# SignalHarness EOA Signature Verifier

> SignalHarness EOA Signature Verifier 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).

Verifies an Ethereum EOA (Externally Owned Account) cryptographic signature against caller-supplied data and returns the verification result with warnings and evidence scope.

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/eoa_signature_verify/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-eoa-signature-verifier-51d2aac8
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_zPE5tLOuKYI9qUgxvajTL

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-eoa-signature-verifier-51d2aac8 -d '<json body>'
```

Example prompt: Can you verify this Ethereum EOA signature for me? Here's the signature request payload — I need to know if it's valid, who signed it, and whether it's a replay.

## When to prefer this

Use this endpoint when you need a pay-per-call, agent-native EOA signature verification service that integrates with the x402 micropayment protocol on Base (EIP-155:8453). Ideal for AI agents operating autonomously in Web3 contexts where per-call billing via USDC is preferred over subscription APIs, and where replay detection and evidence scoping are needed alongside basic signature validation.

## Known failure modes

- Malformed or truncated signature string returns validation error
- Signature string exceeds 65536 character limit
- Replay attack detected and flagged in warnings
- Invalid Ethereum address format in payload
- Signature does not match the claimed signer
- Network or service unavailability returns non-200 status
- Payment failure via x402 protocol blocks 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: a boolean 'replay' flag indicating whether the signature appears to be a replay, an 'eoa_signature_verification' result string with the verification outcome, a list of 'warnings', an 'evidence_scope' string (e.g. 'caller_supplied_data'), a status field ('succeeded'), and a full receipt with payment metadata including network, asset, payment ID, request ID, execution ID, timestamps, and a SHA-256 hash of the result.

## Request schema (JSON Schema)

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

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "replay": false,
  "result": {
   "warnings": [
    "Verification proves key control for the supplied message only, not identity or authorization."
   ],
   "service_id": "eoa_signature_verify",
   "evidence_scope": "caller_supplied_data",
   "eoa_signature_verification": "{\"address\":\"0x0000000000000000000000000000000000000001\",\"encoding\":\"utf8\",\"valid\":false}"
  },
  "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": "eoa_signature_verify",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "10000",
   "resultSha256": "5fb43bede3ca02db81d5e0fc5a48a9e770301df3402aca41ef7f62d1e73cf6c8",
   "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-eoa-signature-verifier-51d2aac8/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)