Project · EVM Trace Walkthrough

Hints

Use either cast run (Foundry), debug_traceTransaction directly, or Tenderly to obtain the trace. Tenderly's UI is the friendliest for first-time tracing.

For unverified contracts, decompile the bytecode with Dedaub or evm.codes Playground to make the trace readable.

Look for surprising gas costs first — they almost always point to an SSTORE on a cold storage slot or an expensive LOG operation.

Expected output

Tx: 0xabc...def
Block: 19,123,456 | Gas used: 142,371 / 200,000

Top-level call:
  CALL UniswapV3Router.exactInputSingle(...)  Gas: 142k

  Subcall 1: CALL WETH9.transferFrom(user, router, 1e18)  Gas: 51,200
    - SLOAD allowances[user][router]: 2,100 (cold)
    - SSTORE allowances[user][router] -= amount: 5,000 (update)
    - SLOAD balances[user]: 2,100 (cold)
    - SSTORE balances[user] -= amount: 5,000
    - SSTORE balances[router] += amount: 22,100 (new slot)
    - LOG3 Transfer: 1,800
  ...

Optimization observations:

1. balances[router] is created cold (22k) — pre-warming via access list saves 20k.
2. Two SLOADs on user balance/allowance could be batched into one slot-pack read.
3. The router stores nothing of its own across this trace, so its storage layout is irrelevant — but if it did, it would benefit from packing the configured fees into a single uint256.

Stretch goals

• Use prestateTracer to extract the contract's storage layout pre and post and produce a diff.
• Compare the same workflow against a Tenderly Web Trace and note which UI features (gas profiler, state-diff viewer) you wished cast had.
• For any unverified contracts in the trace, run Dedaub decompilation and verify your annotations match the decompiled source.