diff --git a/.github/workflows/commit-ci.yml b/.github/workflows/commit-ci.yml
index e2bd4be61..828146722 100644
--- a/.github/workflows/commit-ci.yml
+++ b/.github/workflows/commit-ci.yml
@@ -3,6 +3,8 @@ on:
   push:
     branches:
       - '*'
+    paths:
+      - 'sources/**'
 jobs:
   build:
     runs-on: macos-14
@@ -12,6 +14,12 @@ jobs:
         with:
           submodules: true
 
+      - name: Install SwiftLint
+        run: brew install swiftlint
+
+      - name: Lint
+        run: swiftlint
+
       - name: Configure build environment
         run: |
           echo git_ref_name="$(git describe --always)" >> $GITHUB_ENV
@@ -19,6 +27,12 @@ jobs:
       - name: Build Squirrel
         run: ./action-build.sh package
 
+      - name: Install periphery
+        run: brew install peripheryapp/periphery/periphery
+
+      - name: Check Unused Code
+        run: periphery scan
+
       - name: Upload Squirrel artifact
         uses: actions/upload-artifact@v4
         with:
diff --git a/.github/workflows/pull-request-ci.yml b/.github/workflows/pull-request-ci.yml
index 43200eb2c..408d07e88 100644
--- a/.github/workflows/pull-request-ci.yml
+++ b/.github/workflows/pull-request-ci.yml
@@ -9,6 +9,12 @@ jobs:
         with:
           submodules: true
 
+      - name: Install SwiftLint
+        run: brew install swiftlint
+
+      - name: Lint
+        run: swiftlint
+
       - name: Configure build environment
         run: |
           echo git_ref_name="$(git describe --always)" >> $GITHUB_ENV
@@ -16,6 +22,12 @@ jobs:
       - name: Build Squirrel
         run: ./action-build.sh package
 
+      - name: Install periphery
+        run: brew install peripheryapp/periphery/periphery
+
+      - name: Check Unused Code
+        run: periphery scan
+
       - name: Upload Squirrel artifact
         uses: actions/upload-artifact@v4
         with:
diff --git a/.github/workflows/release-ci.yml b/.github/workflows/release-ci.yml
index 3486eb631..044fb8637 100644
--- a/.github/workflows/release-ci.yml
+++ b/.github/workflows/release-ci.yml
@@ -5,6 +5,8 @@ on:
       - '*'
     branches:
       - master
+    paths:
+      - 'sources/**'
   workflow_dispatch:
 
 jobs:
@@ -19,9 +21,21 @@ jobs:
           fetch-depth: 0
           submodules: true
 
+      - name: Install SwiftLint
+        run: brew install swiftlint
+
+      - name: Lint
+        run: swiftlint
+
       - name: Build Squirrel
         run: ./action-build.sh archive
 
