diff --git a/.all-contributorsrc b/.all-contributorsrc
index c7f04f4..9a77f61 100644
--- a/.all-contributorsrc
+++ b/.all-contributorsrc
@@ -29,6 +29,15 @@
       "contributions": [
         "test"
       ]
+    },
+    {
+      "login": "ta2edchimp",
+      "name": "Andreas Windt",
+      "avatar_url": "https://avatars1.githubusercontent.com/u/262436?v=3",
+      "html_url": "https://twitter.com/ta2edchimp",
+      "contributions": [
+        "code", "doc", "test"
+      ]
     }
   ]
 }
diff --git a/README.md b/README.md
index 395347b..8e7530a 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,14 @@ to identify built-in ESLint rules that you're not explicitly configuring.
 [![All Contributors](https://img.shields.io/badge/all_contributors-2-orange.svg?style=flat-square)](#contributors)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
+## Installation
+
+Simply install locally as a development dependency to your project's package:
+
+```
+npm install --save-dev eslint-find-new-rules
+```
+
 ## Usage
 
 The intended usage is as an npm script:
@@ -39,6 +47,8 @@ eslint-find-new-rules ./index.js
 
 This is resolved relative to the `process.cwd()` which, in the context of npm scripts is always the location of your `package.json`.
 
+You may specify any [config format supported by ESLint](http://eslint.org/docs/user-guide/configuring).
+
 ### Absolute Path
 
