> ## Documentation Index
> Fetch the complete documentation index at: https://docs.chainstack.com/llms.txt
> Use this file to discover all available pages before exploring further.

# eth_getStorageAt | Polygon

Polygon API method that returns the data stored at a specific storage slot within a smart contract. It can help developers to read a smart contract's internal state, like user data or balances, to inform decisions and build more advanced applications that interact with smart contracts on the blockchain.

<Note>
  When called against a block older than the latest \~128 blocks, this method is treated as an archive request (2 RUs instead of 1 RU). See [request units](/docs/request-units#archive-state-methods).
</Note>

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## Parameters

* `address` — the address of the smart contract to query
* `quantity` — the index of the storage position to retrieve the data from
* `quantity or tag` — the integer of a block encoded as hexadecimal or the string with:

  * `latest` — the most recent block in the blockchain and the current state of the blockchain at the most recent block
  * `earliest` — the earliest available or genesis block.
  * `pending` — the pending state and transactions block. The current state of transactions that have been broadcast to the network but have not yet been included in a block.

<Note>
  See the [default block parameter](https://ethereum.org/en/developers/docs/apis/json-rpc/#default-block).
</Note>

## Response

`data` — the data stored in the storage slot. Returned as a hexadecimal string.

## `eth_getStorageAt` code examples

The following example returns the storage value at slot `0` from the [Chainlink VRFCoordinatorV2](https://polygonscan.com/address/0xAE975071Be8F8eE67addBC1A82488F1C24858067#code) on the Polygon mainnet. In this case, this is the address owning the smart contract.

This method can retrieve the different storage values in time by querying different blocks in the past. Note that to query a state in the past, you need an [archive node](https://chainstack.com/evm-nodes-a-dive-into-the-full-vs-archive-mode).

<Note>
  curl needs a `HEX String` starting with `0x` to identify the block if you want to use a hex integer block number as a parameter.\
  For example, block number `14000000` will be `0xD59F80`.
</Note>

<CodeGroup>
  ```javascript web3.js theme={"system"}
  const Web3 = require("web3");
  const NODE_URL = "CHAINSTACK_NODE_URL";
  const web3 = new Web3(NODE_URL);

  async function getstorage(address, slot, block) {
    const storage = await web3.eth.getStorageAt(address, slot, block)
    console.log(storage)
   }
   
   getstorage("0xAE975071Be8F8eE67addBC1A82488F1C24858067", 0, "latest" )
  ```

  ```javascript ethers.js theme={"system"}
  const ethers = require('ethers');
  const NODE_URL = "CHAINSTACK_NODE_URL";
  const provider = new ethers.JsonRpcProvider(NODE_URL);

  const getstorage = async (address, slot, block) => {
      const storage = await provider.send("eth_getStorageAt", [address, slot, block]);
      console.log(storage);
    };

  getstorage("0xAE975071Be8F8eE67addBC1A82488F1C24858067", "0", "latest" )
  ```

  ```python web3.py theme={"system"}
  from web3 import Web3  
  node_url = "CHAINSTACK_NODE_URL" 

  storage = web3.eth.get_storage_at("0xAE975071Be8F8eE67addBC1A82488F1C24858067", 0, "latest")
  print(web3.to_hex(storage))
  ```
</CodeGroup>

## Use case

One use case for `eth_getStorageAt` is analyzing how the value stored at a specific storage slot of a smart contract changes over time. For example, a developer may want to track the change in a specific variable of a smart contract, such as the total supply of a token, and perform some analysis on it.

Here's an example implementation of this use case using web3.js.

The following program analyzes the [Wrapped Ether](https://polygonscan.com/token/0x7ceb23fd6bc0add59e62ac25578270cff1b9f619#code) smart contract on the Polygon chain to track how the total supply changes over time.

