Sigvex
EVMSimulation2 min read

Fork Sandbox

Fork a network at a chosen block, impersonate any account, and send transactions against real on-chain state — then read the receipt, gas, revert reason, and balance deltas.

Open Fork SandboxAll guides
evmsimulationforkworkspace

Fork Sandbox gives you a private copy of a network, forked at a block you choose, where you can send transactions as any address and watch exactly what happens. It runs against real on-chain state, so you can reproduce an exploit, test a fix, or probe a contract’s behaviour without touching mainnet or spending real funds.

Why it exists

Reading a contract tells you what it should do; running a transaction tells you what it does. To confirm an attack path — or to check that a proposed guard actually blocks it — you need to execute against the same state the real contract sees. A fork lets you do that safely: impersonate the attacker, send the transaction, and read the result, all in a throwaway session.

Who uses it

  • Auditor / researcher — reproduces a suspected vulnerability end-to-end and confirms whether it is exploitable.
  • Incident responder — replays an incident transaction against the forked state to understand what moved and how.

How to open it

  1. Sidebar → Simulation → Fork Sandbox.
  2. Direct URL — /sandbox.

Working in a session

  1. Create a session — pick the network and the fork block. The sandbox forks state as of that block.
  2. Hydrate a contract — point the session at a contract address so its real code and storage are loaded into the fork.
  3. Impersonate — enable sender impersonation to send a transaction as any account, with an optional minimum balance so the impersonated sender can cover value and gas.
  4. Send a transaction — supply the contract address, calldata, and value, and let gas estimate or set it yourself.
  5. Read the result — the transaction receipt, gas used, revert reason on failure, and value deltas showing which balances changed and by how much. Refresh state re-reads the fork.
  6. Destroy the session when you’re done to release the fork.

Limits

  • A session is ephemeral — state lives only for the life of the fork and is discarded on teardown.
  • The sandbox executes transactions against forked state; it is a reproduction and testing surface, not a broadcaster. Nothing you send here touches the live network.
  • Upgrade Simulator — models a proxy upgrade’s storage and selector effects.
  • Exploit Lab — turns a confirmed exploit into a sealed, reproducible capsule.