diff --git a/.github/regenerate-good.sh b/.github/regenerate-good.sh
new file mode 100755
index 0000000..943ed0b
--- /dev/null
+++ b/.github/regenerate-good.sh
@@ -0,0 +1,14 @@
+#!/bin/sh
+act -W .github/workflows/test-regenerate-good.yml 2>/dev/null |
+perl -ne '
+    unless ($state) {
+        $state = 1 if (/run-scalafmt\.sh/);
+        next;
+    }
+    if ($state == 1) {
+        $state = 2 if (/docker exec/);
+        next;
+    }
+    last unless s/^.*\| //;
+    print;
+' > .github/testdata/Good.scala
diff --git a/.github/testdata/.scalafmt.conf b/.github/testdata/.scalafmt.conf
index ae8e9a8..f7da8a3 100644
--- a/.github/testdata/.scalafmt.conf
+++ b/.github/testdata/.scalafmt.conf
@@ -1,3 +1,5 @@
-# I dont like this formatting directive in reality, but lets
+# I don't like this formatting directive in reality, but it lets
 # us verify that this is reading a conf file easily
-align = most
+align.preset = most
+version = 3.7.15
+runner.dialect = scala213
diff --git a/.github/testdata/Bad.scala b/.github/testdata/Bad.scala
index f65f5d7..85b0fa8 100644
--- a/.github/testdata/Bad.scala
+++ b/.github/testdata/Bad.scala
@@ -16,7 +16,6 @@ sealed abstract class Formatted {
 }
 
 /** Aligned by first asterisk, default ScalaDoc style is second.
- *
  */
 object Formatted {
     case class Success(formattedCode: String) extends Formatted
diff --git a/.github/testdata/Good.scala b/.github/testdata/Good.scala
index 264d1ae..7dad55e 100644
--- a/.github/testdata/Good.scala
+++ b/.github/testdata/Good.scala
@@ -3,6 +3,7 @@ messiness added to it. -mroth */
 package org.scalafmt
 
 sealed abstract class Formatted {
+
   def toEither: Either[Throwable, String] = this match {
     case Formatted.Success(s) => Right(s)
     case Formatted.Failure(e) => Left(e) // too much space before comment
@@ -15,7 +16,6 @@ sealed abstract class Formatted {
 }
 
 /** Aligned by first asterisk, default ScalaDoc style is second.
-  *
   */
 object Formatted {
   case class Success(formattedCode: String) extends Formatted
diff --git a/.github/workflows/test-all.yml b/.github/workflows/test-all.yml
new file mode 100644
index 0000000..2d168ad
--- /dev/null
+++ b/.github/workflows/test-all.yml
@@ -0,0 +1,12 @@
+on: [workflow_dispatch]
+name: Check with all testdata
+
+jobs:
+  check-testdata:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Checking testdata
+        uses: ./
+        with:
+          args: "-c .github/testdata/.scalafmt.conf --list"
diff --git a/.github/workflows/test-regenerate-good.yml b/.github/workflows/test-regenerate-good.yml
new file mode 100644
index 0000000..d089d7d
--- /dev/null
+++ b/.github/workflows/test-regenerate-good.yml
@@ -0,0 +1,12 @@
+on: [workflow_dispatch]
+name: Regenerate Good file (run in act)
+
+jobs:
+  regenerate-good:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Checking testdata
+        uses: ./
+        with:
+          args: "-c .github/testdata/.scalafmt.conf --stdout .github/testdata/Bad.scala"
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 17908a5..1010c85 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -1,12 +1,12 @@
 on: [push]
-name: Check with testdata
+name: Check with good testdata
 
 jobs:
-  check-testdata:
+  check-good-testdata:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
-      - name: Checking testdata
+      - uses: actions/checkout@v4
+      - name: Checking testdata (pass)
         uses: ./
         with:
           args: "-c .github/testdata/.scalafmt.conf --exclude .github/testdata/Bad.scala --list"
diff --git a/Dockerfile b/Dockerfile
deleted file mode 100644
index 09b53be..0000000
--- a/Dockerfile
+++ /dev/null
@@ -1,10 +0,0 @@
-# This is essentially just scalafmt loaded into an alpine container, so
-# that we have a shell present to expand wildcards etc.
-FROM mrothy/scalafmt:2.3.2 as scalafmt
-
-FROM eclipse-temurin:11-jre
-
-COPY --from=scalafmt /usr/local/bin/scalafmt /usr/local/bin/scalafmt
-COPY entrypoint.sh /entrypoint.sh
-ENTRYPOINT ["/entrypoint.sh"]
-CMD ["--list"]
diff --git a/Makefile b/Makefile
index 4bc3353..7b921c8 100644
--- a/Makefile
+++ b/Makefile
@@ -1,34 +1,17 @@
-IMAGE := openlaw/scalafmt-ci
-# DEFAULT_ARGS := --list
-WORKDIR := /github/workspace
 TESTDATA := .github/testdata
 
