Debug Tracing Overview

Comprehensive guide to debugging and tracing EVM transactions on Sei. Learn to analyze transaction execution, optimize gas usage, and troubleshoot smart contracts with real examples and end-to-end workflows.

Requirements

The examples in this guide call the debug JSON-RPC endpoints directly with curl — no SDK or additional libraries are required. Optionally install jq to pretty-print the JSON responses:

# macOS
brew install jq

# Debian/Ubuntu
sudo apt-get install jq

Debug tracing is your primary tool for understanding EVM transaction execution on Sei. This comprehensive system allows you to analyze transaction flow, optimize gas usage, debug smart contract interactions, and troubleshoot production issues.

What You Can Trace

Transaction Execution

• Step-by-step opcode execution
• Contract call hierarchy
• Gas consumption breakdown
• State changes and storage access

Contract Interactions

• Cross-contract calls and returns
• Event emission analysis
• Precompile usage tracking
• External library calls

Performance Analysis

• Gas optimization opportunities
• Bottleneck identification
• Cache hit/miss patterns
• State access efficiency

Security Analysis

• Suspicious operation detection
• Reentrancy pattern analysis
• Access control verification
• Vulnerability scanning

Available Tracing Methods

Method	Purpose	Use Case
debug_traceTransaction	Trace specific transaction	Debugging failed transactions
debug_traceBlockByNumber	Trace entire block	Block-level analysis

When debug_traceBlockByNumber or debug_traceBlockByHash run with the default (struct) tracer — that is, when no custom tracer is specified — Sei can use a parallelized block trace path in which a failed transaction no longer aborts the entire block trace. Instead, each transaction produces its own per-tx entry in the result array: successful transactions include a result field, while failed transactions include an error field. This lets you inspect every transaction in a block even when one or more of them fail.

This parallelized path is opt-in and gated by the node config field evm.enable_parallelized_block_trace (default false). When it is disabled, or when an explicit tracer is specified, the legacy trace path is used. Node operators can enable it by setting enable_parallelized_block_trace = true in the [evm] section of app.toml (or via the --evm.enable_parallelized_block_trace flag).

| debug_traceCall | Simulate and trace | Testing before execution | | debug_traceStateAccess | State access patterns | Performance optimization |

Transaction Analysis Example

Tracing an ERC-20 transfer transaction:

Transaction Details

# Real transaction on Sei mainnet
TRANSACTION_HASH="0x75b7ba10248e90db85b224eae587db1728520b6f72c795b9185064f444cee7c3"

# Transaction details

curl -X POST -H "Content-Type: application/json" \
 --data '{
"jsonrpc": "2.0",
"method": "eth_getTransactionByHash",
"params": ["'$TRANSACTION_HASH'"],
"id": 1
}' \
 https://evm-rpc.sei-apis.com

Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "blockHash": "0xbc229fe41605ba2b46fcd7aa7ce328dc2f6da78385dfea84ca8dbef7b4325462",
    "blockNumber": "0x97aefcf",
    "from": "0x4cbee7ad42d33e9d3b41e8b6faca2f6f173c8a94",
    "gas": "0x66f24",
    "gasPrice": "0x565dd756",
    "maxFeePerGas": "0x565dd756",
    "maxPriorityFeePerGas": "0x5e679d6",
    "hash": "0x75b7ba10248e90db85b224eae587db1728520b6f72c795b9185064f444cee7c3",
    "input": "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",
    "nonce": "0x4",
    "to": "0x1231deb6f5749ef6ce6943a275a1d3e7486f4eae",
    "transactionIndex": "0x14",
    "value": "0x0",
    "type": "0x2",
    "accessList": [],
    "chainId": "0x531",
    "v": "0x0",
    "r": "0x3a107aca9cd554a9171a65ea2e8ef56ebeca8cfdc17f4bbecfb0f86837ca90d6",
    "s": "0x426134cf65b701bc8d43162f78bcf787319ff17cc6293188bcbb30fd99feb60",
    "yParity": "0x0"
  }
}

