diff --git a/Makefile b/Makefile
index 3f37ac5aaea..ee1c06d68c3 100644
--- a/Makefile
+++ b/Makefile
@@ -117,7 +117,7 @@ lint_yaml: normalize_yaml ## Lints YAML files
 	(! git diff --name-only | grep "^config/.*\.yml$$") || (echo "Error: Run 'make normalize_yaml' to normalize YAML"; exit 1)
 
 lint_yarn_workspaces: ## Lints Yarn workspace packages
-	scripts/validate-workspaces.js
+	scripts/validate-workspaces.mjs
 
 lint_asset_bundle_size: ## Lints JavaScript and CSS compiled bundle size
 	@# This enforces an asset size budget to ensure that download sizes are reasonable and to protect
diff --git a/app/javascript/packages/README.md b/app/javascript/packages/README.md
index e2d205b0586..a649bd7c8a1 100644
--- a/app/javascript/packages/README.md
+++ b/app/javascript/packages/README.md
@@ -2,25 +2,4 @@
 
 Packages are independent JavaScript libraries. As much as possible, their behaviors should be reusable and make no assumptions about particular application pages or configuration. Instead, they should be initialized by a [`pack`](../packs) which provides relevant configuration and page element references.
 
-A package should behave much like any other third-party [NPM package](https://www.npmjs.com/), where each folder in this directory represents a single package. These packages are managed using [Yarn workspaces](https://classic.yarnpkg.com/lang/en/docs/workspaces/).
-
-Each package should include a `package.json` with at least `name`, `version`, and `private` fields:
-
-- Name should start with `@18f/identity-` and end with the folder name
-- Version should be fixed to `1.0.0`
-- Packages should be private, since they are not published
-- Any `devDependencies` should be defined in the root project directory, not in a package
-- Define `dependencies` for any third-party libraries used in a package
-  - It is not necessary to define `dependencies` for other sibling packages
-
-**Example:**
-
-_packages/analytics/package.json_
-
-```json
-{
-  "name": "@18f/identity-analytics",
-  "version": "1.0.0",
-  "private": true
-}
-```
+A package should behave much like any other third-party [NPM package](https://www.npmjs.com/), where each folder in this directory represents a single package. These packages are managed using [Yarn workspaces](https://classic.yarnpkg.com/lang/en/docs/workspaces/). Refer to [Front-end Architecture documentation on Yarn Workspaces](https://github.com/18F/identity-idp/blob/main/docs/frontend.md#yarn-workspaces) for more information.
diff --git a/app/javascript/packages/address-search/package.json b/app/javascript/packages/address-search/package.json
index 33541701e7d..4ab55f98a1b 100644
--- a/app/javascript/packages/address-search/package.json
+++ b/app/javascript/packages/address-search/package.json
@@ -32,5 +32,6 @@
     "type": "git",
     "url": "https://github.com/18f/identity-idp.git",
     "directory": "app/javascript/packages/address-search"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/analytics/package.json b/app/javascript/packages/analytics/package.json
index 6ade5aa72c0..e13018b2865 100644
--- a/app/javascript/packages/analytics/package.json
+++ b/app/javascript/packages/analytics/package.json
@@ -1,5 +1,8 @@
 {
   "name": "@18f/identity-analytics",
   "private": true,
-  "version": "1.0.0"
+  "version": "1.0.0",
+  "sideEffects": [
+    "./click-observer-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/assets/package.json b/app/javascript/packages/assets/package.json
index e39802f92f9..23ac44a1bbe 100644
--- a/app/javascript/packages/assets/package.json
+++ b/app/javascript/packages/assets/package.json
@@ -4,5 +4,6 @@
   "version": "1.0.0",
   "peerDependencies": {
     "webpack": ">=5"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/build-sass/package.json b/app/javascript/packages/build-sass/package.json
index 27fb9961242..2941625c096 100644
--- a/app/javascript/packages/build-sass/package.json
+++ b/app/javascript/packages/build-sass/package.json
@@ -32,5 +32,6 @@
     "chokidar": "^3.5.3",
     "lightningcss": "^1.23.0",
