debug_traceBlockByHash | BNB Chain

BNB API method that traces the execution of a block. This method can be used to debug and analyze smart contracts and transactions on the BNB blockchain. It provides a detailed trace of the execution of a block, including information on all the transactions and calls that interacted with the block, as well as the gas used, memory, storage operations, and other performance metrics for each operation.


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  • hash β€” the hash of the block to be traced.
  • tracer β€” an object identifying the type of tracer and its configuration:
    • 4byteTracer β€” tracer that captures the function signatures and call data sizes for all functions executed during a transaction, creating a map that links each selector and size combination to the number of times it occurred. This provides valuable information about the frequency and usage of each function within the transaction.
    • callTracer β€” tracer that captures information on all call frames executed during a transaction. The resulting nested list of call frames is organized into a tree structure that reflects the way the Ethereum Virtual Machine works and can be used for debugging and analysis purposes.
    • prestateTracer β€” tracer with two modes: prestate and diff, where the former returns the accounts needed to execute a transaction, and the latter returns the differences between the pre and post-states of the transaction. The tracer operates by re-executing the transaction and tracking every state change made, resulting in an object with the account addresses as keys and the corresponding trie leaves as values.

Response types

4byteTracer response

  • object β€” the 4byteTracer traces object:
    • result β€” a map of the function signature, the call data size, and how many times the function was called.

callTracer response

  • object β€” the callTracer traces object:
    • from β€” the address of the sender who initiated the transaction.
    • gas β€” the units of gas included in the transaction by the sender.
    • gasused β€” the total used gas by the call. Encoded as hexadecimal.
    • to β€” the address of the recipient of the transaction if it was a transaction to an address. For contract creation transactions, this field is null.
    • input β€” the optional input data sent with the transaction, usually used to interact with smart contracts.
    • output β€” the return value of the call, encoded as a hexadecimal string.
    • error β€” an error message in case the execution failed.
    • revertReason β€” the reason why the transaction was reverted, returned by the smart contract if any.
    • calls β€” a list of sub-calls made by the contract during the call, each represented as a nested call frame object.

prestateTracer response

  • object β€” the prestateTracer traces object:
    • smart contract address β€” the address of the smart contract associated with the result.
      • balance β€” the balance of the contract, expressed in wei and encoded as a hexadecimal string.
      • code β€” the bytecode of the contract, encoded as a hexadecimal string.
      • nonce β€” the nonce of the account associated with the contract, represented as an unsigned integer.
      • storage β€” a map of key-value pairs representing the storage slots of the contract. The keys and values are both encoded as hexadecimal strings.

debug_traceBlockByHash code examples

const { Web3, Web3PluginBase } = require('web3');
const web3 = new Web3(NODE_URL);

// Define the TraceBlockPlugin class
class TraceBlockPlugin extends Web3PluginBase {
    pluginNamespace = 'trace';

    async traceBlockByHash(blockHash, tracer) {
        return this.requestManager.send({
            method: 'debug_traceBlockByHash',
            params: [blockHash, tracer],

// Register the plugin
web3.registerPlugin(new TraceBlockPlugin());

// Function to trace block by hash using the custom plugin
async function traceBlockByHash(blockHash) {
    const tracer = { tracer: '4byteTracer' }; // Or any other tracer you want to use
    try {
        const result = await web3.trace.traceBlockByHash(blockHash, tracer);
    } catch (error) {
        console.error("Error tracing block by hash:", error);

// Call the function with a specific block hash
const ethers = require('ethers');
const provider = new ethers.JsonRpcProvider(NODE_URL);

const traceBlockByHash = async (blockHash) => {

  // Specify the type of tracer: 4byteTracer, callTracer, or prestateTracer
  const tracer = { tracer: '4byteTracer' };
  const traces = await provider.send("debug_traceBlockByHash", [blockHash, tracer]);

from web3 import Web3  
web3 = Web3.HTTPProvider(node_url)

block_hash = "0x0e77e2cf5a6999f616b56f1378b6c7b127b5a4e20cb2e12611d808af0979dacf"

# Specify the type of tracer: 4byteTracer, callTracer, or prestateTracer
tracer = { "tracer": '4byteTracer' }
block_traces = web3.provider.make_request('debug_traceBlockByHash', [block_hash, tracer])

Use case

One practical use case for debug_traceBlockByHash with the 4byteTracer tracer would be for auditing or analysis purposes of a blockchain.

For example, if there are token contracts on the blockchain and the transfer function of these contracts is used to send tokens between users, a developer could use the debug_traceBlockByHash method with the 4byteTracer tracer to trace the transactions in a given block and count how many times the transfer function was called.

Try the debug_traceBlockByHash RPC method yourself

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