Speed up your AEM front-end development using aemsync, BrowserSync and this.
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Speed up your AEM front-end development using aemfed. Powered by aemsync, Browsersync and Sling Log Tracer.

Demo of aemfed changing some styling in the WKND project

aemfed doing its thing: listening for file changes, uploading them to the running AEM instance, triggering a refresh of the styling in the browser, showing AEM error messages with a reference to the issue in the local file, all within a minute (disclaimer: this is a special branch of the WKND project, optimized for the aemfed workflow).



  • Watches changes in files and uploads them to AEM using aemsync
  • Determines which clientlibs are affected by the uploaded changes
  • Runs Browsersync in proxy modus so it can communicate with all open instances of your site without any browser plugins. It reloads these pages when the changes have been uploaded, or it only injects the new styling when only styling changes were made, maintaining the state of the page.
  • Show serverside errors related to clientlibs for each request (so no more digging in the error.log to see why your styling changes won't show up). It captures errors related to HTL templates, JSP files, Less compilation, Javascript minification (YUI and GCC), .content.xml, etc.
  • If the error messages contain references to nodes in the jcr, it tries to translate them back to the files on your local file system, so you can navigate directly to the file, line and column mentioned in the error (if your IDE/shell supports the pattern).


If you don't have a package.json (npm configuration file) for your project, you probably want to install aemfed globally:

npm install aemfed --global

When using a global install with PowerShell on Windows, please check the Issues section for the limitations.

If you do have a package.json for your project, you can add it as a dev dependency:

npm install aemfed --save-dev


Start with a global install

The following commands are for the global install option (used --global).

Show the available options:

aemfed -h

Run with specific server, ignore pattern (to ignore IntelliJ temp files) and folder to watch (at the moment this has to be the actual jcr_root folder for your project):

aemfed -t "http://admin:admin@localhost:4502" -w "ui.apps/src/main/content/jcr_root/"

Start with a package.json install

The following commands are for a package.json install. Since aemfed is only available for this project and not globally, we can not use the aemfed command directly. You can use npx to run modules only available for a specific project.

Show the available options:

npx aemfed -h

When npx is not available, install it with:

npm install npx --global

Since you already have a package.json in your project, adding the startup command as a script is probably the easiest way to run aemfed (make sure the quotes in the command are escaped):

"devDependencies": {
  "aemfed": "^0.1.0"
"scripts": {
    "aemfed": "aemfed -t \"http://admin:admin@localhost:4502\" -w \"ui.apps/src/main/content/jcr_root/\""

...and run it with

npm run aemfed

Working with your codebase

Once started, the BrowserSync module will show the urls for the proxy that enables the auto reloading etc (when using aemfed these message use color, making them a lot clearer):

[Browsersync] Proxying: http://localhost:4502
[Browsersync] Access URLs:
       Local: http://localhost:3000
          UI: http://localhost:3001
 UI External:

If you connect your browsers to the Local or External Access URL, the Browsersync reload script will be injected into the pages you visit, allowing aemfed to reload pages automatically after changes have been uploaded to AEM.

Navigate to the page you want to work on and make some changes to the clientlib files under the path provided during startup. When saving the file, aemfed reports the detected file changes:

ADD jcr_root/apps/wknd/components/content/list/clientlib/less/styles/default.less

...and uploads them to AEM:

  Deploying to [localhost:4502] in 39 ms at 2018-06-18T19:03:03.273Z: OK

When the upload is done, aemfed will determine which clientlibs need a reload. It also determines if a full reload of the page is needed (javascript, html, .content.xml) or if the changes can be injected w/o a complete reload (css and in the future probably static resources like images):

[localhost:4502] Only styling was changed, try to inject
[Browsersync] File event [change] : /apps/wknd/clientlibs/clientlib-base.css
[Browsersync] File event [change] : /apps/wknd/components/content/list/clientlib.css

If the changes can be injected, a list of all clientlibs that use the changed files is send to the listening browsers. The reloading script will determine which files are present in the current page and will refresh only those resources.


When the correct version of the Sling Log Tracer is installed (see Requirements for details), aemfed is able to intercept a number of the front end related errors generated by AEM (Less, javascript, HTL, .content.xml, etc).

It shows the request that triggered the error:

[localhost:4502] Tracer output for [/etc.clientlibs/wknd/clientlibs/clientlib-base.css?browsersync=
1530965506424] (62c5e8ac-69e9-491c-8658-2bbed119d0c2)

...the error message itself:

[ERROR] LessCompilerImpl: failed to compile less /apps/wknd/components/content/list/clientlib/less/
list.less: NameError: variable @brand-secondary2 is undefined in /apps/wknd/components/content/list
/clientlib/less/styles/default.less on line 17, column 25:
16         &:hover {
17             background: @brand-secondary2;
18         }

...and an attempt to map the location in the error back to the local development environment:

Local source: ui.apps/src/main/content/jcr_root/apps/wknd/components/content/list/clientlib/less/st

Most of these errors show up only once after the file has been changed, since AEM caches the result, so its best to keep the aemfed terminal always in clear view (using the terminal in your IDE is a good way to make sure this is the case).

