debug_traceBlock

debug_traceBlock takes a block you supply as RLP-encoded bytes, re-executes it against its parent state on an Arbitrum One node, and returns an opcode-level trace for every transaction in block order. Unlike the by-hash and by-number variants, here you hand the node the block payload itself rather than a reference. Arbitrum One is a Nitro Optimistic Rollup (chain ID 42161) that prices gas in ETH, so the node replays the ArbOS execution exactly as the sequencer would have. Point requests at https://arbitrum.therpc.io/YOUR_API_KEY and pass an optional tracer config to control the output shape.

Use cases

• Trace a custom or modified block that is not yet on Arbitrum One — for example one built in a local Nitro simulation environment — to see how it would execute.
• Reproduce a block's execution when you already hold its RLP bytes, such as from a feed-relay or p2p capture, without first having to register it by hash.

Parameters

Response

Example request

1curl https://arbitrum.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H "Content-Type: application/json" \
4  -d '{
5    "jsonrpc": "2.0",
6    "method": "debug_traceBlock",
7    "params": [
8        "0xf9...",
9        {}
10      ],
11    "id": 1
12  }'

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• Producing valid RLP for an Arbitrum One block is fiddly — most callers fetch the block via eth_getBlockByHash with full transactions, then re-encode it, and a malformed payload returns -32602.
• The parent state of a historical block must be present, so tracing old blocks needs an archive node with the matching ArbOS state.
• Performance matches debug_traceBlockByHash: this is a full block replay, so dense blocks are heavy and may need a compact tracer.

Supported networks

• Mainnet — Chain ID: 42161
• Sepolia — Chain ID: 421614

See also

• debug_traceBlockByNumber
• debug_traceBlockByHash
• debug_traceTransaction

1curl https://arbitrum.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H 'Content-Type: application/json' \
4  -d '{"jsonrpc":"2.0","id":1,"method":"debug_traceBlock","params":["",{}]}'