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Safe{Wallet} simulates transactions with the Tenderly Simulation API. Built-in simulation is part of Safe Pro. On other Safe plans, the Transaction simulation check in Safe Shield shows a Set link, and queued transactions show Set up simulation, instead of a result. To simulate on any Safe plan, add your own Tenderly project in Safe’s Environment variables settings. Safe then sends every simulation request to your project, and each simulation is saved there with its full call trace.
Generating API access tokens and using the Tenderly API are available on the paid plan. To enable them for your account, contact our sales team to schedule a call and discuss upgrading your plan.

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Prerequisites

  • A Tenderly project.
  • An access token that can reach the project. A project token (One project scope) is enough.
  • A Safe account where your connected wallet is an owner.

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Build the Tenderly API URL

The Tenderly API URL field takes the full Simulation API endpoint, including the /simulate path:
Tenderly API URL
To build it, open your project in Tenderly, go to Settings, click Copy API URL next to Project Access Tokens, and add simulate to the end of the copied URL. For account my-org and project treasury, the result is https://api.tenderly.co/api/v1/account/my-org/project/treasury/simulate.
Copy API URL copies the base project URL, which ends at /project/{project_slug}/. Safe sends requests to the exact URL you enter, so the base URL without simulate makes every simulation fail.

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Add your Tenderly project in Safe{Wallet} settings

  1. In Safe{Wallet}, open Settings and select the Environment variables tab. The Set and Set up simulation links open the same page.
  2. Under Tenderly, paste the URL from the previous section into Tenderly API URL.
  3. Paste your access token into Tenderly access token.
  4. Click Save. Safe reloads the page and applies the settings.
Safe{Wallet} Environment variables settings with the Tenderly API URL ending in /simulate and a masked access token

Tenderly API URL and access token in Safe{Wallet} Environment variables

Fill in both fields. Safe uses your project only when both the URL and the access token are set. Safe stores the values in your browser’s local storage. They apply to every Safe and network you open in that browser, so repeat the setup in each browser you use. To return to the defaults, click the reset icon in each field and click Save.

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Run a Safe transaction simulation

  1. In Safe{Wallet}, click New transaction, set up the transaction, and click Next. The Confirm transaction screen opens with the Safe Shield panel on the right.
  2. Next to Transaction simulation, click Run.
  3. The check changes to Simulation successful or Simulation failed. Click View to open the simulation in your Tenderly project.
Safe{Wallet} Confirm transaction screen with Safe Shield showing Simulation successful and a View link

Safe Shield with a successful simulation and the View link

To simulate a transaction that is already queued, open Transactions, expand the transaction in the Queue tab, and click Simulate. The View link opens https://dashboard.tenderly.co/{account_slug}/{project_slug}/simulator/{simulation_id}, where you can inspect the call trace, state changes, and events of the simulated execTransaction call.

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What Safe sends to the Simulation API

Safe sends a POST request to the Tenderly API URL with the access token in the X-Access-Key header. The request body is a single simulation of the Safe’s execTransaction call (or a multiSend call for batches) with these settings:

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Troubleshooting: Error while simulating

When the Simulation API returns an error, Safe shows Error while simulating in the transaction queue and Simulation failed in Safe Shield, without the error details. To see the actual response:
  1. Open your browser’s developer tools and select the Network tab.
  2. Run the simulation again.
  3. Select the request sent to api.tenderly.co and read its status code and response body.
If no request reaches api.tenderly.co, check that both fields are saved: Safe shows the Set link until the URL and the access token are both set.