Basic Trace

# Trace the transaction execution
curl -X POST -H "Content-Type: application/json" \
  --data '{
    "jsonrpc": "2.0",
    "method": "debug_traceTransaction",
    "params": [
      "'$TRANSACTION_HASH'",
      {
        "tracer": "callTracer",
        "tracerConfig": {
          "withLog": true
        }
      }
    ],
    "id": 1
  }' \
  https://evm-rpc.sei-apis.com

Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "from": "0x4cbee7ad42d33e9d3b41e8b6faca2f6f173c8a94",
    "gas": "0x66f24",
    "gasUsed": "0x40f98",
    "to": "0x1231deb6f5749ef6ce6943a275a1d3e7486f4eae",
    "input": "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",
    "calls": [
      {
        "from": "0x1231deb6f5749ef6ce6943a275a1d3e7486f4eae",
        "gas": "0x5d03f",
        "gasUsed": "0x3b0cc",
        "to": "0x31a9b1835864706af10103b31ea2b79bdb995f5f",
        "input": "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",
        "calls": [
          {
            "from": "0x1231deb6f5749ef6ce6943a275a1d3e7486f4eae",
            "gas": "0x5aa48",
            "gasUsed": "0xa724",
            "to": "0x3894085ef7ff0f0aedf52e2a2704928d1ec074f1",
            "input": "0x23b872dd0000000000000000000000004cbee7ad42d33e9d3b41e8b6faca2f6f173c8a940000000000000000000000001231deb6f5749ef6ce6943a275a1d3e7486f4eae000000000000000000000000000000000000000000000000000000000004faaa",
            "output": "0x0000000000000000000000000000000000000000000000000000000000000001",
            "calls": [
              {
                "from": "0x3894085ef7ff0f0aedf52e2a2704928d1ec074f1",
                "gas": "0x54283",
                "gasUsed": "0x4ad6",
                "to": "0x0000000000000000000000000000000000001001",
                "input": "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",
                "output": "0x0000000000000000000000000000000000000000000000000000000000000001",
                "value": "0x0",
                "type": "CALL"
              }
            ],
            "logs": [
              {
                "address": "0x3894085ef7ff0f0aedf52e2a2704928d1ec074f1",
                "topics": [
                  "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
                  "0x0000000000000000000000004cbee7ad42d33e9d3b41e8b6faca2f6f173c8a94",
                  "0x0000000000000000000000001231deb6f5749ef6ce6943a275a1d3e7486f4eae"
                ],
                "data": "0x000000000000000000000000000000000000000000000000000000000004faaa",
                "position": "0x1"
              }
            ],
            "value": "0x0",
            "type": "CALL"
          },
          ...
        ]
      }
    ]
  }
}

Gas Analysis

# Analyze gas usage patterns
curl -X POST -H "Content-Type: application/json" \
  --data '{
    "jsonrpc": "2.0",
    "method": "debug_traceTransaction",
    "params": [
      "0x75b7ba10248e90db85b224eae587db1728520b6f72c795b9185064f444cee7c3",
      {
        "tracer": "{gasUsed: 0, operations: {}, step: function(log, db) { var op = log.op.toString(); var cost = log.getCost(); this.gasUsed += cost; if (!this.operations[op]) { this.operations[op] = { count: 0, totalGas: 0 }; } this.operations[op].count++; this.operations[op].totalGas += cost; }, fault: function(log, db) {}, result: function(ctx, db) { return { totalGas: this.gasUsed, operations: this.operations, efficiency: this.gasUsed / ctx.gasUsed }; }}"
      }
    ],
    "id": 1
  }' \
  https://evm-rpc.sei-apis.com

Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "totalGas": 6346011,
    "operations": {
      "PUSH1": {
        "count": 1476,
        "totalGas": 4428
      },
      "MSTORE": {
        "count": 342,
        "totalGas": 1690
      },
      "CALLDATASIZE": {
        "count": 41,
        "totalGas": 82
      },
      "PUSH2": {
        "count": 1400,
        "totalGas": 4200
      },

      ...