The storage slot matches the position of the variable in the smart contract; the following code snippet shows the top of the WETH smart contract where the variables used in this program are declared.

```sol ERC20.sol theme={"system"}
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;
    using Address for address;
	
  // Variables declared
    mapping (address => uint256) private _balances;	// Storage slot 0x0

    mapping (address => mapping (address => uint256)) private _allowances; // Storage slot 0x1

    uint256 private _totalSupply; // Storage slot 0x2

    string private _name; // Storage slot 0x3
    string private _symbol;	// Storage slot 0x4
    uint8 private _decimals;	// Storage slot 0x5
  .
  .
  .
```

Here's an example implementation of this use case using web3.js:

```javascript index.js theme={"system"}
const Web3 = require("web3");
const NODE_URL = "CHAINSTACK_NODE_URL";
const web3 = new Web3(NODE_URL);

// You need an archive node is going more than 127 blocks in the past.

async function getStorageValueOverTime() {
  // The address of the WETH smart contract
  const wethAddress = '0x7ceB23fD6bC0adD59E62ac25578270cFf1b9f619';

  // The index of the storage slots where the total supply and name data are stored
  const totalSupplySlot = 2;
  const nameSlot = 3;

  // The range of blocks to analyze
  const startBlock = 16000000;
  const endBlock = await web3.eth.getBlockNumber();

  for (let blockNumber = startBlock; blockNumber <= endBlock; blockNumber++) {

    // Retrieve the name and total supply from the smart contract storage at each block
    const [name, supply] = await Promise.all([
      web3.eth.getStorageAt(wethAddress, nameSlot, blockNumber),
      web3.eth.getStorageAt(wethAddress, totalSupplySlot, blockNumber)
    ]);

    // Decode the name and total supply from hexadecimal format to their original values
    const decodedName = web3.utils.hexToUtf8(name);
    const decodedSupply = web3.utils.toBN(supply);

    // Convert the total supply from Wei to Ether and round to 4 decimal places
    const convertedSupply = web3.utils.fromWei(decodedSupply, 'ether');
    const adjustedSupply = Number(convertedSupply).toFixed(4);

    // Output the block number, name, and total supply for each block
    console.log(`Block ${blockNumber}: Name = ${decodedName}, Total supply = ${adjustedSupply}`);
  }
}

async function main() {
  try {
    await getStorageValueOverTime();
  } catch (error) {
    console.error(error);
  }
}

main();
```

The bulk of the program is the `getStorageValueOverTime` function.

The `getStorageValueOverTime` function retrieves and outputs the name and total supply of the WETH smart contract at each block height between a specified start block and the current block height.

The function begins by declaring constants for the WETH contract address, the storage slot indices for the name and total supply data, the starting block height, and the current block height.

Next, the function enters a `for` loop that iterates over every block between the start block and the current block height. Within the loop, the function retrieves the name and total supply from the smart contract storage at the current block height using the `web3.eth.getStorageAt` method.

The `Promise.all` method is used to retrieve the name and total supply in parallel for improved efficiency. The `web3.utils.hexToUtf8` method is then used to convert the name from hexadecimal format to its original string value.

The `web3.utils.toBN` method is used to convert the total supply from hexadecimal format to a `BigNumber object`, which can be used for mathematical operations. The `web3.utils.fromWei` method is then used to convert the total supply from wei to ether.

Finally, the `Number` and `toFixed` methods are used to round the total supply to four decimal places and output the block number, name, and total supply for each block; note that this is for readability, and you should use the raw wei data to make calculations.

Overall, the `getStorageValueOverTime` function provides a way to monitor changes in the state of a smart contract over time, which can be useful for understanding the contract's behavior and performance.


## OpenAPI

````yaml /openapi/polygon_node_api/account_info/eth_getStorageAt.json POST /a9bca2f0f84b54086ceebe590316fff3
openapi: 3.0.0
info:
  title: eth_getStorageAt example
  version: 1.0.0
  description: This is an API example for eth_getStorageAt.
servers:
  - url: https://nd-828-700-214.p2pify.com
security: []
paths:
  /a9bca2f0f84b54086ceebe590316fff3:
    post:
      tags:
        - upload
      summary: eth_getStorageAt
      operationId: getStorageAt
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              properties:
                method:
                  type: string
                  default: eth_getStorageAt
                params:
                  type: array
                  items:
                    anyOf:
                      - type: string
                        default: '0xAE975071Be8F8eE67addBC1A82488F1C24858067'
                      - type: string
                        default: '0x0'
                      - type: string
                        default: latest
                  default:
                    - '0xAE975071Be8F8eE67addBC1A82488F1C24858067'
                    - '0x0'
                    - latest
      responses:
        '200':
          description: The storage information
          content:
            application/json:
              schema:
                type: object
                properties:
                  jsonrpc:
                    type: string
                  id:
                    type: integer
                  result:
                    type: object

````