+      - name: Install periphery
+        run: brew install peripheryapp/periphery/periphery
+
+      - name: Check Unused Code
+        run: periphery scan
+
       - name: Build changelog
         id: release_log
         run: |
diff --git a/.periphery.yml b/.periphery.yml
new file mode 100644
index 000000000..a1842cba7
--- /dev/null
+++ b/.periphery.yml
@@ -0,0 +1,5 @@
+project: Squirrel.xcodeproj
+schemes:
+- Squirrel
+targets:
+- Squirrel
diff --git a/.swiftlint.yml b/.swiftlint.yml
new file mode 100644
index 000000000..55bd033cb
--- /dev/null
+++ b/.swiftlint.yml
@@ -0,0 +1,56 @@
+# By default, SwiftLint uses a set of sensible default rules you can adjust:
+disabled_rules: # rule identifiers turned on by default to exclude from running
+  - force_cast
+  - force_try
+  - todo
+opt_in_rules: # some rules are turned off by default, so you need to opt-in
+
+# Alternatively, specify all rules explicitly by uncommenting this option:
+# only_rules: # delete `disabled_rules` & `opt_in_rules` if using this
+#   - empty_parameters
+#   - vertical_whitespace
+
+analyzer_rules: # rules run by `swiftlint analyze`
+  - explicit_self
+
+included: # case-sensitive paths to include during linting. `--path` is ignored if present
+  - sources
+excluded: # case-sensitive paths to ignore during linting. Takes precedence over `included`
+
+# If true, SwiftLint will not fail if no lintable files are found.
+allow_zero_lintable_files: false
+
+# If true, SwiftLint will treat all warnings as errors.
+strict: false
+
+# rules that have both warning and error levels, can set just the warning level
+# implicitly
+line_length: 200
+function_body_length: 200
+# they can set both implicitly with an array
+type_body_length:
+  - 300 # warning
+  - 400 # error
+# or they can set both explicitly
+file_length:
+  warning: 800
+  error: 1200
+# naming rules can set warnings/errors for min_length and max_length
+# additionally they can set excluded names
+type_name:
+  min_length: 4 # only warning
+  max_length: # warning and error
+    warning: 40
+    error: 50
+  excluded: # excluded via string
+  allowed_symbols: ["_"] # these are allowed in type names
+identifier_name:
+  min_length: # only min_length
+    warning: 3
+    error: 2
+  excluded: [i, URL, of, by] # excluded via string array
+large_tuple:
+  warning: 3
+  warning: 5
+reporter: "github-actions-logging" # reporter type (xcode, json, csv, checkstyle, codeclimate, junit, html, emoji, sonarqube, markdown, github-actions-logging, summary)
+
diff --git a/sources/BridgingFunctions.swift b/sources/BridgingFunctions.swift
index 7c3d40930..ed537b3e7 100644
--- a/sources/BridgingFunctions.swift
+++ b/sources/BridgingFunctions.swift
@@ -8,7 +8,8 @@
 import Foundation
 
 protocol DataSizeable {
-    var data_size: Int32 { get set }
+  // swiftlint:disable:next identifier_name
+  var data_size: Int32 { get set }
 }
 
 extension RimeContext_stdbool: DataSizeable {}
@@ -37,7 +38,7 @@ extension DataSizeable {
       let mutableCStr = strdup(cStr)
       // Free the existing string if there is one
       if let existing = self[keyPath: keypath] {
-          free(UnsafeMutableRawPointer(mutating: existing))
+        free(UnsafeMutableRawPointer(mutating: existing))
       }
       self[keyPath: keypath] = UnsafePointer(mutableCStr)
     }
@@ -45,11 +46,13 @@ extension DataSizeable {
 }
 
 infix operator ?= : AssignmentPrecedence
+// swiftlint:disable:next operator_whitespace
 func ?=<T>(left: inout T, right: T?) {
   if let right = right {
     left = right
   }
 }
+// swiftlint:disable:next operator_whitespace
 func ?=<T>(left: inout T?, right: T?) {
   if let right = right {
     left = right
diff --git a/sources/InputSource.swift b/sources/InputSource.swift
index cf96eda89..a0c80add3 100644
--- a/sources/InputSource.swift
+++ b/sources/InputSource.swift
@@ -80,8 +80,8 @@ final class SquirrelInstaller {
     }
     for (mode, inputSource) in getInputSource(modes: [modeToSelect]) {
       if let enabled = getBool(for: inputSource, key: kTISPropertyInputSourceIsEnabled),
-          let selectable = getBool(for: inputSource, key: kTISPropertyInputSourceIsSelectCapable),
-          let selected = getBool(for: inputSource, key: kTISPropertyInputSourceIsSelected),
+         let selectable = getBool(for: inputSource, key: kTISPropertyInputSourceIsSelectCapable),
+         let selected = getBool(for: inputSource, key: kTISPropertyInputSourceIsSelected),
          enabled && selectable && !selected {
         let error = TISSelectInputSource(inputSource)
         print("Selection \(error == noErr ? "succeeds" : "fails") for input source: \(mode.rawValue)")
diff --git a/sources/MacOSKeyCodes.swift b/sources/MacOSKeyCodes.swift
index 5cf3ca5ac..ef99be00f 100644
--- a/sources/MacOSKeyCodes.swift
+++ b/sources/MacOSKeyCodes.swift
@@ -1,5 +1,5 @@
 //
-//  MacOSKeyCOdes.swift
+//  MacOSKeyCodes.swift
 //  Squirrel
 //
 //  Created by Leo Liu on 5/9/24.
diff --git a/sources/Main.swift b/sources/Main.swift
index 005593681..3c54a7044 100644
--- a/sources/Main.swift
+++ b/sources/Main.swift
@@ -10,8 +10,8 @@ import InputMethodKit
 