      "STOP": {
        "count": 5,
        "totalGas": 0
      },
      "LOG2": {
        "count": 2,
        "totalGas": 5578
      },
      "LOG4": {
        "count": 1,
        "totalGas": 2899
      },
      "LOG1": {
        "count": 1,
        "totalGas": 2542
      }
    },
    "efficiency": 23.84499278564343
  }
}

Debugging Failed Transactions

Steps to analyze and resolve transaction failures:

Step 1: Identify the Problem

# Get transaction receipt
FAILED_TX="0xb2a6f4f7f37d8df728968126c05d1a8b0391003cf375ed5abb1b5e02fe66c717"

curl -X POST -H "Content-Type: application/json" \
  --data '{
    "jsonrpc": "2.0",
    "method": "eth_getTransactionReceipt",
    "params": ["'$FAILED_TX'"],
    "id": 1
  }' \
  https://evm-rpc.sei-apis.com

Step 2: Trace the Execution

# Trace to see where it failed
curl -X POST -H "Content-Type: application/json" \
  --data '{
    "jsonrpc": "2.0",
    "method": "debug_traceTransaction",
    "params": [
      "'$FAILED_TX'",
      {
        "tracer": "callTracer",
        "tracerConfig": {
          "withLog": true
        }
      }
    ],
    "id": 1
  }' \
  https://evm-rpc.sei-apis.com

Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "from": "0x2c80b1b0473bb765ef536d2526ec63195794d945",
    "gas": "0xc3500",
    "gasUsed": "0x2863d",
    "to": "0xd1efe48b71acd98db16fcb9e7152b086647ef544",
    "input": "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",
    "output": "0x08c379a000000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000013546f6f206c6974746c6520726563656976656400000000000000000000000000",
    "error": "execution reverted",
    "revertReason": "Too little received",
    "calls": [
      ...
    ]
  }
}

Step 3: Fix and Test

# Simulate the fix with debug_traceCall
curl -X POST \
  -H "Content-Type: application/json" \
  --data '{
    "jsonrpc": "2.0",
    "method": "debug_traceCall",
    "params": [
      {
        "from": "0x2c80b1b0473bb765ef536d2526ec63195794d945",
        "to": "0xd1efe48b71acd98db16fcb9e7152b086647ef544",
        "gas": "0xc3500",
        "gasPrice": "0x2127ddd32",
        "value": "0x0"
      },
      "0x98a87cc",
      {
        "tracer": "callTracer",
        "tracerConfig": {
          "onlyTopCall": false,
          "withLog": true
        }
      }
    ],
    "id": 1
  }' \
  https://evm-rpc.sei-apis.com

Common Debugging Scenarios

Transaction Reverted

Problem: Transaction failed with revert Solution: Use callTracer to find the exact revert reason

Out of Gas

Problem: Transaction ran out of gas Solution: Use gas analysis tracer to optimize gas usage

Unexpected Behavior

Problem: Transaction succeeded but wrong result Solution: Use opcode tracer for step-by-step analysis

Slow Performance

Problem: Transaction uses too much gas Solution: Use state access tracer to find inefficiencies

Quick Reference

Essential Commands

# Trace transaction
debug_traceTransaction(hash, {tracer: "callTracer"})

# Trace block
debug_traceBlockByNumber("latest", {tracer: "callTracer"})

# Simulate call
debug_traceCall(tx, "latest", {tracer: "callTracer"})

# State access
debug_traceStateAccess(hash)

# Trace transaction with timing/store-access profiling
debug_traceTransactionProfile(hash, {})

Common Tracers

• callTracer: Contract call hierarchy
• opcodeTracer: Opcode-level execution
• Custom JS: Custom analysis logic

Next Steps

1. JavaScript Tracers - Custom analysis scripts
2. Troubleshooting - Common issues and solutions

Start with callTracer for general debugging, then use specialized tracers for specific analysis needs.