Transaction insights

You can provide transaction insights in MetaMask's transaction confirmation window before a user signs a transaction. For example, you can show the user the percentage of gas fees they would pay for their transaction.

Steps

1. Request permission to display transaction insights

Request the endowment:transaction-insight permission by adding the following to your Snap's manifest file:

snap.manifest.json

"initialPermissions": {
  "endowment:transaction-insight": {}
}

If you need to receive the origin of the transaction request, add allowTransactionOrigin to the permission object, and set it to true:

snap.manifest.json

"initialPermissions": {
  "endowment:signature-insight": {
    "allowTransactionOrigin": true
  }
}

2. Implement the onTransaction entry point

Expose an onTransaction entry point, which receives a raw unsigned transaction payload, the chain ID, and the optional transaction origin. When a user submits a transaction using the MetaMask extension, MetaMask calls the onTransaction handler method.

The following is an example implementation of onTransaction:

index.ts

import type { OnTransactionHandler } from "@metamask/snaps-sdk";
import { panel, heading, text } from "@metamask/snaps-sdk";

export const onTransaction: OnTransactionHandler = async ({
  transaction,
  chainId,
  transactionOrigin,
}) => {
  const insights = /* Get insights */;
  return {
    content: panel([
      heading("My Transaction Insights"),
      text("Here are the insights:"),
      ...(insights.map((insight) => text(insight.value))),
    ]),
  };
};

The Snap tab in the transaction confirmation window displays the transaction insights:

Transaction severity level

Flask Only

This feature is experimental and only available in MetaMask Flask, the canary distribution of MetaMask.

A Snap providing transaction insights can return an optional severity level of "critical". MetaMask shows a modal with the warning before the user can confirm the transaction.

index.ts

import type { OnTransactionHandler } from "@metamask/snaps-sdk";
import { panel, heading, text } from "@metamask/snaps-sdk";

export const onTransaction: OnTransactionHandler = async ({
  transaction,
  chainId,
  transactionOrigin,
}) => {
  const insights = /* Get insights */;
  return {
    content: panel([
      heading("My Transaction Insights"),
      text("Here are the insights:"),
      ...(insights.map((insight) => text(insight.value))),
    ]),
    severity: "critical",
  };
};

Example

For a full end-to-end tutorial that walks you through creating a transaction insights Snap, see Create a Snap to calculate gas fee percentages. You can also see the @metamask/transaction-insights-example-snap package for a full example of implementing transaction insights.