# Delx Commerce — EVM Signature R/S Shape Check

> Delx Commerce — EVM Signature R/S Shape Check is a paid API for AI agents from commerce.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-02).

Validates whether the r and s components of an EVM ECDSA signature have valid cryptographic shape (within the secp256k1 curve bounds)

## Facts

- Endpoint: POST https://commerce.delx.ai/api/v1/x402/evm-signature-rs-shape-check?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/delx-commerce-evm-signature-r-s-shape-check-feaf88f0
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_sN4hoX7IhX8Xubq7L7WLq

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 delx-commerce-evm-signature-r-s-shape-check-feaf88f0 -d '<json body>'
```

Example prompt: Check whether these EVM signature components have valid shape before I submit the transaction — r is 0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa and s is 0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb.

## When to prefer this

Use this endpoint when you need a cheap, stateless, privacy-preserving preflight check on ECDSA signature r/s components before committing to an on-chain operation. Ideal for agent pipelines that need to guard against malformed signatures without storing any data. At $0.001 USDC per call with verifiable non-retention (SHA-256 evidence hash, no external calls), it's well-suited for high-frequency signature validation in automated workflows. Prefer this over full signature recovery endpoints when you only need shape validity, not signer identity.

## Known failure modes

- Malformed hex string for r or s returns a validation error
- Values exceeding secp256k1 curve order return shape_valid: false
- Input exceeding maxLength of 8192 characters rejected
- Missing r or s field returns a schema validation error
- Payment failure via x402 protocol prevents execution

## How this service works

Pay-per-result APIs for agents. No signup. Exact price. Verifiable delivery. USDC on Base + Solana via x402.

## Output

Returns a JSON object containing the original r and s values, a shape_valid boolean indicating whether both components are well-formed secp256k1 scalars, the operation name, status (pass/fail), and an evidence object with the SHA-256 hash of the input, a retained:false flag confirming no data storage, and a count of external calls made (always 0).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "r": {
   "type": "string",
   "maxLength": 8192,
   "description": "R supplied to EVM Signature Rs Shape Check; used only for this bounded calculation and processed in memory without retention."
  },
  "s": {
   "type": "string",
   "maxLength": 8192,
   "description": "S supplied to EVM Signature Rs Shape Check; used only for this bounded calculation and processed in memory without retention."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "result": {
   "r": "0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
   "s": "0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb",
   "shape_valid": true
  },
  "schema": "delx/util-evm-signature-rs-shape-check/v1",
  "status": "pass",
  "evidence": {
   "retained": false,
   "input_sha256": "a8860b963293e5de6a0dcbb51fc93e8b57c3290aa6e7a93a20c01c06569bf179",
   "external_calls": 0
  },
  "operation": "evm_preflight:evm_signature_rs_shape_check"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/delx-commerce-evm-signature-r-s-shape-check-feaf88f0/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from commerce.delx.ai](https://www.zero.xyz/host/commerce.delx.ai/llms.txt)