trace_call

trace_call runs a transaction through the EVM against the state of a chosen Ethereum block, then hands you the trace without ever broadcasting anything or spending a wei of ETH. Nothing is mined, no nonce moves. You describe the call you're curious about, pick which views you want back, and the node replays it as if it had executed at that block. On Ethereum mainnet (chain ID 1) this is the OpenEthereum/Parity-flavour simulation: it can return a flat call-tree trace, an opcode-level vmTrace, and a stateDiff showing which account balances, nonces, contract code, and storage entries the call would rewrite. Send the request to https://ethereum.therpc.io/YOUR_API_KEY and supply at least one trace type alongside your call object.

Use cases

See every internal call a transaction would fan out into before you sign it. Request ["trace"] and inspect the nested CALLs to confirm a Uniswap swap routes the way you expect.
Validate expected writes by diffing storage. Ask for ["stateDiff"] and check that a prospective transaction only modifies the slots it should, catching an approval or balance bug before it reaches the mempool.
Replay contract logic against a past block. Pass a historical block number to test how a call behaves under the state that existed then. That history lookup needs a trace-enabled archive node.

Parameters

#	Name	Type	Required	Description
1	`transaction`	object	Yes	Call object: `from?`, `to`, `gas?`, `gasPrice?`, `value?`, `data?`.
2	`traceTypes`	array	Yes	Array of trace types to include: `"trace"` (call tree), `"vmTrace"` (opcode-level), `"stateDiff"` (storage/balance diffs).
3	`blockParameter`	string	No	Block state against which to simulate the call.Default: `latest`

Response

Type	Description
object	`{output, trace?, stateDiff?, vmTrace?}` — `trace` is a flat call-tree array, `stateDiff` maps each touched address to its balance/nonce/code/storage diffs, `vmTrace` provides opcode-level detail (Parity-format).

Example request

1curl https://ethereum.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H "Content-Type: application/json" \
4  -d '{
5    "jsonrpc": "2.0",
6    "method": "trace_call",
7    "params": [
8        {
9          "to": "0x0000000000000000000000000000000000000000",
10          "data": "0x"
11        },
12        [
13          "trace"
14        ],
15        "latest"
16      ],
17    "id": 1
18  }'

Try it live in the Ethereum playground.

Errors & troubleshooting

Code	Message	Cause
`-32601`	`Method not found`	trace namespace not enabled or client does not support trace_call.
`-32602`	`Invalid params`	Transaction object missing required fields, traceTypes array is empty or contains unrecognized values, or blockParameter is invalid.
`-32000`	`execution reverted`	Simulated call reverted; partial trace is still returned.

Common pitfalls

Asking for all three types at once (trace, vmTrace, stateDiff) inflates the response fast, especially for a call into a deep DeFi protocol. Request only the views you'll actually read.
Simulating against any block other than the recent head pulls historical state, which is only available from an archive node with the trace API enabled.
The vmTrace is the Parity opcode format, not Geth's structLog. If you've been parsing debug_traceCall output, the field layout here is different and your parser won't carry over unchanged.

Supported networks

Mainnet — Chain ID: 1
Sepolia — Chain ID: 11155111