 @main
 struct SquirrelApp {
-  static let userDir = if let pw = getpwuid(getuid()) {
-    URL(fileURLWithFileSystemRepresentation: pw.pointee.pw_dir, isDirectory: true, relativeTo: nil).appending(components: "Library", "Rime")
+  static let userDir = if let pwuid = getpwuid(getuid()) {
+    URL(fileURLWithFileSystemRepresentation: pwuid.pointee.pw_dir, isDirectory: true, relativeTo: nil).appending(components: "Library", "Rime")
   } else {
     try! FileManager.default.url(for: .libraryDirectory, in: .userDomainMask, appropriateFor: nil, create: false).appendingPathComponent("Rime", isDirectory: true)
   }
@@ -19,6 +19,7 @@ struct SquirrelApp {
     URL(fileURLWithFileSystemRepresentation: dir, isDirectory: false, relativeTo: nil)
   }
 
+  // swiftlint:disable:next cyclomatic_complexity
   static func main() {
     let rimeAPI: RimeApi_stdbool = rime_get_api_stdbool().pointee
 
diff --git a/sources/SquirrelApplicationDelegate.swift b/sources/SquirrelApplicationDelegate.swift
index ff674b725..a80d7e1d9 100644
--- a/sources/SquirrelApplicationDelegate.swift
+++ b/sources/SquirrelApplicationDelegate.swift
@@ -58,6 +58,7 @@ final class SquirrelApplicationDelegate: NSObject, NSApplicationDelegate, SPUSta
   }
 
   func applicationWillTerminate(_ notification: Notification) {
+    // swiftlint:disable:next notification_center_detachment
     NotificationCenter.default.removeObserver(self)
     DistributedNotificationCenter.default().removeObserver(self)
     panel?.hide()
@@ -132,8 +133,10 @@ final class SquirrelApplicationDelegate: NSObject, NSApplicationDelegate, SPUSta
         print("Error creating user data directory: \(userDataDir.path())")
       }
     }
+    // swiftlint:disable identifier_name
     let notification_handler: @convention(c) (UnsafeMutableRawPointer?, RimeSessionId, UnsafePointer<CChar>?, UnsafePointer<CChar>?) -> Void = notificationHandler
     let context_object = Unmanaged.passUnretained(self).toOpaque()
+    // swiftlint:enable identifier_name
     rimeAPI.set_notification_handler(notification_handler, context_object)
 
     var squirrelTraits = RimeTraits.rimeStructInit()
diff --git a/sources/SquirrelConfig.swift b/sources/SquirrelConfig.swift
index 65d5d7abd..75b0eeb79 100644
--- a/sources/SquirrelConfig.swift
+++ b/sources/SquirrelConfig.swift
@@ -130,7 +130,7 @@ final class SquirrelConfig {
 
   // isVertical
   func updateTextOrientation(prefix: String) -> Bool {
-  let textOrientation = getString("\(prefix)/text_orientation")
+    let textOrientation = getString("\(prefix)/text_orientation")
     switch textOrientation {
     case "horizontal":
       return false
diff --git a/sources/SquirrelInputController.swift b/sources/SquirrelInputController.swift
index 6d47f16b8..df7aba759 100644
--- a/sources/SquirrelInputController.swift
+++ b/sources/SquirrelInputController.swift
@@ -28,6 +28,7 @@ final class SquirrelInputController: IMKInputController {
   private var chordDuration: TimeInterval = 0
   private var currentApp: String = ""
 
+  // swiftlint:disable:next cyclomatic_complexity
   override func handle(_ event: NSEvent!, client sender: Any!) -> Bool {
     let modifiers = event.modifierFlags
     let changes = lastModifiers.symmetricDifference(modifiers)
@@ -128,6 +129,7 @@ final class SquirrelInputController: IMKInputController {
     return success
   }
 