 .PHONY: test testfail testdata clean
 
-image:
-	docker build -t $(IMAGE) .
-
 test:
-	docker run --rm -it \
-		-w=$(WORKDIR) \
-		-v "$$(pwd)/$(TESTDATA)":$(WORKDIR) \
-		$(IMAGE) --list --exclude Bad.scala
+	act -W .github/workflows/test.yml
 
 # expected failure, to see output
 testfail: 
-	docker run --rm -it \
-		-w=$(WORKDIR) \
-		-v "$$(pwd)/$(TESTDATA)":$(WORKDIR) \
-		$(IMAGE) --list
+	act -W .github/workflows/test-all.yml
 
 # generate the "good" version of the sample file
 $(TESTDATA)/Good.scala: $(TESTDATA)/Bad.scala $(TESTDATA)/.scalafmt.conf
-	docker run --rm -i \
-		-v "$$(pwd)/$(TESTDATA)":/conf \
-		mrothy/scalafmt-native:2.2.2 \
-			--config /conf/.scalafmt.conf \
-			--stdin --stdout \
-	< $< > $@
+	./.github/regenerate-good.sh
 
 testdata: $(TESTDATA)/Good.scala
 
diff --git a/README.md b/README.md
index 7a2e76f..277f909 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,8 @@
 # Scalafmt GitHub Action
 
-Runs `scalafmt --list` on your repository automatically with every push.
+Run `scalafmt` on your repository automatically with every push.
+
+By default, it runs with `--list`, but that's configurable.
 
 Uses [scalafmt-native](https://github.com/mroth/scalafmt-native) under the hood
 to keep things small and booting super quick by avoiding the JVM. :racehorse:
@@ -11,7 +13,7 @@ Simply add a step such as the following to your your workflow yml file:
 
 ```yml
 - name: Check for scalafmt conformance
-  uses: openlawteam/scalafmt-ci@v2
+  uses: garnercorp/scalafmt-ci@v3
 ```
 
