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Custom actions
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Last updated: June 12, 2025
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Read time: 4 Minutes
Custom actions are tasks that you can apply to HTTP messages in Burp Repeater to extract, analyze, and transform data.
Custom actions are powered by Bambdas, which are snippets of code that run directly from Burp Suite's interface.
You can use custom actions to:
Analyze responses - Extract data, count elements, decode and encode message content, and check for specific content.
Retrieve additional data - Perform lookups, resolve hostnames, fetch external data, and use this data to modify the request or response.
Resend requests - Modify headers, parameters, or body content and resend the request.
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AI-powered custom actions
Custom actions can include advanced AI features, enabling real-time analysis and context-aware responses. All AI interactions are securely handled through PortSwigger's AI platform.
To use AI-powered custom actions, make sure you have enabled AI in Burp. To do this, go to Settings > AI and select Enable AI features.
Using AI features requires AI credits, with costs varying depending on the number and complexity of the AI requests needed. You can buy AI credits from your PortSwigger account and check your balance by clicking the AI icon in the bottom-right corner of Burp.
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Adding custom actions
You can add Bambdas to the Custom actions side panel in Repeater in the following ways:
Load existing Bambdas - Load Bambdas from your Bambda library. To start populating your library, you can download and import Bambdas from our GitHub repository. For more information, see Importing Bambdas.
Create new Bambdas - Write your own custom action Bambdas.
Add sample Bambdas - If the Custom actions panel is empty, click Add samples to load a set of example Bambdas that you can try out.
Loading Bambdas from your library
You can load previously saved Bambdas from your Bambda library into the Custom actions side panel.
To load a Bambda from your library:
In Repeater, click Custom actions to open the Custom actions side panel.
Click Load.
Select a recent Bambda from the list.
If the Bambda you want to load isn't in the list, click View all to view all Bambdas stored in your library.
Select a Bambda.
Click Load.
If the Bambda is error-free, it's added to the Custom actions side panel, ready for use.
Burp displays any errors in the Compilation errors panel of the Custom actions editor. You'll need to fix these before you can add the Bambda to the Custom actions side panel. For more information, see Troubleshooting Bambdas.
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To add Bambdas to your library, you can import Bambdas that have been shared with you or downloaded from our GitHub repo. For more information, see Importing Bambdas into your Bambda library.
Creating Bambdas
You can write your own custom action Bambdas to meet your specific requirements.
Related pages
- For more information on creating custom actions in Burp, see Creating custom actions.
- To learn how to write your first custom action, see our Custom action worked example.
- To view building block examples of custom actions, see our Custom actions reference guide.
- To learn how to add AI-features to your custom actions, see Developing AI features in custom actions.
- To view examples of custom actions that have been created by the community, see our Bambdas GitHub repository - Custom actions.
Running custom actions
From the Custom actions side panel, you can run Bambdas manually and configure them to run automatically after a response has been received for a sent request. Your custom action Bambdas are available from any Repeater tab.
You can apply custom action Bambdas in the following ways:
Run - Click to run the Bambda manually.
Auto-run on send - Click to enable auto-run. The Bambda runs when Burp receives a response to a request sent from that Repeater tab.
Bambda output is shown in the Output panel. To clear the output, click Clear.
Managing custom actions
You can manage your custom actions Bambdas from the Custom actions side panel:
Edit - Click beside the Bambda you want to edit.
Rename - Right-click the Bambda, then select Rename.
Save a Bambda to your library - Right-click the Bambda, then select Save to library to store it in your Bambda library.
Save a copy of a Bambda to your library - Right-click the Bambda, then select Save copy to library. A copy of the Bambda is saved to your library. This replaces the original Bambda in the Custom actions panel.
Remove from list - Right-click a Bambda that is saved in your library, then select Remove from list. The Bambda is removed from the Custom actions side panel but remains in your library for future use.
Delete - Right-click a Bambda that isn't saved in your library, then select Delete. This permanently removes the Bambda.