See Everything a Transaction Did (debug_traceTransaction)

Why this matters

debug_traceTransaction is the single most powerful tool for understanding what a transaction actually did — every opcode, every stack frame, every state change. It's how every block explorer renders 'internal transactions' and how every security researcher reconstructs an exploit. Learning to read this output well is a 10× force multiplier for any on-chain investigation.

Demo

Get a structured trace from a real transaction and walk through it.

Try it yourself

1. Pick a recent Uniswap v2 swap tx hash and run cast run --rpc-url $RPC <tx> — observe the call tree.
2. Switch tracer from callTracer to prestateTracer on the same tx and identify every account whose storage was touched.
3. Identify the gas consumed in each subcall and find the single subcall that dominates gas (usually the SSTORE-heavy one).

References

• Geth docs — debug_traceTransaction
• Foundry book — cast run