# What MetaMask Added Protection checks, and why it costs extra gas

Canonical: https://tokenprimer.com/news/ab5ddcef-44d0-4bc9-b64f-ba3dd4a44048
Published: 2026-09-14T21:09:09.410Z
Publisher: Token Primer

MetaMask's onchain checks can reject execution that differs from its preview. Supported smart accounts still pay gas, including when a transaction reverts.

MetaMask's Added Protection checks whether a transaction executes under the conditions shown in its simulation. If execution differs, it reverts. The feature is supported by smart accounts on MetaMask Extension. [MetaMask documentation](https://support.metamask.io/manage-crypto/transactions/simulations/)

A normal preview estimates balance changes before signing. A malicious contract can recognize that test environment and behave differently when the transaction reaches the blockchain. Enforcing conditions onchain addresses that mismatch.

## Why the fee increases

The extra verification requires computation, increasing gas consumption. A reverted transaction still incurs the network fee. MetaMask says it charges no separate fee for Added Protection.

The distinction matters: a failed operation can prevent the unwanted transfer while still costing gas. [Token Primer's gas sponsorship explainer](https://tokenprimer.com/news/41ad29ad-dc73-4341-87eb-2252a2dea49f) describes a separate question, how another party can fund transaction fees.

## What to check before signing

Support depends on the account, network and contract interaction. The documentation covers token and NFT balance changes; it does not describe universal protection for every transfer. Matching a preview also does not establish that an investment or counterparty is trustworthy.

There is a privacy tradeoff. Estimated balance changes use a MetaMask server for simulation data. Disabling that feature also disables Added Protection. Check the current confirmation screen for both the protection setting and the network fee.

## Sources

- [What are transaction simulations?](https://support.metamask.io/manage-crypto/transactions/simulations/) — MetaMask
- [How gas sponsorship lets an Ethereum wallet cover your transaction fees](https://tokenprimer.com/news/41ad29ad-dc73-4341-87eb-2252a2dea49f) — Token Primer

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