diff --git a/cli/core/package.json b/cli/core/package.json
index d7300c47..351bef07 100644
--- a/cli/core/package.json
+++ b/cli/core/package.json
@@ -18,7 +18,7 @@
   "bin": {
     "repodog": "./bin/repodog.mjs"
   },
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/cli/cut/package.json b/cli/cut/package.json
index f0b7c953..02e4bbcc 100644
--- a/cli/cut/package.json
+++ b/cli/cut/package.json
@@ -12,7 +12,7 @@
   },
   "bugs": "https://github.com/badbatch/repodog/issues",
   "type": "module",
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/cli/new/_templates/pkg/library/package.ejs.t b/cli/new/_templates/pkg/library/package.ejs.t
index 2e23edd2..d0232764 100644
--- a/cli/new/_templates/pkg/library/package.ejs.t
+++ b/cli/new/_templates/pkg/library/package.ejs.t
@@ -16,7 +16,7 @@ sh: "<%= packageManager %> install"
   },
   "bugs": "<%= homepage %>/issues",
   "type": "module",
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/cli/new/_templates/repo/library/package.ejs.t b/cli/new/_templates/repo/library/package.ejs.t
index 7c20918b..4dd3abd8 100644
--- a/cli/new/_templates/repo/library/package.ejs.t
+++ b/cli/new/_templates/repo/library/package.ejs.t
@@ -15,7 +15,7 @@ sh: "<%= packageManager %> install && <%= packageManager %> add -D @repodog/cli
   },
   "bugs": "<%= homepage %>/issues",
   "type": "module",
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/cli/new/package.json b/cli/new/package.json
index e7cc751a..4a7ee823 100644
--- a/cli/new/package.json
+++ b/cli/new/package.json
@@ -12,7 +12,7 @@
   },
   "bugs": "https://github.com/badbatch/repodog/issues",
   "type": "module",
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/cli/postinstall/package.json b/cli/postinstall/package.json
index 465c1bd0..471369aa 100644
--- a/cli/postinstall/package.json
+++ b/cli/postinstall/package.json
@@ -12,7 +12,7 @@
   },
   "bugs": "https://github.com/badbatch/repodog/issues",
   "type": "module",
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/cli/publish/package.json b/cli/publish/package.json
index 73b47bad..cd0e6559 100644
--- a/cli/publish/package.json
+++ b/cli/publish/package.json
@@ -12,7 +12,7 @@
   },
   "bugs": "https://github.com/badbatch/repodog/issues",
   "type": "module",
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/cli/setup/package.json b/cli/setup/package.json
index 3d3b222e..2544a6b1 100644
--- a/cli/setup/package.json
+++ b/cli/setup/package.json
@@ -12,7 +12,7 @@
   },
   "bugs": "https://github.com/badbatch/repodog/issues",
   "type": "module",
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/cli/utils/package.json b/cli/utils/package.json
index 33bba01a..1564ddea 100644
--- a/cli/utils/package.json
+++ b/cli/utils/package.json
@@ -12,7 +12,7 @@
   },
   "bugs": "https://github.com/badbatch/repodog/issues",
   "type": "module",
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/cli/write/package.json b/cli/write/package.json
index 9198f57a..1ee4a3f0 100644
--- a/cli/write/package.json
+++ b/cli/write/package.json
@@ -12,7 +12,7 @@
   },
   "bugs": "https://github.com/badbatch/repodog/issues",
   "type": "module",
-  "main": "./dist/main/index.mjs",
+  "main": "./dist/esm/index.mjs",
   "types": "./dist/types/index.d.ts",
   "publishConfig": {
     "access": "public"
diff --git a/configs/rollup-config/README.md b/configs/rollup-config/README.md
index b7cfaaae..c5ee99b5 100644
--- a/configs/rollup-config/README.md
+++ b/configs/rollup-config/README.md
@@ -43,6 +43,10 @@ module.exports = {
 
 ### Environment variables
 
+`MODULE_SYSTEM` = `'esm' || 'cjs'`
+
+Sets `output.format`, directory name within `./dist` output, and the extension of the bundled output file. Default `'esm'`.
+
 `NODE_ENV` = `'prod' || 'production' || 'dev' || 'development'`
 
 When set to `'prod'` or `'production'`, terser mangles and compresses, the bundle analyser runs, and source maps are omitted.
diff --git a/configs/rollup-config/index.cjs b/configs/rollup-config/index.cjs
index 62a2e249..691de554 100644
--- a/configs/rollup-config/index.cjs
+++ b/configs/rollup-config/index.cjs
@@ -10,10 +10,11 @@ const { plugin: analyzer } = require('rollup-plugin-analyzer');
 const copy = require('rollup-plugin-copy');
 const sourcemaps = require('rollup-plugin-sourcemaps');
 
-const { NODE_ENV } = process.env;
+const { MODULE_SYSTEM = 'esm', NODE_ENV } = process.env;
 const isProdEnv = NODE_ENV === 'production' || NODE_ENV === 'prod';
 const packageDir = process.cwd();
 const external = id => !id.startsWith('.') && !id.startsWith('/');
+const outputExtension = MODULE_SYSTEM === 'esm' ? 'mjs' : 'cjs';
 
 const sourcemapPathTransform = sourcePath => {
   if (/node_modules/.test(sourcePath)) {
@@ -72,8 +73,8 @@ module.exports = (config = {}) => {
       }
     },
     output: {
-      file: `${packageDir}/dist/main/index.mjs`,
-      format: 'esm',
+      file: `${packageDir}/dist/${MODULE_SYSTEM}/index.${outputExtension}`,
+      format: MODULE_SYSTEM,
       sourcemap: true,
       sourcemapPathTransform,
     },
diff --git a/package.json b/package.json
index 65c36746..b08bd068 100644
--- a/package.json
+++ b/package.json
@@ -93,4 +93,4 @@
     "syncpack": "^9.8.6",
     "typescript": "^5.0.3"
   }
-}
\ No newline at end of file
+}