     "sass-embedded": "^1.70.0"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/captcha-submit-button/package.json b/app/javascript/packages/captcha-submit-button/package.json
index dd41558f931..d4f99869900 100644
--- a/app/javascript/packages/captcha-submit-button/package.json
+++ b/app/javascript/packages/captcha-submit-button/package.json
@@ -1,5 +1,8 @@
 {
   "name": "@18f/identity-captcha-submit-button",
   "version": "1.0.0",
-  "private": true
+  "private": true,
+  "sideEffects": [
+    "./captcha-submit-button-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/clipboard-button/package.json b/app/javascript/packages/clipboard-button/package.json
index 8b468540391..31a34e15293 100644
--- a/app/javascript/packages/clipboard-button/package.json
+++ b/app/javascript/packages/clipboard-button/package.json
@@ -4,5 +4,8 @@
   "private": true,
   "dependencies": {
     "@18f/identity-design-system": "^8.1.2"
-  }
+  },
+  "sideEffects": [
+    "./clipboard-button-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/components/package.json b/app/javascript/packages/components/package.json
index 64ca0dfd35d..b1f4e42250b 100644
--- a/app/javascript/packages/components/package.json
+++ b/app/javascript/packages/components/package.json
@@ -32,5 +32,6 @@
     "type": "git",
     "url": "https://github.com/18f/identity-idp.git",
     "directory": "app/javascript/packages/components"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/compose-components/package.json b/app/javascript/packages/compose-components/package.json
index 8ec82d11652..29fcd9d2b79 100644
--- a/app/javascript/packages/compose-components/package.json
+++ b/app/javascript/packages/compose-components/package.json
@@ -4,5 +4,6 @@
   "version": "1.0.0",
   "dependencies": {
     "react": "^17.0.2"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/config/package.json b/app/javascript/packages/config/package.json
index c9af12df0b3..3afb193f3c8 100644
--- a/app/javascript/packages/config/package.json
+++ b/app/javascript/packages/config/package.json
@@ -1,5 +1,6 @@
 {
   "name": "@18f/identity-config",
   "private": true,
-  "version": "1.0.0"
+  "version": "1.0.0",
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/countdown/package.json b/app/javascript/packages/countdown/package.json
index 1bc751a6fc5..82526ba1386 100644
--- a/app/javascript/packages/countdown/package.json
+++ b/app/javascript/packages/countdown/package.json
@@ -1,5 +1,9 @@
 {
   "name": "@18f/identity-countdown",
   "private": true,
-  "version": "1.0.0"
+  "version": "1.0.0",
+  "sideEffects": [
+    "./countdown-alert-element.ts",
+    "./countdown-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/device/package.json b/app/javascript/packages/device/package.json
index c7d769e402f..0bb8990314e 100644
--- a/app/javascript/packages/device/package.json
+++ b/app/javascript/packages/device/package.json
@@ -1,5 +1,6 @@
 {
   "name": "@18f/identity-device",
   "private": true,
-  "version": "1.0.0"
+  "version": "1.0.0",
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/document-capture-polling/package.json b/app/javascript/packages/document-capture-polling/package.json
index 22cd45db4b9..477951beab3 100644
--- a/app/javascript/packages/document-capture-polling/package.json
+++ b/app/javascript/packages/document-capture-polling/package.json
@@ -1,5 +1,6 @@
 {
   "name": "@18f/identity-document-capture-polling",
   "private": true,
-  "version": "1.0.0"
+  "version": "1.0.0",
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/document-capture/package.json b/app/javascript/packages/document-capture/package.json
index 76877772573..0c1ca180991 100644
--- a/app/javascript/packages/document-capture/package.json
+++ b/app/javascript/packages/document-capture/package.json
@@ -6,5 +6,6 @@
     "react": "^17.0.2",
     "react-dom": "^17.0.2",
     "swr": "^2.0.0"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/eslint-plugin/package.json b/app/javascript/packages/eslint-plugin/package.json
index c9f3cdc5f20..1cb9c0e98b9 100644
--- a/app/javascript/packages/eslint-plugin/package.json
+++ b/app/javascript/packages/eslint-plugin/package.json
@@ -56,5 +56,6 @@
     "eslint-plugin-react-hooks": {
