diff --git a/.changeset/tall-countries-float.md b/.changeset/tall-countries-float.md
new file mode 100644
index 0000000000..d6c6946b7a
--- /dev/null
+++ b/.changeset/tall-countries-float.md
@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Add `"sideEffects": false` to `package.json` in frontend package templates. This can be added to existing packages using the new `yarn fix` command.
diff --git a/packages/cli/templates/default-common-plugin-package/package.json.hbs b/packages/cli/templates/default-common-plugin-package/package.json.hbs
index 844a951d05..992599ef6d 100644
--- a/packages/cli/templates/default-common-plugin-package/package.json.hbs
+++ b/packages/cli/templates/default-common-plugin-package/package.json.hbs
@@ -20,6 +20,7 @@
   "backstage": {
     "role": "common-library"
   },
+  "sideEffects": false,
   "scripts": {
     "build": "backstage-cli package build",
     "lint": "backstage-cli package lint",
diff --git a/packages/cli/templates/default-plugin/package.json.hbs b/packages/cli/templates/default-plugin/package.json.hbs
index 4e470c8c48..011a50ba37 100644
--- a/packages/cli/templates/default-plugin/package.json.hbs
+++ b/packages/cli/templates/default-plugin/package.json.hbs
@@ -18,6 +18,7 @@
   "backstage": {
     "role": "frontend-plugin"
   },
+  "sideEffects": false,
   "scripts": {
     "start": "backstage-cli package start",
     "build": "backstage-cli package build",
diff --git a/packages/cli/templates/default-react-plugin-package/package.json.hbs b/packages/cli/templates/default-react-plugin-package/package.json.hbs
index e0ee408eda..230ecc5f03 100644
--- a/packages/cli/templates/default-react-plugin-package/package.json.hbs
+++ b/packages/cli/templates/default-react-plugin-package/package.json.hbs
@@ -19,6 +19,7 @@
   "backstage": {
     "role": "web-library"
   },
+  "sideEffects": false,
   "scripts": {
     "start": "backstage-cli package start",
     "build": "backstage-cli package build",
diff --git a/packages/cli/templates/web-library-package/package.json.hbs b/packages/cli/templates/web-library-package/package.json.hbs
index 957efef167..f9f703f523 100644
--- a/packages/cli/templates/web-library-package/package.json.hbs
+++ b/packages/cli/templates/web-library-package/package.json.hbs
@@ -18,6 +18,7 @@
   "backstage": {
     "role": "web-library"
   },
+  "sideEffects": false,
   "scripts": {
     "start": "backstage-cli package start",
     "build": "backstage-cli package build",