1.1.1 • Public • Published

Node-RED Flow Debugger

This module is a Plugin for Node-RED 2.x. It provides a flow debugger with the following features:

  • set breakpoints on node inputs or outputs
  • pause the runtime manually or when a message arrives at a breakpoint
  • once paused you can:
    • inspect the queued up messages
    • step forward individual messages
    • drop messages


Install this module in your Node-RED user directory or via the Palette Manager then restart Node-RED

npm install node-red-debugger


The Flow Debugger adds a new sidebar tab in the editor. Select it from the dropdown menu.

By default, the debugger is disabled. Click the 'disabled' toggle button to enable it.

The sidebar has two sections - a list of the breakpoints you have set and a list of any messages queued up in the runtime.

Working with breakpoints

With the debugger enabled, when you hover over a node's port a breakpoint indicator will appear. Move your mouse over the indicator and click once - it will turn solid blue and an entry will appear in the sidebar.

If you click on it again, the breakpoint will be deactivated but remain in place (light blue).

Clicking on it again will remove the breakpoint entirely (dotted outline).

You can also deactive a breakpoint using its checkbox in the sidebar, and remove it by clicking the x button.

Pausing the runtime

The runtime will by paused whenever a message arrives at an active breakpoint. You can also manually pause the runtime using the pause button in the sidebar.

Once paused, the flow will show how many messages are queued up at each node input and output. Those messages will also be listed in the sidebar - in the order the runtime will process them.

If you click the step button at the top of the sidebar, the runtime will process the next message in the list. You can step individual messages by clicking the step button that appears when you hover over the message.

You can also delete any message from the queue by clicking its delete button. This will prevent the message from passing any further in the flow.

You can click the play button to resume the flows.


  • Due to the way Subflows work, breakpoints on Subflow outputs will be ignored


  • Set conditions on individual breakpoints
  • Allow queued messages to be edited
  • Pause only selected nodes/flows/groups


This plugin has been developed using TypeScript. This means that when running from the source code rather than npm, it must first be built.

git clone
cd node-red-debugger
npm install
npm run build

This will generate all of the plugin files in the dist folder - which is where Node-RED will expect to load the files from.

Then, in your Node-RED user directory (~/.node-red) run:

npm install `<path to node-red-debugger directory>`


The Debugger sidebar will use the active Node-RED theme. For the breakpoints drawn within the flow workspace, the following CSS variables will be used if they are set by the active theme.

  • --red-ui-flow-debugger-breakpoint-fill
  • --red-ui-flow-debugger-breakpoint-stroke
  • --red-ui-flow-debugger-breakpoint-active-fill
  • --red-ui-flow-debugger-breakpoint-active-stroke
  • --red-ui-flow-debugger-breakpoint-inactive-fill
  • --red-ui-flow-debugger-breakpoint-inactive-stroke
  • --red-ui-flow-debugger-breakpoint-label
  • --red-ui-flow-debugger-breakpoint-label-active



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npm i node-red-debugger

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