diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f479903..b624a50 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -16,7 +16,12 @@ jobs:
           distribution: temurin
           java-version: 17
       - uses: sbt/setup-sbt@8feba82adc7f01ddcf8165b86f778bdb5b82cebc # v1
-      - run: sbt compile
+      # scalafmt は非コンパイルで最速に落ち、scalafix は semanticdb 付きの
+      # コンパイルを伴うため、その後の compile は追加コストがほぼない。
+      # sbtn (thin client) は argv を 1 本の文字列に連結するため引数付きの
+      # タスクをクォートで区切れない。`;` 区切りの単一コマンドとして渡す。
+      - name: Lint and compile
+        run: sbt "scalafmtCheckAll; scalafmtSbtCheck; scalafixAll --check; compile"
 
   build-linux:
     if: github.event_name == 'push' || github.event_name == 'pull_request'
diff --git a/.scalafix.conf b/.scalafix.conf
new file mode 100644
index 0000000..c033c70
--- /dev/null
+++ b/.scalafix.conf
@@ -0,0 +1,13 @@
+rules = [
+  OrganizeImports
+  RemoveUnused
+  RedundantSyntax
+  DisableSyntax
+]
+
+# unused import の削除は RemoveUnused に任せて二重適用を避ける
+OrganizeImports.removeUnused = false
+OrganizeImports.targetDialect = Scala3
+
+DisableSyntax.noFinalize = true
+DisableSyntax.noReturns = true
diff --git a/.scalafmt.conf b/.scalafmt.conf
index 08f6ef6..fe23d4c 100644
--- a/.scalafmt.conf
+++ b/.scalafmt.conf
@@ -4,3 +4,10 @@ runner.dialect = scala3
 runner.dialectOverride.allowSignificantIndentation = false
 # allows `if x then y`
 runner.dialectOverride.allowQuietSyntax = true
+
+# build.sbt / plugins.sbt の縦揃えを維持する。val の = は揃えない
+align.tokens."+" = [
+  { code = ":=" }
+  { code = "%" }
+  { code = "%%" }
+]
diff --git a/build.sbt b/build.sbt
index de8b31b..dea297e 100644
--- a/build.sbt
+++ b/build.sbt
@@ -2,10 +2,13 @@ import scala.scalanative.build.*
 
 enablePlugins(ScalaNativePlugin)
 
+ThisBuild / semanticdbEnabled := true
+ThisBuild / scalafmtOnCompile := true
+
 name         := "comport"
 organization := "dev.capslock"
 scalaVersion := "3.8.2"
-scalacOptions += "-no-indent"
+scalacOptions ++= Seq("-no-indent", "-Wunused:all")
 
 libraryDependencies ++= Seq(
   "com.lihaoyi"   %% "mainargs"   % "0.7.8",
diff --git a/project/plugins.sbt b/project/plugins.sbt
index a4fc4a7..9a4cc4d 100644
--- a/project/plugins.sbt
+++ b/project/plugins.sbt
@@ -1 +1,3 @@
 addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.5.12")
+addSbtPlugin("org.scalameta"    % "sbt-scalafmt"     % "2.6.2")
+addSbtPlugin("ch.epfl.scala"    % "sbt-scalafix"     % "0.14.7")