# TxSim Decoder API — EVM Simulation & Calldata Decoder

> TxSim Decoder API — EVM Simulation & Calldata Decoder is a paid API for AI agents from simulate.cyberwarex.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-02).

Decodes raw EVM calldata into a named function with security risk flags and runs a keyless eth_call preview to determine if a transaction would succeed or revert before signing.

## Facts

- Endpoint: GET https://simulate.cyberwarex.com/simulate?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/txsim-decoder-api-evm-simulation-calldata-decoder-dc27eab0
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_hE4hduMZSG1et6HX8uISg

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 txsim-decoder-api-evm-simulation-calldata-decoder-dc27eab0
```

Example prompt: Before I sign this transaction, can you decode the calldata 0xa9059cbb000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa960450000000000000000000000000000000000000000000000000000000005f5e100 targeting contract 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 on Base, tell me what function it calls, flag any security risks, and simulate whether it would succeed?

## When to prefer this

Choose this endpoint when you need a keyless, infrastructure-free way to decode raw EVM calldata and/or simulate a transaction across Base, Ethereum, Arbitrum, Optimism, Polygon, or BSC before signing. Ideal for agents performing pre-sign safety checks without managing RPC nodes or API keys. Prefer this over full tracing RPCs for lightweight decode+simulate needs; use a tracing RPC for full asset-change tracking (v2 feature).

## Known failure modes

- Invalid or malformed 'to' address returns a validation error
- Unsupported chain name returns an enum validation error
- Malformed or unrecognized calldata hex may result in an undecoded response with null decoded fields
- Network or RPC issues for the target chain may cause simulation failures
- Transactions that depend on real-time state (e.g. slippage-sensitive swaps) may show would_succeed=true but revert at broadcast time
- Missing 'to' parameter (required) returns a schema validation error

## How this service works

Pay-per-call EVM transaction simulation and calldata decoder for agents: decode raw calldata into a named function with security risk flags, and run a keyless eth_call preview to see whether a transaction would succeed or revert before signing. Across base, ethereum, arbitrum, optimism, polygon, bsc. Deterministic JSON, no RPC keys or node infra needed.

## Output

A JSON object containing: the decoded function name, signature, and named arguments; a risk assessment with a level (none, caution, or danger) and specific flags; a would_succeed boolean indicating if the eth_call simulation passed; a revert_reason string if it failed; asset_changes (v2, requires tracing RPC); and contextual notes and disclaimers about simulation limitations.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "to"
     ],
     "properties": {
      "to": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{40}$",
       "description": "Target contract or account address."
      },
      "data": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]*$",
       "description": "Transaction calldata (hex)."
      },
      "from": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{40}$",
       "description": "Sender address for the eth_call preview."
      },
      "chain": {
       "enum": [
        "base",
        "ethereum",
        "arbitrum",
        "optimism",
        "polygon",
        "bsc"
       ],
       "type": "string",
       "default": "base",
       "description": "EVM chain to simulate on."
      },
      "value": {
       "type": "string",
       "description": "Native value in wei (optional, decimal or 0x hex)."
      }
     },
     "additionalProperties": false
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "to": {
       "type": "string"
      },
      "note": {
       "type": "string"
      },
      "risk": {
       "type": "object",
       "description": "level (none|caution|danger) + flags."
      },
      "chain": {
       "type": "string"
      },
      "decoded": {
       "type": "object",
       "description": "function, signature, args."
      },
      "disclaimer": {
       "type": "string"
      },
      "asset_changes": {
       "type": "null",
       "description": "v2: needs a tracing RPC key."
      },
      "revert_reason": {
       "type": [
        "string",
        "null"
       ]
      },
      "would_succeed": {
       "type": [
        "boolean",
        "null"
       ]
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "note": "asset-level change tracing requires a tracing RPC key (v2)",
  "risk": {
   "flags": [],
   "level": "none"
  },
  "chain": "base",
  "decoded": {
   "args": {
    "to": "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045",
    "amount": "100000000"
   },
   "function": "transfer",
   "signature": "transfer(address,uint256)"
  },
  "disclaimer": "Static decode + keyless eth_call preview only. This is not financial advice and not a guarantee: a call that would succeed now can still revert at broadcast time (state changes, slippage, MEV). Always verify before signing.",
  "asset_changes": null,
  "revert_reason": null,
  "would_succeed": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/txsim-decoder-api-evm-simulation-calldata-decoder-dc27eab0/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from simulate.cyberwarex.com](https://www.zero.xyz/host/simulate.cyberwarex.com/llms.txt)