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Creating custom actions

• Last updated: July 17, 2025

• Read time: 3 Minutes

Custom actions are scripts that run directly from Burp Repeater to extract, transform, and analyze data. You can write your own custom actions to tailor Burp Repeater to your specific testing requirements.

Custom actions are built with Java and can be simple to write, even for beginners. Useful scripts may be as simple as a few lines of code. To help you get started, we provide:

• Built-in starter templates in the editor.
• Inline suggestions and error highlighting in the editor.
• A range of community and reference resources.

To create a new custom action:

1. [Optional] Make sure the Repeater tab contains a request / response pair that you've sent and want to test the custom action against. For more information, see How Burp selects test data.

2. In Repeater, click Custom actions. The Custom actions side panel opens.

3. Click New and select either Blank or From template. The Custom actions editor dialog opens.

4. If you selected From template, select a Custom action template from the list, then click Create using this template.

5. Write your custom action script using Java. For more information, see Writing custom actions.

6. Test the custom action using the built-in test function. For more information, see Testing custom actions.

7. [Optional] Click Save to library > Save. The custom action is saved to your Bambda library for future use across Burp.

8. Click OK.

If the custom action is error-free, it's added to the Custom actions side panel.

If errors exist, they appear in the Compilation errors panel. You'll need to fix these before you can add the custom action to the list. For more information, see Troubleshooting scripts.

Testing custom actions

When adding or editing a custom action, you can test its behavior using the built-in test function. This enables you to confirm that the action performs as expected.

To test a custom action in the Custom actions editor:

1. Review the sample message under Request. Optionally, replace it with the specific request you'd like to test the rule against.

2. Click Test. Burp runs the custom action on the sample message.

3. Review any output in the Console tab.

4. Adjust the custom action as necessary.

5. To restore the sample message, click .

How Burp selects test data

The test function automatically uses the open request, response, and HTTP service from the current Repeater tab when you open the Custom actions editor.

The HTTP service is the destination host, port and protocol. For example, https://example.com:443. If this information isn't available, Burp uses a null HTTP service instead. This can impact how your custom action behaves during testing, especially if it:

• Makes follow-up requests.

• Logs information about the target service.

• Processes messages based on host or protocol.