+  // swiftlint:disable:next identifier_name
   func page(up: Bool) -> Bool {
     var handled = false
     handled = rimeAPI.change_page(session, up)
@@ -282,7 +284,8 @@ private extension SquirrelInputController {
     if chordKeyCount > 0 && session != 0 {
       // simulate key-ups
       for i in 0..<chordKeyCount {
-        if rimeAPI.process_key(session, Int32(chordKeyCodes[i]), Int32(chordModifiers[i] | kReleaseMask.rawValue)) {
+        let handled = rimeAPI.process_key(session, Int32(chordKeyCodes[i]), Int32(chordModifiers[i] | kReleaseMask.rawValue))
+        if handled {
           processedKeys = true
         }
       }
@@ -413,6 +416,7 @@ private extension SquirrelInputController {
     }
   }
 
+  // swiftlint:disable:next cyclomatic_complexity
   func rimeUpdate() {
     // print("[DEBUG] rimeUpdate")
     rimeConsumeCommittedText()
@@ -420,6 +424,7 @@ private extension SquirrelInputController {
     var status = RimeStatus_stdbool.rimeStructInit()
     if rimeAPI.get_status(session, &status) {
       // enable schema specific ui style
+      // swiftlint:disable:next identifier_name
       if let schema_id = status.schema_id, schemaId == "" || schemaId != String(cString: schema_id) {
         schemaId = String(cString: schema_id)
         NSApp.squirrelAppDelegate.loadSettings(for: schemaId)
@@ -484,15 +489,20 @@ private extension SquirrelInputController {
         comments.append(candidate.comment.map { String(cString: $0) } ?? "")
       }
       var labels = [String]()
+      // swiftlint:disable identifier_name
       if let select_keys = ctx.menu.select_keys {
-        labels = Array(arrayLiteral: String(cString: select_keys))
+        labels = String(cString: select_keys).map { String($0) }
       } else if let select_labels = ctx.select_labels {
         let pageSize = Int(ctx.menu.page_size)
         for i in 0..<pageSize {
           labels.append(select_labels[i].map { String(cString: $0) } ?? "")
         }
       }
-      showPanel(preedit: inlinePreedit ? "" : preedit, selRange: NSRange(location: start.utf16Offset(in: preedit), length: preedit.utf16.distance(from: start, to: end)), caretPos: caretPos.utf16Offset(in: preedit), candidates: candidates, comments: comments, labels: labels, highlighted: Int(ctx.menu.highlighted_candidate_index))
+      // swiftlint:enable identifier_name
+
+      let selRange = NSRange(location: start.utf16Offset(in: preedit), length: preedit.utf16.distance(from: start, to: end))
+      showPanel(preedit: inlinePreedit ? "" : preedit, selRange: selRange, caretPos: caretPos.utf16Offset(in: preedit),
+                candidates: candidates, comments: comments, labels: labels, highlighted: Int(ctx.menu.highlighted_candidate_index))
       _ = rimeAPI.free_context(&ctx)
     } else {
       hidePalettes()
@@ -531,6 +541,7 @@ private extension SquirrelInputController {
     client.setMarkedText(attrString, selectionRange: NSRange(location: caretPos, length: 0), replacementRange: NSRange(location: NSNotFound, length: 0))
   }
 
+  // swiftlint:disable:next function_parameter_count
   func showPanel(preedit: String, selRange: NSRange, caretPos: Int, candidates: [String], comments: [String], labels: [String], highlighted: Int) {
     // print("[DEBUG] showPanelWithPreedit:...:")
     guard let client = client else { return }
diff --git a/sources/SquirrelPanel.swift b/sources/SquirrelPanel.swift
index da6d32fab..52a00d0d2 100644
--- a/sources/SquirrelPanel.swift
+++ b/sources/SquirrelPanel.swift
@@ -64,6 +64,7 @@ final class SquirrelPanel: NSPanel {
     view.currentTheme.inlineCandidate
   }
 
