diff --git a/.github/actions/java-test/action.yaml b/.github/actions/java-test/action.yaml
index f82f05b23..e1efd9fce 100644
--- a/.github/actions/java-test/action.yaml
+++ b/.github/actions/java-test/action.yaml
@@ -49,7 +49,7 @@ runs:
     - name: Run Maven compile
       shell: bash
       run: |
-        ./mvnw -B compile test-compile scalafix:scalafix -Psemanticdb ${{ inputs.maven_opts }}
+        ./mvnw -B compile test-compile scalafix:scalafix -Dscalafix.mode=CHECK -Psemanticdb ${{ inputs.maven_opts }}
 
     - name: Run tests
       shell: bash
diff --git a/DEVELOPMENT.md b/DEVELOPMENT.md
index 25a65999e..6dc0f1f23 100644
--- a/DEVELOPMENT.md
+++ b/DEVELOPMENT.md
@@ -84,3 +84,7 @@ in the respective source code, e.g., `CometTPCHQueryBenchmark`.
 ## Debugging
 Comet is a multi-language project with native code written in Rust and JVM code written in Java and Scala.
 It is possible to debug both native and JVM code concurrently as described in the [DEBUGGING guide](DEBUGGING.md)
+
+## Submitting a Pull Request
+Comet uses `cargo fmt`, [Scalafix](https://github.com/scalacenter/scalafix) and [Spotless](https://github.com/diffplug/spotless/tree/main/plugin-maven) to 
+automatically format the code. Before submitting a pull request, you can simply run `make format` to format the code.
\ No newline at end of file
diff --git a/Makefile b/Makefile
index 6f599a081..ca5d7564a 100644
--- a/Makefile
+++ b/Makefile
@@ -38,6 +38,7 @@ clean:
 bench:
 	cd core && RUSTFLAGS="-Ctarget-cpu=native" cargo bench $(filter-out $@,$(MAKECMDGOALS))
 format:
+	cd core && cargo fmt
 	./mvnw compile test-compile scalafix:scalafix -Psemanticdb $(PROFILES)
 	./mvnw spotless:apply $(PROFILES)
 
diff --git a/spark/src/main/scala/org/apache/comet/CometSparkSessionExtensions.scala b/spark/src/main/scala/org/apache/comet/CometSparkSessionExtensions.scala
index 87c2265fc..5720b6935 100644
--- a/spark/src/main/scala/org/apache/comet/CometSparkSessionExtensions.scala
+++ b/spark/src/main/scala/org/apache/comet/CometSparkSessionExtensions.scala
@@ -26,7 +26,6 @@ import org.apache.spark.internal.Logging
 import org.apache.spark.network.util.ByteUnit
 import org.apache.spark.sql.SparkSession
 import org.apache.spark.sql.SparkSessionExtensions
-import org.apache.spark.sql.catalyst.expressions.AttributeReference
 import org.apache.spark.sql.catalyst.rules.Rule
 import org.apache.spark.sql.comet._
 import org.apache.spark.sql.comet.execution.shuffle.{CometColumnarShuffle, CometNativeShuffle}
diff --git a/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala b/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala
index 08a499b06..902f7037f 100644
--- a/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala
@@ -28,7 +28,7 @@ import org.apache.spark.sql.catalyst.expressions.objects.StaticInvoke
 import org.apache.spark.sql.catalyst.optimizer.NormalizeNaNAndZero
 import org.apache.spark.sql.catalyst.plans.physical.{HashPartitioning, Partitioning, SinglePartition}
 import org.apache.spark.sql.catalyst.util.CharVarcharCodegenUtils
-import org.apache.spark.sql.comet.{CometHashAggregateExec, CometPlan, CometSinkPlaceHolder, DecimalPrecision}
+import org.apache.spark.sql.comet.{CometSinkPlaceHolder, DecimalPrecision}
 import org.apache.spark.sql.execution
 import org.apache.spark.sql.execution._
 import org.apache.spark.sql.execution.aggregate.HashAggregateExec
diff --git a/spark/src/test/scala/org/apache/comet/CometCastSuite.scala b/spark/src/test/scala/org/apache/comet/CometCastSuite.scala
index 565d2264b..317371fb9 100644
--- a/spark/src/test/scala/org/apache/comet/CometCastSuite.scala
+++ b/spark/src/test/scala/org/apache/comet/CometCastSuite.scala
@@ -90,13 +90,13 @@ class CometCastSuite extends CometTestBase with AdaptiveSparkPlanHelper {
     Range(0, len).map(_ => chars.charAt(r.nextInt(chars.length))).mkString
   }
 
-  private def fuzzCastFromString(chars: String, maxLen: Int, toType: DataType) {
+  private def fuzzCastFromString(chars: String, maxLen: Int, toType: DataType): Unit = {
     val r = new Random(0)
     val inputs = Range(0, 10000).map(_ => genString(r, chars, maxLen))
     castTest(inputs.toDF("a"), toType)
   }
 
-  private def castTest(input: DataFrame, toType: DataType) {
+  private def castTest(input: DataFrame, toType: DataType): Unit = {
     withTempPath { dir =>
       val df = roundtripParquet(input, dir)
         .withColumn("converted", col("a").cast(toType))
diff --git a/spark/src/test/scala/org/apache/comet/CometExpressionSuite.scala b/spark/src/test/scala/org/apache/comet/CometExpressionSuite.scala
index 7424f1bfd..803f30bed 100644
--- a/spark/src/test/scala/org/apache/comet/CometExpressionSuite.scala
+++ b/spark/src/test/scala/org/apache/comet/CometExpressionSuite.scala
@@ -24,7 +24,7 @@ import java.util
 import org.apache.hadoop.fs.Path
 import org.apache.spark.sql.{CometTestBase, DataFrame, Row}
 import org.apache.spark.sql.execution.adaptive.AdaptiveSparkPlanHelper
-import org.apache.spark.sql.functions.{expr, lit}
+import org.apache.spark.sql.functions.expr
 import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.internal.SQLConf.SESSION_LOCAL_TIMEZONE
 import org.apache.spark.sql.types.{Decimal, DecimalType, StructType}