Index: clangd/ClangdServer.h
===================================================================
--- clangd/ClangdServer.h
+++ clangd/ClangdServer.h
@@ -23,6 +23,7 @@
 #include "index/FileIndex.h"
 #include "index/Index.h"
 #include "refactor/Tweak.h"
+#include "clang/Format/Format.h"
 #include "clang/Tooling/CompilationDatabase.h"
 #include "clang/Tooling/Core/Replacement.h"
 #include "llvm/ADT/FunctionExtras.h"
Index: clangd/ClangdServer.cpp
===================================================================
--- clangd/ClangdServer.cpp
+++ clangd/ClangdServer.cpp
@@ -10,6 +10,7 @@
 #include "ClangdUnit.h"
 #include "CodeComplete.h"
 #include "FindSymbols.h"
+#include "Format.h"
 #include "Headers.h"
 #include "SourceCode.h"
 #include "Trace.h"
@@ -362,8 +363,9 @@
 
 void ClangdServer::applyTweak(PathRef File, Range Sel, StringRef TweakID,
                               Callback<tooling::Replacements> CB) {
-  auto Action = [Sel](decltype(CB) CB, std::string File, std::string TweakID,
-                      Expected<InputsAndAST> InpAST) {
+  auto Action = [Sel, this](decltype(CB) CB, std::string File,
+                            std::string TweakID,
+                            Expected<InputsAndAST> InpAST) {
     if (!InpAST)
       return CB(InpAST.takeError());
     auto Selection = tweakSelection(Sel, *InpAST);
@@ -372,8 +374,15 @@
     auto A = prepareTweak(TweakID, *Selection);
     if (!A)
       return CB(A.takeError());
-    // FIXME: run formatter on top of resulting replacements.
-    return CB((*A)->apply(*Selection));
+    auto ResultReplacements = (*A)->apply(*Selection);
+    if (!ResultReplacements)
+      return CB(ResultReplacements.takeError());
+    // FIXME: this function has I/O operations (find .clang-format file), figure
+    // out a way to cache the format style.
+    auto Style = getFormatStyleForFile(File, InpAST->Inputs.Contents,
+                                       FSProvider.getFileSystem().get());
+    return CB(
+        cleanupAndFormat(InpAST->Inputs.Contents, *ResultReplacements, Style));
   };
   WorkScheduler.runWithAST(
       "ApplyTweak", File,
Index: clangd/Format.h
===================================================================
--- /dev/null
+++ clangd/Format.h
@@ -0,0 +1,28 @@
+//===--- Format.h ------------------------------------------------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Format/Format.h"
+#include "clang/Tooling/Core/Replacement.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Error.h"
+
+namespace clang {
+namespace clangd {
+
+// Cleanup and format the given replacements.
+inline llvm::Expected<tooling::Replacements>
+cleanupAndFormat(StringRef Code, const tooling::Replacements &Replaces,
+                 const format::FormatStyle &Style) {
+  auto CleanReplaces = cleanupAroundReplacements(Code, Replaces, Style);
+  if (!CleanReplaces)
+    return CleanReplaces;
+  return formatReplacements(Code, std::move(*CleanReplaces), Style);
+}
+
+} // namespace clangd
+} // namespace clang
Index: unittests/clangd/TweakTests.cpp
===================================================================
--- unittests/clangd/TweakTests.cpp
+++ unittests/clangd/TweakTests.cpp
@@ -9,6 +9,7 @@
 
 #include "Annotations.h"
 #include "SourceCode.h"
+#include "Format.h"
 #include "TestTU.h"
 #include "refactor/Tweak.h"
 #include "clang/AST/Expr.h"
@@ -77,7 +78,8 @@
 void checkNotAvailable(StringRef ID, llvm::StringRef Input) {
   return checkAvailable(ID, Input, /*Available=*/false);
 }
-llvm::Expected<std::string> apply(StringRef ID, llvm::StringRef Input) {
+llvm::Expected<std::string> apply(StringRef ID, llvm::StringRef Input,
+                                  bool Format) {
   Annotations Code(Input);
   Range SelectionRng;
   if (Code.points().size() != 0) {
@@ -102,12 +104,19 @@
   auto Replacements = (*T)->apply(S);
   if (!Replacements)
     return Replacements.takeError();
+  if (Format) {
+    Replacements = cleanupAndFormat(
+        Code.code(), *Replacements,
+        clang::format::getLLVMStyle());
+    if (!Replacements)
+      return Replacements.takeError();
+  }
   return applyAllReplacements(Code.code(), *Replacements);
 }
 
 void checkTransform(llvm::StringRef ID, llvm::StringRef Input,
-                    llvm::StringRef Output) {
-  EXPECT_THAT_EXPECTED(apply(ID, Input), HasValue(Output))
+                    llvm::StringRef Output, bool Format = false) {
+  EXPECT_THAT_EXPECTED(apply(ID, Input, Format), HasValue(Output))
       << "action id is" << ID;
 }
 
@@ -150,6 +159,22 @@
   )cpp";
   checkTransform(ID, Input, Output);
 
+  Input = R"cpp(
+    void test() {
+      ^if () { return 100; } else { continue; }
+    }
+  )cpp";
+  Output = R"cpp(
+    void test() {
+      if () {
+        continue;
+      } else {
+        return 100;
+      }
+    }
+  )cpp";
+  checkTransform(ID, Input, Output, /*Format=*/true);
+
   // Available in subexpressions of the condition.
   checkAvailable(ID, R"cpp(
     void test() {