+  // swiftlint:disable:next cyclomatic_complexity
   override func sendEvent(_ event: NSEvent) {
     switch event.type {
     case .leftMouseDown:
@@ -98,7 +99,7 @@ final class SquirrelPanel: NSPanel {
     case .scrollWheel:
       if event.phase == .began {
         scrollDirection = .zero
-      // Scrollboard span
+        // Scrollboard span
       } else if event.phase == .ended || (event.phase == .init(rawValue: 0) && event.momentumPhase != .init(rawValue: 0)) {
         if abs(scrollDirection.dx) > abs(scrollDirection.dy) && abs(scrollDirection.dx) > 10 {
           _ = inputController?.page(up: (scrollDirection.dx < 0) == vertical)
@@ -106,7 +107,7 @@ final class SquirrelPanel: NSPanel {
           _ = inputController?.page(up: scrollDirection.dx > 0)
         }
         scrollDirection = .zero
-      // Mouse scroll wheel
+        // Mouse scroll wheel
       } else if event.phase == .init(rawValue: 0) && event.momentumPhase == .init(rawValue: 0) {
         if scrollTime.timeIntervalSinceNow < -1 {
           scrollDirection = .zero
@@ -139,6 +140,7 @@ final class SquirrelPanel: NSPanel {
   }
 
   // Main function to add attributes to text output from librime
+  // swiftlint:disable:next cyclomatic_complexity function_parameter_count
   func update(preedit: String, selRange: NSRange, caretPos: Int, candidates: [String], comments: [String], labels: [String], highlighted index: Int, update: Bool) {
     if update {
       self.preedit = preedit
@@ -335,6 +337,7 @@ private extension SquirrelPanel {
 
   // Get the window size, the windows will be the dirtyRect in
   // SquirrelView.drawRect
+  // swiftlint:disable:next cyclomatic_complexity
   func show() {
     currentScreen()
     let theme = view.currentTheme
@@ -437,7 +440,8 @@ private extension SquirrelPanel {
     text.addAttribute(.paragraphStyle, value: theme.paragraphStyle, range: NSRange(location: 0, length: text.length))
     view.textContentStorage.attributedString = text
     view.textView.setLayoutOrientation(vertical ? .vertical : .horizontal)
-    view.drawView(candidateRanges: [NSRange(location: 0, length: text.length)], hilightedIndex: -1, preeditRange: NSRange(location: NSNotFound, length: 0), highlightedPreeditRange: NSRange(location: NSNotFound, length: 0))
+    view.drawView(candidateRanges: [NSRange(location: 0, length: text.length)], hilightedIndex: -1,
+                  preeditRange: NSRange(location: NSNotFound, length: 0), highlightedPreeditRange: NSRange(location: NSNotFound, length: 0))
     show()
 