       "optional": true
     }
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/form-steps/package.json b/app/javascript/packages/form-steps/package.json
index 74a60e8e1b2..57dee9a85b8 100644
--- a/app/javascript/packages/form-steps/package.json
+++ b/app/javascript/packages/form-steps/package.json
@@ -4,5 +4,6 @@
   "private": true,
   "peerDependencies": {
     "react": "*"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/i18n/package.json b/app/javascript/packages/i18n/package.json
index 0b07c95f6f9..2af4ad53947 100644
--- a/app/javascript/packages/i18n/package.json
+++ b/app/javascript/packages/i18n/package.json
@@ -24,5 +24,6 @@
     "type": "git",
     "url": "https://github.com/18f/identity-idp.git",
     "directory": "app/javascript/packages/i18n"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/manageable-authenticator/package.json b/app/javascript/packages/manageable-authenticator/package.json
index 9d02f272dbe..1c50a094e50 100644
--- a/app/javascript/packages/manageable-authenticator/package.json
+++ b/app/javascript/packages/manageable-authenticator/package.json
@@ -1,5 +1,8 @@
 {
   "name": "@18f/identity-manageable-authenticator",
   "version": "1.0.0",
-  "private": true
+  "private": true,
+  "sideEffects": [
+    "./manageable-authenticator-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/masked-text-toggle/package.json b/app/javascript/packages/masked-text-toggle/package.json
index 6c94e97790c..03a7125541a 100644
--- a/app/javascript/packages/masked-text-toggle/package.json
+++ b/app/javascript/packages/masked-text-toggle/package.json
@@ -1,5 +1,6 @@
 {
   "name": "@18f/identity-masked-text-toggle",
   "private": true,
-  "version": "1.0.0"
+  "version": "1.0.0",
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/memorable-date/package.json b/app/javascript/packages/memorable-date/package.json
index 9a579ea5612..8f2bf2015a5 100644
--- a/app/javascript/packages/memorable-date/package.json
+++ b/app/javascript/packages/memorable-date/package.json
@@ -1,5 +1,8 @@
 {
   "name": "@18f/identity-memorable-date",
   "private": true,
-  "version": "1.0.0"
-}
\ No newline at end of file
+  "version": "1.0.0",
+  "sideEffects": [
+    "./index.ts"
+  ]
+}
diff --git a/app/javascript/packages/modal/package.json b/app/javascript/packages/modal/package.json
index e8c917ab013..abef112c26b 100644
--- a/app/javascript/packages/modal/package.json
+++ b/app/javascript/packages/modal/package.json
@@ -4,5 +4,8 @@
   "private": true,
   "dependencies": {
     "focus-trap": "^6.7.1"
-  }
+  },
+  "sideEffects": [
+    "./modal-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/normalize-yaml/package.json b/app/javascript/packages/normalize-yaml/package.json
index e9f55bb3c47..c6d186d3aab 100644
--- a/app/javascript/packages/normalize-yaml/package.json
+++ b/app/javascript/packages/normalize-yaml/package.json
@@ -39,5 +39,6 @@
   },
   "peerDependencies": {
     "prettier": ">=3"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/one-time-code-input/package.json b/app/javascript/packages/one-time-code-input/package.json
index f35d827a064..dc95624fb4a 100644
--- a/app/javascript/packages/one-time-code-input/package.json
+++ b/app/javascript/packages/one-time-code-input/package.json
@@ -1,5 +1,8 @@
 {
   "name": "@18f/identity-one-time-code-input",
   "private": true,
-  "version": "1.0.0"
+  "version": "1.0.0",
+  "sideEffects": [
+    "./one-time-code-input-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/password-confirmation/package.json b/app/javascript/packages/password-confirmation/package.json
index 3e52bad9500..fe13b63efae 100644
--- a/app/javascript/packages/password-confirmation/package.json
+++ b/app/javascript/packages/password-confirmation/package.json
@@ -1,5 +1,8 @@
 {
   "name": "@18f/identity-password-confirmation",
   "private": true,
-  "version": "1.0.0"
+  "version": "1.0.0",
+  "sideEffects": [
+    "./password-confirmation-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/password-strength/package.json b/app/javascript/packages/password-strength/package.json
index 0b364ce0299..8e38faea13f 100644