 Example in the full context of a workflow file, with some optional arguments:
@@ -24,28 +26,19 @@ jobs:
   scalafmt-lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 1
       - name: Checking your code to see if u r naughty or nice
-        uses: openlawteam/scalafmt-ci@v2
+        uses: garnercorp/scalafmt-ci@v3
         with:
           args: "--exclude=third_party --list"
 ```
 
-### Installing with GitHub Marketplace
-
-https://github.com/marketplace/actions/scalafmt-action
+## Compatibility
 
-### (Legacy) HCL Syntax
+### v2 to v3
 
-If you are still using legacy HCL format (from the GitHub Actions Alpha test),
-you will need to pin to a previous version of this action.
-
-```hcl
-action "lint" {
-  uses="openlawteam/scalafmt-ci@v0"
-  # optional additional args
-  args="--exclude ./vendor"
-}
-```
+- [v2](https://github.com/garnerCorp/scalafmt-ci/tree/v2) is built around [scalafmt](https://github.com/scalameta/scalafmt) [`3.5.2`](https://github.com/scalameta/scalafmt/releases/tag/v3.5.2), [v3](https://github.com/garnerCorp/scalafmt-ci/tree/v3) is built around scalafmt [`3.7+`](https://github.com/scalameta/scalafmt/releases/tag/v3.7.15)
+  - The formatting defaults have changed
+  - `--list --test` is no longer accepted as arguments, you should try just one of them.
diff --git a/action.yml b/action.yml
index a183910..4def6f9 100644
--- a/action.yml
+++ b/action.yml
@@ -1,6 +1,6 @@
 name: "Scalafmt Action"
 description: "Format Scala code using scalafmt"
-author: "Matthew Rothenberg <mroth@openlaw.io>"
+author: "GarnerCorp <opensource@garnercorp.com>"
 branding:
   icon: "wind"
   color: "red"
@@ -9,8 +9,40 @@ inputs:
     description: "Args to pass to scalafmt"
     default: "--list"
     required: false
+  version:
+    description: "Version of scalafmt"
+    default: "3.7.15"
+    required: false
+
 runs:
-  using: "docker"
-  image: "Dockerfile"
-  args:
-    - ${{ inputs.args }}
+  using: "composite"
+  steps:
+  - shell: bash
+    run: |
+      "$action_path/set-path.sh"
+    env:
+      scalafmt_version: ${{ inputs.version }}
+      action_path: ${{ github.action_path }}
+  - uses: actions/cache/restore@v4
+    id: cache
+    with:
+      path: ${{ env.SCALAFMT_PATH }}
+      key: scalafmt-${{ inputs.version }}
+  - shell: bash
+    id: retrieve-scalafmt
+    if: ${{ !steps.cache.outputs.cache-hit }}
+    run: |
+      curl -sL https://github.com/scalameta/scalafmt/releases/download/v${scalafmt_version}/scalafmt-linux-glibc > "$SCALAFMT_PATH/scalafmt"
+      chmod +x "$SCALAFMT_PATH/scalafmt"
+      echo "retrieved=1" >> "$GITHUB_OUTPUT"
+  - shell: bash
+    run: |
+      run-scalafmt.sh
+    env:
+      args: ${{ inputs.args }}
+  - name: Cache scalafmt
+    if: ${{ always() && steps.retrieve-scalafmt.outputs.retrieved }}
+    uses: actions/cache/save@v4
+    with:
+      path: ${{ env.SCALAFMT_PATH }}
+      key: scalafmt-${{ inputs.version }}
diff --git a/entrypoint.sh b/entrypoint.sh
deleted file mode 100755
index 1d0389b..0000000
--- a/entrypoint.sh
+++ /dev/null
@@ -1,2 +0,0 @@
-#!/bin/sh
-sh -c "/usr/local/bin/scalafmt --non-interactive $*"
diff --git a/extract-errors.pl b/extract-errors.pl
new file mode 100755
index 0000000..091d8b9
--- /dev/null
+++ b/extract-errors.pl
@@ -0,0 +1,22 @@
+#!/usr/bin/env perl
+my $source_file = $ENV{source};
+my $errors_file = $ENV{errors};
+my $new_source_file = "$source_file.new";
+open my $source_in, "<", $source_file;
+open my $source_out, ">", $new_source_file;
+open my $errors, ">>", $errors_file;
+my $found_error=0;
+while (<$source_in>) {
+  if ($found_error) {
+    print $errors $_;
+  } elsif (/^error:|^Segmentation fault/) {
+    $found_error=1;
+    print $errors $_;
+  } else {
+    print $source_out $_;
+  }
+}
+close $source_in;
+close $source_out;
+close $errors;
+rename $new_source_file, $source_file;
diff --git a/run-scalafmt.sh b/run-scalafmt.sh
new file mode 100755
index 0000000..6f538b1
--- /dev/null
+++ b/run-scalafmt.sh
@@ -0,0 +1,45 @@
+#!/bin/sh
+output=$(mktemp)
+warnings=$(mktemp)
+errors=$(mktemp)
+
+enforce_scala_format_version() {
+  if [ -e .scalafmt.conf ]; then
+    perl -pi -e 'next unless s/^\s*(version)=.*/$1=$ENV{scalafmt_version}/' .scalafmt.conf
+  fi
+}
+
+enforce_scala_format_version
+scalafmt --non-interactive $args > "$output" 2> "$warnings"
+result=$?
+cat "$output"
+cat "$warnings" >&2
+[ $result -eq 0 ] && exit
+
+report() {
+    file="$1"
+    summary="$2"
+
+    [ -s "$file" ] || return
+    echo "<details><summary>$summary</summary>"
+    echo
+    echo '```'
+    perl -pe 's/$ENV{GITHUB_WORKSPACE}//g' "$file"
+    echo '```'
+    echo '</details>'
+    echo
+}
+
+source="$output" errors="$errors" extract-errors.pl
+source="$warnings" errors="$errors" extract-errors.pl
+
+(
+    echo "# scalafmt failed ($result)"
+    if [ -s "$errors" ]; then
+      echo '# Errors'
+      cat "$errors"
+    fi
+    report "$warnings" "Warnings"
+    report "$output" "Status"
+) >> "$GITHUB_STEP_SUMMARY"
+exit $result
diff --git a/set-path.sh b/set-path.sh
new file mode 100755
index 0000000..e91d1cd
--- /dev/null
+++ b/set-path.sh
@@ -0,0 +1,11 @@
+#!/bin/sh
+SCALAFMT_PATH="/tmp/scalafmt/${scalafmt_version}"
+mkdir -p "$SCALAFMT_PATH"
+(
+    echo "SCALAFMT_PATH=$SCALAFMT_PATH"
+    echo "scalafmt_version=$scalafmt_version"
+) >> "$GITHUB_ENV"
+(
+    echo "$SCALAFMT_PATH"
+    echo "$action_path"
+) >> "$GITHUB_PATH"