# EVM Signature R/S Shape Check

> EVM Signature R/S Shape Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Validates that EVM ECDSA signature components R and S are correctly shaped (well-formed hex values of expected length/format) without any external calls or data retention.

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/evm-signature-rs-shape-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/evm-signature-r-s-shape-check-2c1574b0
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_h_ZCLUGakYVYwSVIyMXmr

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 evm-signature-r-s-shape-check-2c1574b0 -d '<json body>'
```

Example prompt: Before I submit this Ethereum transaction, can you check whether these signature components are correctly shaped — r is 0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa and s is 0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb?

## When to prefer this

Choose this endpoint when you need a fast, stateless, auditable preflight check that EVM ECDSA signature R and S components are correctly shaped before using them in a transaction, smart contract call, or further cryptographic operation. It is ideal in agentic pipelines where you want a zero-retention, zero-external-call validation step with a verifiable input hash for audit trails. Prefer this over manual regex checks or full signature verification libraries when you only need shape validation (not full cryptographic signature recovery or verification against a message hash).

## Known failure modes

- Malformed or missing r/s fields return a shape_valid: false result rather than an error
- Inputs exceeding 8192 characters may be rejected with a payload error
- Invalid JSON request body returns a 400-level HTTP error
- Network or service unavailability returns a 5xx error
- Non-hex or incorrectly prefixed values will likely yield shape_valid: false

## How this service works

EVM Signature Rs Shape Check: EVM Signature Rs Shape Check checks r and s values as 32-byte hexadecimal scalars from bounded caller-supplied values without an external provider. Call EVM Signature Rs Shape Check before signing, submitting, replacing, or accepting an EVM/Base transaction assembled from caller-owned data. Returns normalized transaction evidence, calculated budget or shape findings, and a fail-closed preflight status for EVM Signature Rs Shape Check as versioned deterministic JSON…

## Output

Returns a JSON object containing the echoed R and S values, a boolean `shape_valid` field indicating whether both components are well-formed EVM signature values, the operation name, a pass/fail status, and an evidence block confirming no data was retained and no external calls were made (including an input SHA-256 hash for auditability).

## 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/evm-signature-r-s-shape-check-2c1574b0/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.delx.ai](https://www.zero.xyz/host/api.delx.ai/llms.txt)