--- a/app/javascript/packages/password-strength/package.json
+++ b/app/javascript/packages/password-strength/package.json
@@ -4,5 +4,8 @@
   "version": "1.0.0",
   "dependencies": {
     "zxcvbn": "^4.4.2"
-  }
+  },
+  "sideEffects": [
+    "./password-strength-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/password-toggle/package.json b/app/javascript/packages/password-toggle/package.json
index a3daa28083e..555f2f92b4f 100644
--- a/app/javascript/packages/password-toggle/package.json
+++ b/app/javascript/packages/password-toggle/package.json
@@ -1,5 +1,8 @@
 {
   "name": "@18f/identity-password-toggle",
   "private": true,
-  "version": "1.0.0"
+  "version": "1.0.0",
+  "sideEffects": [
+    "./password-toggle-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/phone-input/package.json b/app/javascript/packages/phone-input/package.json
index 56504a875cd..0ee0ba81331 100644
--- a/app/javascript/packages/phone-input/package.json
+++ b/app/javascript/packages/phone-input/package.json
@@ -5,5 +5,8 @@
   "dependencies": {
     "intl-tel-input": "^17.0.19",
     "libphonenumber-js": "^1.10.55"
-  }
+  },
+  "sideEffects": [
+    "./index.ts"
+  ]
 }
diff --git a/app/javascript/packages/print-button/package.json b/app/javascript/packages/print-button/package.json
index 72eebb02604..b42b3597fb9 100644
--- a/app/javascript/packages/print-button/package.json
+++ b/app/javascript/packages/print-button/package.json
@@ -1,5 +1,8 @@
 {
   "name": "@18f/identity-print-button",
   "version": "1.0.0",
-  "private": true
+  "private": true,
+  "sideEffects": [
+    "./print-button-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/rails-i18n-webpack-plugin/package.json b/app/javascript/packages/rails-i18n-webpack-plugin/package.json
index 948ecbe20af..dbb6f305731 100644
--- a/app/javascript/packages/rails-i18n-webpack-plugin/package.json
+++ b/app/javascript/packages/rails-i18n-webpack-plugin/package.json
@@ -10,5 +10,8 @@
   "peerDependencies": {
     "sinon": "*",
     "webpack": ">=5"
-  }
+  },
+  "sideEffects": [
+    "./spec/**"
+  ]
 }
diff --git a/app/javascript/packages/react-hooks/package.json b/app/javascript/packages/react-hooks/package.json
index 0c7f4ca36a9..f014e531868 100644
--- a/app/javascript/packages/react-hooks/package.json
+++ b/app/javascript/packages/react-hooks/package.json
@@ -4,5 +4,6 @@
   "version": "1.0.0",
   "peerDependencies": {
     "react": ">=16.8.0"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/react-i18n/package.json b/app/javascript/packages/react-i18n/package.json
index 75371b668c6..5622f922eb6 100644
--- a/app/javascript/packages/react-i18n/package.json
+++ b/app/javascript/packages/react-i18n/package.json
@@ -4,5 +4,6 @@
   "version": "1.0.0",
   "dependencies": {
     "react": "^17.0.2"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/request/package.json b/app/javascript/packages/request/package.json
index 1a949d73073..dbc8dec4c97 100644
--- a/app/javascript/packages/request/package.json
+++ b/app/javascript/packages/request/package.json
@@ -1,5 +1,6 @@
 {
   "name": "@18f/identity-request",
   "version": "1.0.0",
-  "private": true
+  "private": true,
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/session/package.json b/app/javascript/packages/session/package.json
index 0005aa6a9b0..8790dfea903 100644
--- a/app/javascript/packages/session/package.json
+++ b/app/javascript/packages/session/package.json
@@ -1,5 +1,6 @@
 {
   "name": "@18f/identity-session",
   "version": "1.0.0",
-  "private": true
+  "private": true,
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/spinner-button/package.json b/app/javascript/packages/spinner-button/package.json
index 8d32bb8b494..b608938c6cc 100644
--- a/app/javascript/packages/spinner-button/package.json
+++ b/app/javascript/packages/spinner-button/package.json
@@ -9,5 +9,8 @@
     "react": {
       "optional": true
     }
-  }
+  },
+  "sideEffects": [
+    "./spinner-button-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/step-indicator/package.json b/app/javascript/packages/step-indicator/package.json
index c4462f305d6..bb2c3f36406 100644
--- a/app/javascript/packages/step-indicator/package.json