     statusTimer?.invalidate()
diff --git a/sources/SquirrelTheme.swift b/sources/SquirrelTheme.swift
index 035903c6b..232f4e581 100644
--- a/sources/SquirrelTheme.swift
+++ b/sources/SquirrelTheme.swift
@@ -294,12 +294,12 @@ private extension SquirrelTheme {
   func blendColor(foregroundColor: NSColor, backgroundColor: NSColor?) -> NSColor {
     let foregroundColor = foregroundColor.usingColorSpace(NSColorSpace.deviceRGB)!
     let backgroundColor = (backgroundColor ?? NSColor.gray).usingColorSpace(NSColorSpace.deviceRGB)!
-    func blend(_ a: CGFloat, _ b: CGFloat) -> CGFloat {
-      return (a * 2 + b) / 3
+    func blend(foreground: CGFloat, background: CGFloat) -> CGFloat {
+      return (foreground * 2 + background) / 3
     }
-    return NSColor(deviceRed: blend(foregroundColor.redComponent, backgroundColor.redComponent),
-                   green: blend(foregroundColor.greenComponent, backgroundColor.greenComponent),
-                   blue: blend(foregroundColor.blueComponent, backgroundColor.blueComponent),
-                   alpha: blend(foregroundColor.alphaComponent, backgroundColor.alphaComponent))
+    return NSColor(deviceRed: blend(foreground: foregroundColor.redComponent, background: backgroundColor.redComponent),
+                   green: blend(foreground: foregroundColor.greenComponent, background: backgroundColor.greenComponent),
+                   blue: blend(foreground: foregroundColor.blueComponent, background: backgroundColor.blueComponent),
+                   alpha: blend(foreground: foregroundColor.alphaComponent, background: backgroundColor.alphaComponent))
   }
 }
diff --git a/sources/SquirrelView.swift b/sources/SquirrelView.swift
index 89ab93b83..e364ee359 100644
--- a/sources/SquirrelView.swift
+++ b/sources/SquirrelView.swift
@@ -10,7 +10,8 @@ import AppKit
 private class SquirrelLayoutDelegate: NSObject, NSTextLayoutManagerDelegate {
   func textLayoutManager(_ textLayoutManager: NSTextLayoutManager, shouldBreakLineBefore location: any NSTextLocation, hyphenating: Bool) -> Bool {
     let index = textLayoutManager.offset(from: textLayoutManager.documentRange.location, to: location)
-    if let attributes = textLayoutManager.textContainer?.textView?.textContentStorage?.attributedString?.attributes(at: index, effectiveRange: nil), let noBreak = attributes[.noBreak] as? Bool, noBreak {
+    if let attributes = textLayoutManager.textContainer?.textView?.textContentStorage?.attributedString?.attributes(at: index, effectiveRange: nil),
+       let noBreak = attributes[.noBreak] as? Bool, noBreak {
       return false
     }
     return true
@@ -83,6 +84,7 @@ final class SquirrelView: NSView {
     if preeditRange.length > 0 {
       ranges.append(preeditRange)
     }
+    // swiftlint:disable:next identifier_name
     var x0 = CGFloat.infinity, x1 = -CGFloat.infinity, y0 = CGFloat.infinity, y1 = -CGFloat.infinity
     for range in ranges {
       if let textRange = convert(range: range) {
@@ -97,6 +99,7 @@ final class SquirrelView: NSView {
   }
   // Get the rectangle containing the range of text, will first convert to glyph range, expensive to calculate
   func contentRect(range: NSTextRange) -> NSRect {
+    // swiftlint:disable:next identifier_name
     var x0 = CGFloat.infinity, x1 = -CGFloat.infinity, y0 = CGFloat.infinity, y1 = -CGFloat.infinity
     textLayoutManager.enumerateTextSegments(in: range, type: .standard, options: .rangeNotRequired) { _, rect, _, _ in
       x0 = min(rect.minX, x0)
@@ -118,6 +121,7 @@ final class SquirrelView: NSView {
   }
 
   // All draws happen here
+  // swiftlint:disable:next cyclomatic_complexity
   override func draw(_ dirtyRect: NSRect) {
     var backgroundPath: CGPath?
     var preeditPath: CGPath?
@@ -158,7 +162,8 @@ final class SquirrelView: NSView {
       } else {
         // Draw other highlighted Rect
         if candidate.length > 0 && theme.candidateBackColor != nil {
-          let candidatePath = drawPath(highlightedRange: candidate, backgroundRect: backgroundRect, preeditRect: preeditRect, containingRect: containingRect, extraExpansion: theme.surroundingExtraExpansion)
+          let candidatePath = drawPath(highlightedRange: candidate, backgroundRect: backgroundRect, preeditRect: preeditRect,
+                                       containingRect: containingRect, extraExpansion: theme.surroundingExtraExpansion)
           if candidatePaths == nil {
             candidatePaths = CGMutablePath()
           }
@@ -413,6 +418,7 @@ private extension SquirrelView {
     } else if lineRects.count > 2 {
       leadingRect = lineRects[0]
       trailingRect = lineRects[lineRects.count-1]
+      // swiftlint:disable:next identifier_name
       var x0 = CGFloat.infinity, x1 = -CGFloat.infinity, y0 = CGFloat.infinity, y1 = -CGFloat.infinity
       for i in 1..<(lineRects.count-1) {
         let rect = lineRects[i]