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Prediction submission endpoints are write operations that interact directly with the blockchain. You must have:
  1. A funded wallet with ETH on BASE network
  2. Sufficient ETH for gas fees + stake amount
  3. A Web3 provider configured (MetaMask, WalletConnect, etc.)
The API does not submit transactions on your behalf. Use Web3 libraries to interact with the smart contracts.

​
Submit a Prediction

To submit a prediction, you must interact directly with the EnhancedPredictionMarket contract.

​
Contract Method

function submitPrediction(
  uint256 marketId,
  string memory predictedText
) external payable
​
marketId
uint256
required
The ID of the market to submit a prediction for
​
predictedText
string
required
Your predicted text (what you think the actor will say)
​
msg.value
uint256
required
Stake amount in wei (sent as transaction value)

​
Using Web3.js

JavaScript
import { ethers } from 'ethers';

// Contract ABI (simplified)
const marketABI = [
  "function submitPrediction(uint256 marketId, string memory predictedText) external payable"
];

// Connect to contract
const provider = new ethers.BrowserProvider(window.ethereum);
const signer = await provider.getSigner();
const marketContract = new ethers.Contract(
  '0x6b67cb0daaf78f63bd11195df0fd9ffe4361b93c', // Contract address
  marketABI,
  signer
);

// Submit prediction
const tx = await marketContract.submitPrediction(
  1, // marketId
  "Mars is the future of humanity", // predictedText
  { value: ethers.parseEther("0.1") } // 0.1 ETH stake
);

// Wait for confirmation
const receipt = await tx.wait();
console.log('Prediction submitted:', receipt.transactionHash);

​
Using Python (web3.py)

Python
from web3 import Web3
import os

# Connect to BASE Sepolia
w3 = Web3(Web3.HTTPProvider('https://sepolia.base.org'))

# Load contract
market_address = '0x6b67cb0daaf78f63bd11195df0fd9ffe4361b93c'
market_abi = [...] # Load from contract artifacts
market_contract = w3.eth.contract(address=market_address, abi=market_abi)

# Build transaction
account = w3.eth.account.from_key(os.environ['PRIVATE_KEY'])
tx = market_contract.functions.submitPrediction(
    1,  # market_id
    "Mars is the future of humanity"  # predicted_text
).build_transaction({
    'from': account.address,
    'value': w3.to_wei(0.1, 'ether'),  # 0.1 ETH stake
    'gas': 200000,
    'gasPrice': w3.eth.gas_price,
    'nonce': w3.eth.get_transaction_count(account.address)
})

# Sign and send
signed_tx = account.sign_transaction(tx)
tx_hash = w3.eth.send_raw_transaction(signed_tx.rawTransaction)
receipt = w3.eth.wait_for_transaction_receipt(tx_hash)
print(f'Prediction submitted: {receipt.transactionHash.hex()}')

​
Place a Bet

Bet on an existing prediction submission.

​
Contract Method

function placeBet(
  uint256 marketId,
  uint256 submissionId
) external payable
​
marketId
uint256
required
The market ID
​
submissionId
uint256
required
The submission ID to bet on (0-indexed)
​
msg.value
uint256
required
Bet amount in wei

​
Using Web3.js

JavaScript
import { ethers } from 'ethers';

const marketABI = [
  "function placeBet(uint256 marketId, uint256 submissionId) external payable"
];

const provider = new ethers.BrowserProvider(window.ethereum);
const signer = await provider.getSigner();
const marketContract = new ethers.Contract(
  '0x6b67cb0daaf78f63bd11195df0fd9ffe4361b93c',
  marketABI,
  signer
);

// Place bet
const tx = await marketContract.placeBet(
  1,  // marketId
  0,  // submissionId
  { value: ethers.parseEther("0.05") } // 0.05 ETH bet
);

const receipt = await tx.wait();
console.log('Bet placed:', receipt.transactionHash);