+++ b/app/javascript/packages/step-indicator/package.json
@@ -9,5 +9,8 @@
     "react": {
       "optional": true
     }
-  }
+  },
+  "sideEffects": [
+    "./step-indicator-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/stylelint-config/package.json b/app/javascript/packages/stylelint-config/package.json
index c8a634b13c4..62cefac4729 100644
--- a/app/javascript/packages/stylelint-config/package.json
+++ b/app/javascript/packages/stylelint-config/package.json
@@ -23,5 +23,6 @@
   "peerDependencies": {
     "prettier": ">=3.0.0",
     "stylelint": ">=15.10.0"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/submit-button/package.json b/app/javascript/packages/submit-button/package.json
index a8ce01b62ae..a99425a4a23 100644
--- a/app/javascript/packages/submit-button/package.json
+++ b/app/javascript/packages/submit-button/package.json
@@ -1,5 +1,8 @@
 {
   "name": "@18f/identity-submit-button",
   "version": "1.0.0",
-  "private": true
+  "private": true,
+  "sideEffects": [
+    "./submit-button-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/test-helpers/package.json b/app/javascript/packages/test-helpers/package.json
index f461143fe62..3c3784aa636 100644
--- a/app/javascript/packages/test-helpers/package.json
+++ b/app/javascript/packages/test-helpers/package.json
@@ -4,5 +4,6 @@
   "version": "1.0.0",
   "peerDependencies": {
     "sinon": "*"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/time-element/package.json b/app/javascript/packages/time-element/package.json
index 1e3a3231601..830da5124f2 100644
--- a/app/javascript/packages/time-element/package.json
+++ b/app/javascript/packages/time-element/package.json
@@ -2,5 +2,8 @@
   "name": "@18f/identity-time-element",
   "private": true,
   "version": "1.0.0",
-  "type": "module"
+  "type": "module",
+  "sideEffects": [
+    "./time-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/unpolyfill-webpack-plugin/package.json b/app/javascript/packages/unpolyfill-webpack-plugin/package.json
index 919749936e2..3c6086c75f6 100644
--- a/app/javascript/packages/unpolyfill-webpack-plugin/package.json
+++ b/app/javascript/packages/unpolyfill-webpack-plugin/package.json
@@ -11,5 +11,6 @@
   },
   "peerDependencies": {
     "webpack": ">=5"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/url/package.json b/app/javascript/packages/url/package.json
index 38deefef5de..4fbadaf76e8 100644
--- a/app/javascript/packages/url/package.json
+++ b/app/javascript/packages/url/package.json
@@ -1,5 +1,6 @@
 {
   "name": "@18f/identity-url",
   "version": "1.0.0",
-  "private": true
+  "private": true,
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/validated-field/package.json b/app/javascript/packages/validated-field/package.json
index b7f3f634e5d..56888c3cc41 100644
--- a/app/javascript/packages/validated-field/package.json
+++ b/app/javascript/packages/validated-field/package.json
@@ -9,5 +9,8 @@
     "react": {
       "optional": true
     }
-  }
+  },
+  "sideEffects": [
+    "./validated-field-element.ts"
+  ]
 }
diff --git a/app/javascript/packages/verify-flow/package.json b/app/javascript/packages/verify-flow/package.json
index f059daef1dc..2692e3a10ed 100644
--- a/app/javascript/packages/verify-flow/package.json
+++ b/app/javascript/packages/verify-flow/package.json
@@ -4,5 +4,6 @@
   "private": true,
   "dependencies": {
     "react": "^17.0.2"
-  }
+  },
+  "sideEffects": false
 }
diff --git a/app/javascript/packages/webauthn/package.json b/app/javascript/packages/webauthn/package.json
index 329b14b4603..ca713cade83 100644
--- a/app/javascript/packages/webauthn/package.json
+++ b/app/javascript/packages/webauthn/package.json
@@ -1,5 +1,9 @@
 {
   "name": "@18f/identity-webauthn",
   "version": "1.0.0",
-  "private": true
+  "private": true,
+  "sideEffects": [
+    "./webauthn-input-element.ts",
+    "./webauthn-verify-button-element.ts"
+  ]
 }
diff --git a/docs/frontend.md b/docs/frontend.md
index a1fc13ebe57..29d6b16630a 100644
--- a/docs/frontend.md
+++ b/docs/frontend.md
@@ -79,6 +79,7 @@ In practice:
     package is intended to be published to NPM.
