# OneSource Ethereum Storage Slot Reader

> OneSource Ethereum Storage Slot Reader is a paid API for AI agents from api.onesource.io, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-16).

Reads a raw storage slot value from an Ethereum smart contract at a specified block on mainnet or Sepolia testnet

## Facts

- Endpoint: GET https://api.onesource.io/api/chain/storage
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/onesource-ethereum-storage-slot-reader-45fc26b3
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_fsjK3BlcodS3AFCZj_51V

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability onesource-ethereum-storage-slot-reader-45fc26b3
```

Example prompt: What's the value stored in storage slot 0x0 of the USDT contract (0xdac17f958d2ee523a2206206994597c13d831ec7) on Ethereum mainnet at the latest block?

## When to prefer this

Use this endpoint when you need low-level EVM storage slot access — for inspecting raw contract state, reading packed storage variables, or verifying on-chain data that isn't exposed through a contract's public ABI. Prefer this over higher-level contract call endpoints when you know the specific storage layout or need bytes32 values directly. Ideal for agents auditing contracts, verifying token balances at a storage level, or reading proxy implementation slots.

## Known failure modes

- Invalid contract address format returns 4xx validation error
- Invalid slot hex string returns 4xx validation error
- Contract does not exist at that block returns zero value
- Invalid block number or tag returns error
- Network not 'ethereum' or 'sepolia' returns validation error
- Payment failure via x402/MPP returns 402 Payment Required

## How this service works

Read a raw storage slot from any Ethereum contract via eth_getStorageAt

## Output

Returns a JSON object containing the queried contract address, the storage slot index, the block reference, and the 32-byte hex-encoded value stored at that slot (e.g. '0x0000000000000000000000000000000000000000000000000000000000000001')

## Example request

```json
{
 "slot": "0x1",
 "block": "latest",
 "network": "ethereum",
 "contract": "0x1f9840a85d5af5bf1d1762f925bdaddc4201f984"
}
```

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "contract",
      "slot"
     ],
     "properties": {
      "slot": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]+$"
      },
      "block": {
       "oneOf": [
        {
         "type": "integer",
         "minimum": 0
        },
        {
         "enum": [
          "latest",
          "pending",
          "earliest",
          "safe",
          "finalized"
         ],
         "type": "string"
        },
        {
         "type": "string",
         "pattern": "^0[xX][a-fA-F0-9]+$"
        }
       ]
      },
      "network": {
       "enum": [
        "ethereum",
        "sepolia",
        "robinhood"
       ],
       "type": "string",
       "default": "ethereum"
      },
      "contract": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{40}$"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "data",
      "meta"
     ],
     "properties": {
      "data": {
       "type": "object",
       "properties": {
        "value": {
         "type": "string"
        }
       },
       "description": "Endpoint-specific response payload"
      },
      "meta": {
       "type": "object",
       "required": [
        "endpoint",
        "request_id"
       ],
       "properties": {
        "endpoint": {
         "type": "string"
        },
        "cost_usdc": {
         "type": "string"
        },
        "request_id": {
         "type": "string"
        },
        "payment_chain": {
         "type": "string"
        },
        "payment_token": {
         "type": "string"
        }
       }
      },
      "error": {
       "type": [
        "object",
        "null"
       ],
       "properties": {
        "code": {
         "type": "integer"
        },
        "message": {
         "type": "string"
        }
       }
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "data": {
   "value": "0x0000000000000000000000000000000000000000000000000000000000000001"
  },
  "meta": {
   "endpoint": "/api/chain/storage",
   "cost_usdc": "0.001",
   "request_id": "00000000abcdef01",
   "payment_chain": "base",
   "payment_token": "USDC"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/onesource-ethereum-storage-slot-reader-45fc26b3/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.onesource.io](https://www.zero.xyz/host/api.onesource.io/llms.txt)