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Tenderly Simulator landing page showing the Simulate transaction button and three feature cards: Unlock the blockchain, Inspect and debug errors, Integrate in your dapp

Simulator landing: single-transaction and simulation bundle entry point with feature summary.

The Tenderly Simulator lets you run transactions against live mainnet or testnet state without broadcasting anything. You can simulate as any sender, override contract storage, fund addresses, and manipulate block context, all from the dashboard. The builder is the same whether you run one transaction or five. A single simulation is a one-step bundle. A simulation bundle is up to five steps that share state: each step sees the state changes made by the step before it.

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Layout

The builder has three regions: Session strip runs across the top. It holds defaults that apply to every step: Network, Block (defaults to Pending), and a default From address. Click Configure to set default gas, gas price, and value. Bundle rail is the left column. Each step card shows a step number, a label (New call until a contract is chosen, then ContractName · functionName), and a status badge after a run. Click a step to focus it. Drag to reorder. Use C to add a step, J/K to move between steps, and F to toggle focus mode. Focused step view is the right column. Before running, it shows the step editor. After running, it shows that step’s result: decoded output, gas used, events, state changes, and token transfers.

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Single simulations

To run a single simulation, work with the one step that opens by default. Decoded mode lets you pick a contract and function by name: Raw mode takes a target address and a 0x-prefixed hex payload directly. This is useful when you have calldata from an existing transaction or a manual encode. Click Simulate (or press ⌘↵) to run. The right panel fills with the result: function call summary, gas used, decoded output, and tabs for Events, State Changes, Fund Flow, and Gas Profiler. You can also start from an existing transaction: click Re-Simulate on any transaction detail page to load its inputs into the builder. The simulation runs on the block and timestamp of the original by default. To share a pre-filled form (for example from CI or a test report), click Copy draft link in the page header, or build the link yourself. See Prefill the Simulator with a draft link.

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Simulation bundles

A bundle runs up to five steps in sequence, sharing state. Use a bundle when the outcome of one transaction depends on a previous one, for example, an approval that enables a later transfer. Steps are added and reordered in the rail, each with its own From override and cheatcodes, and the whole bundle executes with one click of Simulate. See Simulation Bundles for building, reordering, result badges, and how bundles appear in the simulation history.
New Simulation builder showing session strip with network and block selectors, transaction parameters (From, Contract, Function), and collapsed cheatcode sections for Override gas, Fund address, Increase block, Override timestamp, State overrides, and Optional Access Lists

New Simulation form: session strip at top (Network, Block), transaction parameters on the left, and cheatcode sections below.

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Cheatcodes

Each step has a set of cheatcodes (add-ons that run immediately before the step executes). They apply to both single simulations (as step-level controls) and each step in a bundle.
Step editor showing Fund address, Override timestamp, and State overrides cheatcodes expanded

A step with Fund address, Override timestamp, and State overrides expanded. State overrides here sets a DAI ward storage slot to let the mint succeed.

For a detailed walkthrough of state overrides, including storage slot calculation, see Simulation with State Overrides.

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See also