Node Inspector is a debugger interface for Node.js applications that uses the Blink Developer Tools (formerly WebKit Web Inspector).
Since version 6.3, Node.js provides a built-in DevTools-based debugger which mostly deprecates Node Inspector, see e.g. this blog post to get started. The built-in debugger is developed directly by the V8/Chromium team and provides certain advanced features (e.g. long/async stack traces) that are too difficult to implement in Node Inspector.
Table of Content
$ npm install -g node-inspector
$ node-debug app.js
See available configuration options here
node-debug command will load Node Inspector in your default browser.
NOTE: Node Inspector works in Chrome and Opera only. You have to re-open the inspector page in one of those browsers if another browser is your default web browser (e.g. Safari or Internet Explorer).
Node Inspector works almost exactly as the Chrome Developer Tools. Read the excellent DevTools overview to get started.
Other useful resources:
- Documentation specific to Node Inspector provided by StrongLoop: Debugging with Node Inspector
- Miroslav's talk How to Debug Node Apps with Node Inspector
- Danny's screencasts (most likely outdated by now)
- Getting Started from scratch on wiki (most likely outdated by now)
- Navigate in your source files
- Set breakpoints (and specify trigger conditions)
- Step over, step in, step out, resume (continue)
- Inspect scopes, variables, object properties
- Hover your mouse over an expression in your source to display its value in a tooltip
- Edit variables and object properties
- Continue to location
- Break on exceptions
- Disable/enable all breakpoints
- CPU and HEAP profiling
- Network client requests inspection
- Console output inspection
- Node Inspector uses WebSockets, so no polling for breaks.
- Remote debugging and debugging remote machine.
- Live edit of running code, optionally persisting changes back to the file-system.
- Set breakpoints in files that are not loaded into V8 yet - useful for debugging module loading/initialization.
- Embeddable in other applications - see Embedding HOWTO for more details.
- Be careful about viewing the contents of Buffer objects, each byte is displayed as an individual array element; for most Buffers this will take too long to render.
- While not stopped at a breakpoint the console doesn't always behave as you might expect. See the issue #146.
- Break on uncaught exceptions does not work in all Node versions, you need at least v0.11.3 (see node#5713).
- Debugging multiple processes (e.g. cluster) is cumbersome. Read the following blog post for instructions: Debugging Clustered Apps with Node-Inspector
My script runs too fast to attach the debugger.
The debugged process must be started with
--debug-brk, this way the script is paused on the first line.
node-debug adds this option for you by default.
I got the UI in a weird state.
When in doubt, refresh the page in browser
Can I debug remotely?
Yes. Node Inspector must be running on the same machine, but your browser can be anywhere. Just make sure port 8080 is accessible.
And if Node Inspector is not running on your remote machine, you can also debug it as long as your local machine can connect it.
In this way, you must launch Node Inspector with
--no-inject which means some features are not supported such as profiling and consoling output inspection.
So how to debug remote machine with your local Node Inspector?
$ node-inspector --debug-host 192.168.0.2 --no-inject then open the url http://127.0.0.1:8080/debug?port=5858
$ node-inspector --no-inject then specify the remote machine address as a host parameter in the url e.g.) http://127.0.0.1:8080/debug?host=192.168.123.12&port=5858
How do I specify files to hide?
Create a JSON-encoded array. You must escape quote characters when using a command-line option.
$ node-inspector --hidden='["node_modules/framework"]'
Note that the array items are interpreted as regular expressions.
UI doesn't load or doesn't work and refresh didn't help
Make sure that you have adblock disabled as well as any other content blocking scripts and plugins.
How can I (selectively) delete debug session metadata?
You may want to delete debug session metadata if for example Node Inspector gets in a bad state with some watch variables that were function calls (possibly into some special c-bindings). In such cases, even restarting the application/debug session may not fix the problem.
// Remove allwindowlocalStorageclear// Or, to list keys so you can selectively remove them with removeItem()windowlocalStorage// Remove all the watch expressionswindowlocalStorage// Remove all the breakpointswindowlocalStorage
When you are done cleaning up, hit refresh in the browser.
Node Inspector takes a long time to start up.
Try setting --no-preload to true. This option disables searching disk for *.js at startup. Code will still be loaded into Node Inspector at runtime, as modules are required.
How do I debug Mocha unit-tests?
You have to start
_mocha as the debugged process and make sure
the execution pauses on the first line. This way you have enough
time to set your breakpoints before the tests are run.
$ node-debug _mocha
How do I debug Gulp tasks?
If you are running on a Unix system you can simply run the following command.
