with a 20% markup for system contract usage.
Includes gas, storage, and consensus fees. Expired transactions incur no extra fees beyond initial scheduling/signature costs.

References

API Reference: references/api.md — Full function signatures, selectors, and usage notes
HIP-755: Schedule Service System Contract
HIP-756: Contract Scheduled Token Create
HIP-1215: Generalized Scheduled Contract Calls
Source: hedera-smart-contracts/hedera-schedule-service