 You can also provide an absolute path:
@@ -47,6 +57,8 @@ You can also provide an absolute path:
 eslint-find-new-rules ~/Developer/eslint-config-kentcdodds/index.js
 ```
 
+**Please note** that any tested ESLint config file must reside below your project's root.
+
 ### Default to `main`
 
 It will also default to the `main` in your `package.json`, so you can omit the argument altogether:
@@ -72,4 +84,3 @@ Special thanks to [@mgol](https://github.com/mgol) who created the original scri
 ## LICENSE
 
 MIT
-
diff --git a/bin.js b/bin.js
index 2640074..661c9b7 100755
--- a/bin.js
+++ b/bin.js
@@ -5,10 +5,11 @@
 // Prints rules recognized by ESLint that don't appear in the given config
 // preset. It helps with upgrading the preset when new ESLint gets released.
 var path = require('path')
+var eslint = require('eslint')
 var isAbsolute = require('path-is-absolute')
 var findNewRules = require('./index')
 
-var currentRules = Object.keys(getConfig().rules)
+var currentRules = getRules()
 var newRules = findNewRules(currentRules)
 
 if (newRules.length) {
@@ -16,18 +17,41 @@ if (newRules.length) {
   process.exit(1)
 }
 
-function getConfig() {
+function resolvePackagesMain(cwd, packageFile) {
+  var packageFilePath = path.join(cwd, packageFile)
+  var packageJson = require(packageFilePath)
+  return packageJson.main
+}
+
+function getConfigFile() {
   var specifiedFile = process.argv[2]
   if (specifiedFile) {
     // this is being called like: eslint-find-new-rules eslint-config-mgol
     if (isAbsolute(specifiedFile)) {
-      return require(specifiedFile)
+      return specifiedFile
     } else {
-      return require(path.join(process.cwd(), specifiedFile))
+      return path.join(process.cwd(), specifiedFile)
     }
   } else {
     // this is not being called with an arg. Use the package.json `main`
-    return require(process.cwd())
+    return resolvePackagesMain(process.cwd(), 'package.json')
   }
 }
 
+function getConfig(file) {
+  var cliEngine = new eslint.CLIEngine({
+    // ignore any config applicable depending on the location on the filesystem
+    useEslintrc: false,
+    // point to the particular config
+    configFile: file,
+  })
+  var config = cliEngine.getConfigForFile(file)
+  return config
+}
+
+function getRules() {
+  var configFile = getConfigFile()
+  var config = getConfig(configFile)
+  var rules = Object.keys(config.rules)
+  return rules
+}
diff --git a/package.json b/package.json
index ffbc0c0..29972cf 100644
--- a/package.json
+++ b/package.json
@@ -43,6 +43,9 @@
     "semantic-release": "4.3.5",
     "validate-commit-msg": "2.4.0"
   },
+  "peerDependencies": {
+    "eslint": "^2.0.0"
+  },
   "eslintConfig": {
     "extends": "kentcdodds",
     "parserOptions": {
diff --git a/test/bin.js b/test/bin.js
index 8b2b61c..d855f8d 100644
--- a/test/bin.js
+++ b/test/bin.js
@@ -6,8 +6,10 @@ let rules = []
 const processCwd = process.cwd
 const processExit = process.exit
 const consoleLog = console.log // eslint-disable-line no-console
-const specifiedFile = './fixtures/.eslintrc'
+const noSpecifiedFile = path.resolve(process.cwd(), './fixtures/no-path')
+const specifiedFile = './fixtures/.eslintrc.js'
 const mainFile = path.join(process.cwd(), specifiedFile)
+const extendingFile = './fixtures/extending-config.json'
 const indexStub = {
   './index': () => rules,
 }
@@ -38,7 +40,7 @@ test('no new rule and relative path', () => {
 })
 
 test('no new rule and no path', () => {
-  process.cwd = () => mainFile
+  process.cwd = () => noSpecifiedFile
   proxyquire('../bin', indexStub)
 })
 
@@ -56,6 +58,12 @@ test('new rule and relative path', () => {
 
 test('new rule and no path', () => {
   rules = ['foo', 'bar', 'baz']
-  process.cwd = () => mainFile
+  process.cwd = () => noSpecifiedFile
+  proxyquire('../bin', indexStub)
+})
+
+test('new rule (extending)', () => {
+  rules = ['comma-dangle', 'no-console', 'no-alert']
+  process.argv[2] = extendingFile
   proxyquire('../bin', indexStub)
 })
diff --git a/test/fixtures/.eslintrc b/test/fixtures/.eslintrc.js
similarity index 61%
rename from test/fixtures/.eslintrc
rename to test/fixtures/.eslintrc.js
index e33e9b5..474b5cd 100644
--- a/test/fixtures/.eslintrc
+++ b/test/fixtures/.eslintrc.js
@@ -1,5 +1,5 @@
 module.exports = {
   rules: {
-    foo: true,
+    "no-console": [2],
   }
 }
diff --git a/test/fixtures/base-config.yml b/test/fixtures/base-config.yml
new file mode 100644
index 0000000..0509a62
--- /dev/null
+++ b/test/fixtures/base-config.yml
@@ -0,0 +1,5 @@
+rules:
+  no-console:
+    - 2
+  no-alert:
+    - 2
diff --git a/test/fixtures/extending-config.json b/test/fixtures/extending-config.json
new file mode 100644
index 0000000..70e88bb
--- /dev/null
+++ b/test/fixtures/extending-config.json
@@ -0,0 +1,6 @@
+{
+  "extends": "./base-config.yml",
+  "rules": {
+    "comma-dangle": [2, "never"]
+  }
+}
diff --git a/test/fixtures/no-path/index.js b/test/fixtures/no-path/index.js
new file mode 100644
index 0000000..e4b82ae
--- /dev/null
+++ b/test/fixtures/no-path/index.js
@@ -0,0 +1,5 @@
+module.exports = {
+  rules: {
+    'no-alert': [2],
+  },
+}
diff --git a/test/fixtures/no-path/package.json b/test/fixtures/no-path/package.json
new file mode 100644
index 0000000..3c2fce3
--- /dev/null
+++ b/test/fixtures/no-path/package.json
@@ -0,0 +1,12 @@
+{
+  "name": "fake-project",
+  "version": "0.0.0",
+  "description": "Simulating a project's package.json.",
+  "private": true,
+  "main": "./index.js",
+  "eslintConfig": {
+    "rules": {
+      "no-console": [2]
+    }
+  }
+}