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SignalHarness EVM Storage Slot Compute
x402
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.
Price / call$0.01
Success—
StatusUnknown
How this service works
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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.
Example use cases
Read raw balance from contract storage
“I need to call eth_getStorageAt on an ERC-20 contract to read a specific user's balance directly — can you compute the storage slot for the 'balances' mapping at base slot 1 with key address 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045?”
Verify upgradeable proxy implementation slot
“What is the EVM storage slot for the implementation address in an OpenZeppelin TransparentUpgradeableProxy? I want to double-check the slot before calling eth_getStorageAt on mainnet.”
Debug Solidity storage layout collision
“I think two variables in my Solidity contract are colliding in storage — can you compute the slots for a uint256 at position 2 and the first element of a dynamic array also declared around slot 2 so I can compare them?”
Technical details
Endpoint
POSThttps://signalharness.ai/api/agent/services/evm_storage_slot_compute/invokeWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| storage_slot_request | string |
Output
Schema · Response
{
"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"
}
}Tags
x402
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