​
Query Your Submissions

Fetch submissions made by a specific address from the blockchain.
JavaScript
// Listen for SubmissionCreated events filtered by creator
const filter = marketContract.filters.SubmissionCreated(
  null,  // marketId (null = all markets)
  null,  // submissionId
  myAddress  // creator filter
);

const events = await marketContract.queryFilter(filter);

const mySubmissions = events.map(event => ({
  marketId: event.args.marketId,
  submissionId: event.args.submissionId,
  predictedText: event.args.predictedText,
  stake: ethers.formatEther(event.args.stake),
  blockNumber: event.blockNumber
}));

console.log('My submissions:', mySubmissions);

​
Query Your Bets

Fetch bets placed by a specific address.
JavaScript
// Listen for BetPlaced events filtered by bettor
const filter = marketContract.filters.BetPlaced(
  null,  // marketId
  null,  // submissionId
  myAddress  // bettor filter
);

const events = await marketContract.queryFilter(filter);

const myBets = events.map(event => ({
  marketId: event.args.marketId,
  submissionId: event.args.submissionId,
  amount: ethers.formatEther(event.args.amount),
  blockNumber: event.blockNumber
}));

console.log('My bets:', myBets);

​
Contract Events

The EnhancedPredictionMarket contract emits these events:

​
SubmissionCreated

event SubmissionCreated(
  uint256 indexed marketId,
  uint256 indexed submissionId,
  address indexed creator,
  string predictedText,
  uint256 stake
);

​
BetPlaced

event BetPlaced(
  uint256 indexed marketId,
  uint256 indexed submissionId,
  address indexed bettor,
  uint256 amount
);

​
MarketResolved

event MarketResolved(
  uint256 indexed marketId,
  uint256 indexed winningSubmissionId,
  string actualText
);

​
Get Contract ABI

Retrieve the contract ABI for direct integration.
cURL
curl https://proteus-production-6213.up.railway.app/api/contract-abi/EnhancedPredictionMarket
​
contract_name
string
required
Contract name: EnhancedPredictionMarket, ActorRegistry, DecentralizedOracle, or PayoutManager

​
Response

[
  {
    "inputs": [
      {"internalType": "uint256", "name": "marketId", "type": "uint256"},
      {"internalType": "string", "name": "predictedText", "type": "string"}
    ],
    "name": "submitPrediction",
    "outputs": [],
    "stateMutability": "payable",
    "type": "function"
  }
]

​
Requirements and Limits

​
Minimum Stake

  • Prediction submission: 0.01 ETH minimum
  • Bet placement: 0.001 ETH minimum

​
Gas Estimates

OperationEstimated Gas
Submit prediction~150,000
Place bet~80,000
Market creation~300,000

​
Market Timing

  • Cannot submit predictions after market end_time
  • Cannot place bets after market closes
  • Must wait for market resolution to claim winnings

​
Error Handling

Common contract revert reasons:
JavaScript
try {
  const tx = await marketContract.submitPrediction(marketId, text, { value });
  await tx.wait();
} catch (error) {
  if (error.message.includes('Market has ended')) {
    console.error('Market is closed for submissions');
  } else if (error.message.includes('Insufficient stake')) {
    console.error('Stake amount too low (min 0.01 ETH)');
  } else if (error.message.includes('Market does not exist')) {
    console.error('Invalid market ID');
  } else {
    console.error('Transaction failed:', error);
  }
}

​
Testing on Sepolia

Before deploying to mainnet, test your integration on BASE Sepolia testnet:
  • Contract: 0x6b67cb0daaf78f63bd11195df0fd9ffe4361b93c
  • RPC: https://sepolia.base.org
  • Faucet: BASE Sepolia Faucet

​
Best Practices

  1. Estimate gas before sending transactions
  2. Check market status before submitting predictions
  3. Validate user input (min/max stake amounts)
  4. Handle transaction failures gracefully
  5. Display transaction confirmations to users
  6. Cache contract ABI client-side to reduce API calls

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