# SignalHarness EVM Storage Slot Compute

> SignalHarness EVM Storage Slot Compute is a paid API for AI agents from signalharness.ai, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-16).

Computes the EVM storage slot for a given smart contract storage variable based on caller-supplied input data.

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/evm_storage_slot_compute/invoke
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signalharness-evm-storage-slot-compute-695a1c5f
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Uz90o32XWjzU1VZkS7UC9

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 signalharness-evm-storage-slot-compute-695a1c5f -d '<json body>'
```

Example prompt: Can you compute the EVM storage slot for the 'balances' mapping in a Solidity contract where the key is address 0xABC123... and balances is at slot 0? I need the exact storage slot value.

## When to prefer this

Choose this endpoint when you need programmatic, on-demand EVM storage slot derivation without setting up a local Solidity compiler or ABI decoder. It is particularly useful for agents that need to call eth_getStorageAt dynamically, audit contract storage layouts, or verify proxy implementation slots — especially when the agent cannot run code locally. At $0.01 USDC per call via x402, it is cost-effective for one-off lookups within an agentic workflow on Base.

## Known failure modes

- Malformed or ambiguous storage_slot_request string returns an error or warning-laden result
- Unsupported storage layout patterns may produce incorrect slots without error
- Input exceeding 65536 characters is rejected
- Missing required fields in the request body returns a 400-level error
- Payment failure via x402 protocol results in 402 response before execution

## How this service works

Explore 330 pay-per-call x402 API services and 27 agent-native digital products, with Base USDC pricing, secure Polar checkout, and free discovery.

## Output

Returns a JSON object containing the computed EVM storage slot as a hex string, any relevant warnings about the input (e.g. ambiguous layout), the service ID, and an evidence scope field indicating the data was caller-supplied. Also includes a full receipt with payment ID, network (Base/eip155:8453), latency, and a SHA-256 hash of the result for auditability.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "storage_slot_request": {
   "type": "string",
   "maxLength": 65536,
   "minLength": 2
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "replay": false,
  "result": {
   "warnings": [
    "The caller must supply the correct layout and key encoding."
   ],
   "service_id": "evm_storage_slot_compute",
   "evidence_scope": "caller_supplied_data",
   "computed_storage_slot": "{\"key_type\":\"address\",\"kind\":\"mapping\",\"slot\":\"0xada5013122d395ba3c54772283fb069b10426056ef8ca54750cb9bb552a59e7d\"}"
  },
  "status": "succeeded",
  "receipt": {
   "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
   "usage": [],
   "status": "succeeded",
   "network": "eip155:8453",
   "artifacts": [],
   "endedAtMs": 0,
   "latencyMs": 0,
   "paymentId": "example-payment",
   "receiptId": "example-receipt",
   "requestId": "example-request",
   "serviceId": "evm_storage_slot_compute",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "10000",
   "resultSha256": "94541795270ec7665897e175fb93dc62b62434198e94b61c30e6dd324d327b5c",
   "serviceVersion": "1.0.0",
   "settlementReference": "0x0000000000000000000000000000000000000000000000000000000000000000"
  },
  "artifacts": [],
  "requestId": "example-request",
  "executionId": "example-execution"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/signalharness-evm-storage-slot-compute-695a1c5f/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from signalharness.ai](https://www.zero.xyz/host/signalharness.ai/llms.txt)