diff --git a/.github/workflows/code-format.yml b/.github/workflows/code-format.yml
new file mode 100644
index 000000000..60980bae1
--- /dev/null
+++ b/.github/workflows/code-format.yml
@@ -0,0 +1,35 @@
+name: Check code formatting
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+
+jobs:
+  spotless:
+    name: Check Java formatting (Spotless)
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v5
+      - uses: actions/setup-java@v5
+        with:
+          java-version: 17
+          distribution: temurin
+      - uses: actions/cache@v4
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: |
+            ${{ runner.os }}-gradle-
+      - name: Validate Gradle Wrapper
+        uses: gradle/actions/wrapper-validation@v4
+      - name: Check formatting
+        run: ./gradlew spotlessCheck
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 49414fe1b..6d33e5aba 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -73,18 +73,15 @@ esp. before/after screenshots.
 
 ### Coding Conventions
 
-Source files are partly derived from different other open source projects
-and may follow different coding styles and conventions.
-
-If you do a PR fixing a bug or adding a feature,
-please embrace the coding convention you see in the corresponding files,
-so that the result fits well together.
-
-Do not refactor or rename things in the same PR
-to make the diff small and the PR easy to review.
-
 Project language is Java.
 
+Code formatting is enforced via [Spotless](https://github.com/diffplug/spotless) Gradle plugin.
+Auto-format all files by running `./gradlew spotlessApply` before opening a PR.
+CI will fail if files are not formatted correctly so make sure to run the formatter before pushing.
+
+If you do a PR fixing a bug or adding a feature, do not refactor or rename things in the same PR
+to make the diff small and the PR easy to review.
+
 By using [Delta Chat Core](https://github.com/deltachat/deltachat-core-rust)
 there is already a strong separation between "UI" and "Model".
 Further separations and abstraction layers are often not helpful
diff --git a/build.gradle b/build.gradle
index 66116c4e1..0e0d19854 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,6 +1,7 @@
 plugins {
     id 'com.android.application' version '8.11.1'
     id 'com.google.gms.google-services' version '4.4.1'
+    id 'com.diffplug.spotless' version '8.3.0'
 }
 
 repositories {
@@ -151,6 +152,31 @@ android {
 
 }
 
+spotless {
+    java {
+        target 'src/*/java/**/*.java'
+        targetExclude 'src/main/java/chat/delta/**' // ignore auto-generated code
+        googleJavaFormat()  // Google style = 2-space indent, matches Android Studio defaults
+        removeUnusedImports()
+        trimTrailingWhitespace()
+        endWithNewline()
+    }
+    format 'xml', {
+        target 'src/*/res/**/*.xml', 'src/*/AndroidManifest.xml'
+        eclipseWtp('xml')
+        leadingTabsToSpaces(2)
+        trimTrailingWhitespace()
+        endWithNewline()
+    }
+     groovy {
+        target '*.gradle'
+        greclipse()
+        leadingTabsToSpaces(2)
+        trimTrailingWhitespace()
+        endWithNewline()
+    }
+}
+
 dependencies {
     def media3_version = "1.8.0"   // 1.9.0 need minSdkVersion 23
 
diff --git a/settings.gradle b/settings.gradle
index 8aeca1ea1..492070dea 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -1,5 +1,6 @@
 pluginManagement {
     repositories {
+        gradlePluginPortal()
         google()
         mavenCentral()
     }