The Local source: line in the output, is aemfed's attempt to translate the AEM error location back to the local file, line and column. So locating the issue becomes much easier. Some IDE's and shells even recognize the pattern and turn it into a link, to make your life even easier.

Synchronize browsers

Using Browsersync it is possible to refresh content in all the browsers that connect to its local or external access urls. This includes phones and tablets, as long as they are on the same network and the external port used by Browsersync is open (not blocked by a firewall).

Connecting mobile devices can be a drag, since you have to type in the machine name or ip, port and probably part of the path to the page you're interested in, all on the tiny onscreen keyboard.

To speedup developing and testing on mobile devices, a QR code can be generated from the browser console, using the command qr(). The QR code will contain the external access url and path for the active page in the browser. Scan the QR code with the device, login to AEM if needed, and see all of you changes immediately on mobile devices too.


  • Runs on macOS, Linux and Windows
  • Works best with a recent version of node/npm, but tested with node 6.15 LTS
  • Tested on AEM 6.1, 6.2, 6.3 and 6.4
  • To be able to see the error messages from AEM, at least version 1.0.0 of the Sling Log Tracer is needed. AEM 6.2 and before have an older version or don't have the bundle at all. Versions of Log Tracer since 1.0.2 can also be installed on those older versions of AEM (6.0+ according to the ticket). See Updating Sling Log Tracer for instructions.

Updating Sling Log Tracer

  1. Check the current version of your Sling Log Tracer at /system/console/bundles/org.apache.sling.tracer on the instance you're using. If it is 1.0.0 or newer you are good. If it is 0.0.2 or the bundle is not found at all, you need to install a newer version:
  2. Download the latest Log Tracer bundle from the Sling downloads section (Sling Components > Log Tracer): https://sling.apache.org/downloads.cgi
  3. Go to /system/console/bundles on the instance you want to update and click Install/Update... in the top right corner
  4. Check Start Bundle and Refresh Packages, browse for the package downloaded in step 2 and click Install or Update
  5. Check if the install was successful by checking the version number again: /system/console/bundles/org.apache.sling.tracer
  6. Enable the Log Tracer by checking Enabled and Recording Servlet Enabled in the Tracer configuration: /system/console/configMgr/org.apache.sling.tracer.internal.LogTracer
  7. Test if the tracer is working, for example by using a non-existent variable in your Less, saving the file and making sure the page including the clietlib with the Less file is reloaded (since the clientlib errors are only triggered on a rebuild and a rebuild is only triggered when a page that uses the clientlib is requested again)


  • aemsync does not respect your projects filter.xml, so please be very careful when removing high level items when running aemfed. Changes to root nodes like /apps, /content and /etc are skipped, but when you remove /etc/clientlibs from your project (for example after you moved all your clientlibs to proxies in /apps) it does exactly that...
  • Using ~ (homedir) in paths to watch does not work as expected when aemfed does all the path processing (paths are surrounded with quotes)
  • When using aemfed globally or with npx in PowerShell on Windows, the provided parameters can not contain certain characters (for example | in an exclusion pattern), even when they are wrapped in quotes. On Windows global nodejs calls work with a wrapper CMD script and PowerShell uses slightly different escaping. Fixes: remove or rewrite parameters w/o problematic characters, use the good old cmd.exe, don't use global calls but add it as a script to a package.json, or write a custom ps1 script to handle this scenario.
  • YUI minification generates errors for each request if there is an error (Less and GCC generate errors only first time after a resource was changed)
  • When installing the WKND tutorial in a clean AEM 6.3 SP2 or AEM 6.4, it is possible the changes pushed to AEM are not present in the final clientlibs loaded into the pages. Performing a one time clientlib rebuild could fix this: http://localhost:4502/libs/granite/ui/content/dumplibs.rebuild.html and click 'Invalidate Caches' & 'Rebuild Libraries' (last step can take up to 15 minutes)
  • When inspecting Less imports to determine dependencies, very simple logic is used to process the file locations in the @import. Resulting in a number of edge cases not working as expected (and throw ENOENT exceptions):
    • Less variables are not supported in @import (used for example in the WKND tutorial in ui.apps/src/main/content/jcr_root/apps/wknd/clientlibs/clientlib-site/site/css/grid.less to switch between the 6.3 and 6.4 grid-base). As a result changes in the imported file may not trigger an update in the browser
    • Importing css files in a Less file using @import doesn't work, since it appends .less to all @imports. But since the css probably doesn't need any Less processing anyway, it is better to include it directly in a css.txt (in older versions of AEM it also speeds up the Less processing)
  • aemfed mentions there is an update and it can be installed using npm i aemfed but when I run the command nothing happens? Because the version numbers are still < 1.0.0, the default update behavior is more conservative, see npm-semver - Caret Ranges ^1.2.3 ^0.2.5 ^0.0.4 for more details. For now run npm i aemfed@latest to force an update.
  • The new log processing code is all over the place, needs it own module(s).
  • Found another issue? Please report it on GitHub: Issues


Some of the projects using it:



Thanks to the Browsersync team, to gavoja for aemsync and kevinweber for aem-front.