   - ...a value for the `version` field, since it is required. The value value can be anything, and
     `"1.0.0"` is a good default.
+  - ...a `sideEffects` value listing files containing any side effects, used for [Webpack's Tree Shaking optimization](https://webpack.js.org/guides/tree-shaking/).
 - The package should be importable by its bare name, either with an `index.ts` or equivalent
   [package entrypoints](https://nodejs.org/api/packages.html#package-entry-points)
 
diff --git a/scripts/validate-workspaces.js b/scripts/validate-workspaces.mjs
similarity index 70%
rename from scripts/validate-workspaces.js
rename to scripts/validate-workspaces.mjs
index a9a75bc42d1..7774f39efa3 100755
--- a/scripts/validate-workspaces.js
+++ b/scripts/validate-workspaces.mjs
@@ -1,8 +1,8 @@
 #!/usr/bin/env node
 
-const { readFile, stat } = require('fs/promises');
-const { dirname, basename, join } = require('path');
-const { sync: glob } = require('fast-glob');
+import { readFile, stat } from 'node:fs/promises';
+import { dirname, basename, join, resolve, relative } from 'node:path';
+import glob from 'fast-glob';
 
 /** @typedef {[path: string, manifest: Record<string, any>]} ManifestPair */
 /** @typedef {ManifestPair[]} ManifestPairs */
@@ -43,9 +43,16 @@ function checkHaveCommonDependencyVersions(manifests) {
  */
 function checkHaveRequiredFields(manifests) {
   for (const [path, manifest] of manifests) {
-    ['name', 'version', 'private'].forEach((field) => {
+    Object.entries({
+      name: `Expected "@18f/identity-${basename(dirname(path))}".`,
+      version: '"1.0.0" is recommended for private packages.',
+      private: '`true` is recommended unless the package is intended to be published to NPM.',
+      sideEffects:
+        'This is usually `false`, unless there are files which include side effects, ' +
+        'such as custom elements registering to the custom element registry.',
+    }).forEach(([field, guidance]) => {
       if (!(field in manifest)) {
-        throw new Error(`Missing required field ${field} in ${path}`);
+        throw new Error([`Missing required field ${field} in ${path}`, guidance].join(' '));
       }
     });
   }
@@ -115,6 +122,31 @@ async function checkHaveDocumentation(manifests) {
   );
 }
 
+/**
+ * @param {ManifestPairs} manifests
+ */
+function checkPackageSideEffectsIncludesCustomElements(manifests) {
+  return Promise.all(
+    manifests.map(async ([manifestPath, manifest]) => {
+      const manifestDirectory = dirname(manifestPath);
+      const customElementPaths = await glob(join(manifestDirectory, '*-element.ts'));
+      const expectedPaths = customElementPaths.map((path) => resolve(path));
+      const actualPaths = Array.from(manifest.sideEffects).map((path) =>
+        resolve(join(manifestDirectory, path)),
+      );
+      const hasExpected = expectedPaths.every((path) => actualPaths.includes(path));
+      if (!hasExpected) {
+        throw new Error(
+          [
+            `Missing expected custom elements in ${manifestPath} sideEffects:`,
+            customElementPaths.map((path) => `./${relative(manifestDirectory, path)}`).join(', '),
+          ].join(' '),
+        );
+      }
+    }),
+  );
+}
+
 /**
  * @type {Record<string, (manifests: ManifestPairs) => void>}
  */
@@ -126,6 +158,7 @@ const CHECKS = {
   checkHaveCorrectVersion,
   checkHaveNoSiblingDependencies,
   checkHaveDocumentation,
+  checkPackageSideEffectsIncludesCustomElements,
 };
 
 /**
@@ -137,7 +170,7 @@ const EXCEPTIONS = {
   checkHaveCorrectPackageName: ['app/javascript/packages/eslint-plugin/package.json'],
 };
 
-const manifestPaths = glob('app/javascript/packages/*/package.json');
+const manifestPaths = await glob('app/javascript/packages/*/package.json');
 Promise.all(manifestPaths.map(async (path) => [path, await readFile(path, 'utf-8')]))
   .then((contents) =>
     contents.map(([path, content]) => /** @type {ManifestPair} */ ([path, JSON.parse(content)])),