$(which ..) statement gets replaced with the full path to the gulp-cli.
$ node-debug $(which gulp) task
If you are running on Windows, you have to get the full path of
to make an equivalent command:
> node-debug %appdata%\npm\node_modules\gulp\bin\gulp.js task
You can omit the
task part to run the
node-debug is a convenient way to start your debugging
session, there may come time when you need to tweak the default setup.
There are three steps needed to get you up and debugging:
1. Start the Node Inspector server
You can leave the server running in background, it's possible to debug multiple processes using the same server instance.
2. Enable debug mode in your Node process
You can either start Node with a debug flag like:
$ node --debug your/node/program.js
or, to pause your script on the first line:
$ node --debug-brk your/short/node/script.js
Or you can enable debugging on a node that is already running by sending it a signal:
Get the PID of the node process using your favorite method.
ps -efare good$ pgrep -l node2345 node your/node/server.js
Send it the USR1 signal$ kill -s USR1 2345
Windows does not support UNIX signals. To enable debugging, you can use
an undocumented API function
Get the PID of the node process using your favorite method, e.g.> tasklist /FI "IMAGENAME eq node.exe"Image Name PID Session Name Session# Mem Usage========================= ======== ================ =========== ============node.exe 3084 Console 1 11,964 K
Call the API:> node -e "process._debugProcess(3084)"
3. Load the debugger UI
Open http://127.0.0.1:8080/?port=5858 in the Chrome browser.
node-debug use rc module
to manage configuration options.
Places for configuration:
- command line arguments (parsed by yargs)
- environment variables prefixed with
- if you passed an option
--config filethen from that file
- a local
.node-inspectorrcor the first found looking in
./ ../ ../../ ../../../etc.
All configuration sources that where found will be flattened into one object, so that sources earlier in this list override later ones.
|--help||-h||Display information about available options.
|--version||-v||Display Node Inspector's version.|
|--debug-port||-d||5858||Node/V8 debugger port.
|--web-host||0.0.0.0||Host to listen on for Node Inspector's web interface.
|--web-port||-p||8080||Port to listen on for Node Inspector's web interface.|
|--debug-brk||-b||true||Break on the first line.
|--nodejs||||Pass NodeJS options to debugged process.
|--script||||Pass options to debugged process.
|--cli||-c||false||CLI mode, do not open browser.|
|--save-live-edit||false||Save live edit changes to disk (update the edited files).|
|--preload||true||Preload *.js files. You can disable this option
to speed up the startup.
|--inject||true||Enable injection of debugger extensions into the debugged process. It's possible disable only part of injections using subkeys
|--hidden||||Array of files to hide from the UI,
breakpoints in these files will be ignored.
All paths are interpreted as regular expressions.
|--stack-trace-limit||50||Number of stack frames to show on a breakpoint.|
|--ssl-key||Path to file containing a valid SSL key.|
|--ssl-cert||Path to file containing a valid SSL certificate.|
$ node-debug [general-options] [node-debug-options] [node-inspector-options] [script]
$ node-inspector [general-options] [node-inspector-options]
Display full usage info:
$ node-debug --help -l
Set debug port of debugging process to
$ node-debug -p 5859 app
--web-host=127.0.0.2 to node-inspector. Start node-inspector to listen on
$ node-debug --web-host 127.0.0.2 app
--option=value to debugging process:
$ node-debug app --option value
Start node-inspector to listen on HTTPS:
$ node-debug --ssl-key ./ssl/key.pem --ssl-cert ./ssl/cert.pem app
Ignore breakpoints in files stored in
node_modules folder or ending in
$ node-debug --hidden node_modules/ --hidden \.test\.js$ app
--harmony flag to the node process running the debugged script:
$ node-debug --nodejs --harmony app
Disable preloading of
$ node-debug --no-preload app
Use dashed option names in RC files. Sample config file (to be saved as
"web-port": 8088"web-host": "0.0.0.0""debug-port": 5858"save-live-edit": true"preload": false"hidden": "\.test\.js$" "node_modules/""nodejs": "--harmony""stack-trace-limit": 50"ssl-key": "./ssl/key.pem""ssl-cert": "./ssl/cert.pem"
Making Node Inspector the best debugger for node.js cannot be achieved without the help of the community. The following resources should help you to get started.
- Danny Coates - the original author and a sole maintainer for several years.
- Miroslav Bajtoš - sponsored by StrongLoop, maintained Node Inspector through the Node.js 0.10 era.
- 3y3 - maintained Node Inspector in 2015-2016
Big thanks to the many contributors to the project, see Contributors on GitHub