eth_getStorageAt | Moonbase Alpha RPC Docs

Read the value from a storage slot at a given contract address on Moonbase Alpha. Essential for reading contract state directly, proxy implementation verification, and storage layout analysis.

Returns the value from a storage position at a given address on Moonbase Alpha. This provides direct access to the raw EVM storage of any smart contract, bypassing ABI encoding and public getter functions.

Why Moonbase? Build on the Moonbeam testnet for risk-free EVM dApp development and deployment testing with free testnet tokens, full EVM compatibility, XCM testing capabilities, and identical feature set to Moonbeam mainnet.

When to Use This Method

eth_getStorageAt is essential for Moonbeam developers, dApp testers, and teams validating cross-chain integrations:

Reading Private State — Access contract state variables that have no public getter, including variables marked as private or internal in Solidity
Proxy Implementation Verification — Read the implementation address from EIP-1967 proxy storage slots to verify which logic contract a proxy delegates to on EVM dApp testing, XCM integration validation, and pre-mainnet deployment verification
Storage Layout Analysis — Inspect raw storage slots for security auditing, debugging, or reverse-engineering contract behavior
State Change Monitoring — Track specific storage slot changes across blocks to monitor protocol parameters, admin roles, or balances

import { JsonRpcProvider, keccak256, toUtf8Bytes } from 'ethers';

const provider = new JsonRpcProvider('https://api-moonbase-alpha.n.dwellir.com/YOUR_API_KEY');

async function getProxyImplementation(proxyAddress) {
  // EIP-1967 implementation slot:
  // bytes32(uint256(keccak256('eip1967.proxy.implementation')) - 1)
  const EIP1967_IMPL_SLOT = '0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc';

  const value = await provider.getStorage(proxyAddress, EIP1967_IMPL_SLOT);

  // Extract the address from the 32-byte value (last 20 bytes)
  const implAddress = '0x' + value.slice(26);

  if (implAddress === '0x' + '0'.repeat(40)) {
    console.log('Not a standard EIP-1967 proxy or no implementation set');
    return null;
  }

  console.log(`Proxy: ${proxyAddress}`);
  console.log(`Implementation: ${implAddress}`);
  return implAddress;
}

// Also check the admin slot
async function getProxyAdmin(proxyAddress) {
  const EIP1967_ADMIN_SLOT = '0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103';
  const value = await provider.getStorage(proxyAddress, EIP1967_ADMIN_SLOT);
  return '0x' + value.slice(26);
}

2. Read Solidity Mapping Values

Calculate the storage slot for a mapping entry and read it:

JavaScript

import { JsonRpcProvider, keccak256, AbiCoder, zeroPadValue, toBeHex } from 'ethers';

const provider = new JsonRpcProvider('https://api-moonbase-alpha.n.dwellir.com/YOUR_API_KEY');

async function readMapping(contractAddress, mappingSlot, key) {
  // For mapping(address => uint256) at slot N:
  // slot = keccak256(abi.encode(key, N))
  const abiCoder = AbiCoder.defaultAbiCoder();
  const encoded = abiCoder.encode(
    ['address', 'uint256'],
    [key, mappingSlot]
  );
  const slot = keccak256(encoded);

  const value = await provider.getStorage(contractAddress, slot);
  return BigInt(value);
}

// Example: read an ERC-20 balance (balanceOf mapping is typically at slot 0 or 1)
const contractAddress = '0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045';
const holderAddress = '0x1234567890abcdef1234567890abcdef12345678';
const balance = await readMapping(contractAddress, 0, holderAddress);
console.log('Token balance:', balance.toString());

3. Storage Layout Inspector

Scan multiple storage slots to analyze a contract's state:

JavaScript

async function inspectStorage(provider, address, slotCount = 10) {
  console.log(`Inspecting storage for ${address} on Moonbase:`);
  console.log('─'.repeat(80));

  const results = [];
  for (let i = 0; i < slotCount; i++) {
    const value = await provider.getStorage(address, i);
    const isZero = value === '0x' + '0'.repeat(64);

    if (!isZero) {
      // Try to interpret the value
      const asNumber = BigInt(value);
      const asAddress = '0x' + value.slice(26);
      const hasAddressPattern = value.slice(2, 26) === '0'.repeat(24);

      console.log(`Slot ${i}: ${value}`);
      if (hasAddressPattern && asAddress !== '0x' + '0'.repeat(40)) {
        console.log(`  → Possible address: ${asAddress}`);
      } else {
        console.log(`  → As uint256: ${asNumber}`);
      }

      results.push({ slot: i, value, asNumber });
    }
  }

  return results;
}

Error Handling

Common errors and solutions:

Error Code	Description	Solution
-32602	Invalid params	Verify the address is a valid 20-byte hex string, position is a valid hex quantity, and block parameter is valid
-32603	Internal error	Retry with exponential backoff
-32000	Execution error	The requested block may be pruned — try `latest` or a more recent block
-32005	Rate limit exceeded	Implement caching and reduce request frequency

JavaScript

async function safeGetStorage(provider, address, slot, maxRetries = 3) {
  for (let i = 0; i < maxRetries; i++) {
    try {
      return await provider.getStorage(address, slot);
    } catch (error) {
      if (error.code === -32000) {
        // Block may be pruned — try latest
        return await provider.getStorage(address, slot, 'latest');
      }
      if (error.code === -32005) {
        await new Promise(r => setTimeout(r, Math.pow(2, i) * 1000));
        continue;
      }
      if (i === maxRetries - 1) throw error;
      await new Promise(r => setTimeout(r, Math.pow(2, i) * 1000));
    }
  }
}

eth_call — Execute a contract function call without a transaction
eth_getCode — Get the bytecode deployed at an address
eth_getBalance — Get the ETH balance of an address
eth_getBlockByNumber — Get block details for historical storage queries

eth_getStorageAt - Moonbase RPC Method

When to Use This Method

Code Examples

Common Use Cases

1. Verify Proxy Implementation Address

2. Read Solidity Mapping Values

3. Storage Layout Inspector

Error Handling

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