Deploying smart contracts

C12 testnet EVM uses chain id 12121. Gas is paid in the mapped native denom (uc12 / ac12 extended representation in genesis). The IC12 precompile is not deployed — it is a static native address for read-only calls.

Foundry

precompiles/c12/foundry/foundry.toml (chain repo):

[profile.default]
solc_version = "0.8.24"
optimizer = false

[rpc_endpoints]
devnet = "http://127.0.0.1:8545"

Add testnet endpoint:

[rpc_endpoints]
c12_testnet = "https://evm.testnet.carbon12.network"

Deploy:

forge create src/MyContract.sol:MyContract \
  --rpc-url https://evm.testnet.carbon12.network \
  --private-key $DEPLOYER_KEY \
  --chain-id 12121

Hardhat

hardhat.config.ts (minimal):

import { HardhatUserConfig } from "hardhat/config";

const config: HardhatUserConfig = {
  solidity: "0.8.24",
  networks: {
    c12_testnet: {
      url: "https://evm.testnet.carbon12.network",
      chainId: 12121,
      accounts: process.env.DEPLOYER_KEY ? [process.env.DEPLOYER_KEY] : [],
    },
  },
};

export default config;

Interact with deployed contracts

Use ethers/viem with the testnet RPC. For native record reads, call the precompile interface — no constructor deployment.

import "./IC12.sol";

contract Reader {
    IC12 constant C12 = IC12(0x0000000000000000000000000000000000000C12);

    function head(string calldata eventId) external view returns (string memory, uint8, uint32) {
        return C12.head(eventId);
    }
}

Interface source: precompiles/c12/IC12.sol.

Precompile gas (fixed)

From precompiles/c12/precompile.go / ADR-0015:

Method	Gas
head	3000
record, aggregate	10000
claimState, checkingState	3000
reputation	2000

Reading native records from EVM

Supported via IC12 only:

• record(recordId) → protobuf-encoded bytes
• aggregate(domain, subject, periodType, periodStart) → protobuf-encoded roll-up
• checkingState(recordId), claimState(eventId, purposeId), reputation(participantId, role)

There is no generic write precompile — writes remain Cosmos Msg* transactions.

Fees & gas

• Comet minimum-gas-prices: 0.001uc12 on new nodes
• EVM module uses cosmos-evm + feemarket — effective gas price follows node app.toml / feemarket params

Fund deployer keys via faucet (testnet only, no monetary value).

Verification

Explorer bytecode verification is not yet available — see Verifying contracts.