diff --git a/README.md b/README.md
index c3df50a..e9d8cfb 100644
--- a/README.md
+++ b/README.md
@@ -31,8 +31,6 @@ targets: [
 
 Just point the `xclint` binary at your `.xcodeproj`. Check out its `-h` flag for more usage.
 
-⚠️ `.xclint.yml` support is a WIP. It does not work correctly at the moment.
-
 ```
 # xclint /path/to/MyProject.xcodeproj
 ```
@@ -40,8 +38,14 @@ Just point the `xclint` binary at your `.xcodeproj`. Check out its `-h` flag for
 This will run a default set of rules. But, you can customize its behavior with a `.xclint.yml` file. The basic structure borrows a lot from [SwiftLint](https://github.com/realm/SwiftLint).
 
 ```yaml
-embedded_build_settings: warning
-disabled_rules: ["dont", "run", "these"]
+# Some rules may not be appropriate for all projects. You must opt-in those.
+opt_in_rules:
+  - embedded_build_setting # checks for build settings in the project file
+  - groups_sorted          # checks that all group contents are alphabetically sorted
+
+# Other rules make sense for all projects by default. You must opt-out of those.
+disabled_rules:
+  - build_files_ordered. # checks that the ordering of techincally-unordered collections Xcode writes out is preserved
 ```
 
 ## Alternatives
diff --git a/Sources/XCLinting/ConfigurationFile.swift b/Sources/XCLinting/ConfigurationFile.swift
index ef689a6..d3d2c70 100644
--- a/Sources/XCLinting/ConfigurationFile.swift
+++ b/Sources/XCLinting/ConfigurationFile.swift
@@ -2,14 +2,17 @@ import Foundation
 
 public struct Configuration: Hashable {
 	public var disabledRules: Set<String>
+	public var optInRules: Set<String>
 	public var rules: [String: RuleConfiguration]
 
 	public init(
 		rules: [String: RuleConfiguration] = [:],
-		disabledRules: Set<String> = Set()
+		disabledRules: Set<String> = Set(),
+		optInRules: Set<String> = Set()
 	) {
 		self.rules = rules
 		self.disabledRules = disabledRules
+		self.optInRules = optInRules
 	}
 }
 
@@ -44,9 +47,11 @@ extension Configuration: Decodable {
 		/// Contains all the top-level well-defined keys used in a configuration file
 		enum PredefinedKeys: String {
 			case disabledRules = "disabled_rules"
+			case optInRules = "opt_in_rules"
 		}
 
 		case disabledRules
+		case optInRules
 		case ruleIdentifier(String)
 
 		init?(intValue: Int) {
@@ -57,6 +62,8 @@ extension Configuration: Decodable {
 			switch stringValue {
 			case PredefinedKeys.disabledRules.rawValue:
 				self = .disabledRules
+			case PredefinedKeys.optInRules.rawValue:
+				self = .optInRules
 			default:
 				self = .ruleIdentifier(stringValue)
 			}
@@ -66,6 +73,8 @@ extension Configuration: Decodable {
 			switch self {
 			case .disabledRules:
 				PredefinedKeys.disabledRules.rawValue
+			case .optInRules:
+				PredefinedKeys.optInRules.rawValue
 			case let .ruleIdentifier(value):
 				value
 			}
@@ -80,6 +89,7 @@ extension Configuration: Decodable {
 		let container = try decoder.container(keyedBy: CodingKeys.self)
 
 		self.disabledRules = Set()
+		self.optInRules = Set()
 
 		var decodedRules = [String: RuleConfiguration]()
 
@@ -87,6 +97,8 @@ extension Configuration: Decodable {
 			switch key {
 			case .disabledRules:
 				self.disabledRules = try container.decode(Set<String>.self, forKey: key)
+			case .optInRules:
+				self.optInRules = try container.decode(Set<String>.self, forKey: key)
 			case let .ruleIdentifier(name):
 				let ruleConfig = try container.decode(RuleConfiguration.self, forKey: key)
 
@@ -105,6 +117,12 @@ extension Configuration: Decodable {
 				throw XCLintError.unrecognizedRuleName(id)
 			}
 		}
+
+		for id in optInRules {
+			if allIdentifiers.contains(id) == false {
+				throw XCLintError.unrecognizedRuleName(id)
+			}
+		}
 	}
 }
 
@@ -112,6 +130,8 @@ extension Configuration {
 	public var enabledRules: Set<String> {
 		let defaultIdentifiers = XCLinter.defaultRuleIdentifiers
 
-		return defaultIdentifiers.subtracting(disabledRules)
+		return defaultIdentifiers
+			.union(optInRules)
+			.subtracting(disabledRules)
 	}
 }
diff --git a/Sources/XCLinting/XCLinter.swift b/Sources/XCLinting/XCLinter.swift
index 1e96556..76c4cbb 100644
--- a/Sources/XCLinting/XCLinter.swift
+++ b/Sources/XCLinting/XCLinter.swift
@@ -66,7 +66,6 @@ extension XCLinter.Environment {
 
 extension XCLinter {
 	public static let defaultRuleIdentifiers: Set<String> = [
-		"embedded_build_setting",
 		"build_files_ordered"
 	]
 
diff --git a/Tests/XCLintTests/ConfigurationFileTests.swift b/Tests/XCLintTests/ConfigurationFileTests.swift
index 21a527d..bdd7f00 100644
--- a/Tests/XCLintTests/ConfigurationFileTests.swift
+++ b/Tests/XCLintTests/ConfigurationFileTests.swift
@@ -25,6 +25,20 @@ final class ConfigurationTests: XCTestCase {
 		XCTAssertEqual(config, expected)
 	}
 
+	func testReadOptInRules() throws {
+		let string = """
+{
+	"opt_in_rules": ["a", "b", "c"]
+}
+"""
+
+		let config = try JSONDecoder().decode(Configuration.self, from: Data(string.utf8))
+
+		let expected = Configuration(optInRules: Set(["a", "b", "c"]))
+
+		XCTAssertEqual(config, expected)
+	}
+
 	func testReadRules() throws {
 		let string = """
 {