diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 00000000..28f32471
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,82 @@
+name: CI
+
+# Compiles the app and its test target on every pull request and push to main, so a PR that
+# doesn't build never reaches a reviewer. The build is for a generic iOS device with code
+# signing off: that proves the code compiles against the SDK without needing certificates,
+# and it matches how the app is actually run (on a phone; the simulator can't do Bluetooth
+# or on-device MLX).
+#
+# Standard GitHub-hosted macOS runners are free for public repositories. Keep this on the
+# plain `macos-*` labels — "larger" runners are billed even for public repos.
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+concurrency:
+  group: ci-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+env:
+  # Pin the Xcode on the image so a runner image update can't change the SDK underneath a PR.
+  # Bump deliberately (and check the pinned mlx-swift-lm still compiles) when moving to a new
+  # Xcode. Xcode 27 is not on GitHub's images yet; see actions/runner-images.
+  DEVELOPER_DIR: /Applications/Xcode_26.6.app/Contents/Developer
+
+jobs:
+  build:
+    name: Build app + tests (iOS device, unsigned)
+    runs-on: macos-26
+    timeout-minutes: 90
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Provide the gitignored config files
+        # Same two copies the README asks a new contributor to make. The project refuses to
+        # build without them; the examples' placeholder values are enough to compile, and the
+        # real values only matter at runtime on a device.
+        run: |
+          cp Config.xcconfig.example Config.xcconfig
+          cp OpenVision/Config/Config.swift.example OpenVision/Config/Config.swift
+
+      - name: Cache Swift packages
+        # Package.resolved is gitignored (whole xcworkspace), so key on the files that hold
+        # the pins. The MLX, Kokoro and Meta DAT checkouts are the slow part of a cold build.
+        uses: actions/cache@v4
+        with:
+          path: .spm
+          key: spm-${{ runner.os }}-${{ hashFiles('OpenVision.xcodeproj/project.pbxproj', 'project.yml') }}
+          restore-keys: spm-${{ runner.os }}-
+
+      - name: Show toolchain
+        run: |
+          xcodebuild -version
+          xcrun --sdk iphoneos --show-sdk-version
+
+      - name: Build for testing
+        # mlx-swift ships a build plugin (CudaBuild) and mlx-swift-lm uses Swift macros; Xcode
+        # refuses both until a human approves them, which is what the two -skip flags do here.
+        run: |
+          set -o pipefail
+          xcodebuild build-for-testing \
+            -project OpenVision.xcodeproj \
+            -scheme OpenVision \
+            -destination 'generic/platform=iOS' \
+            -clonedSourcePackagesDirPath .spm \
+            -derivedDataPath DerivedData \
+            -skipPackagePluginValidation \
+            -skipMacroValidation \
+            CODE_SIGNING_ALLOWED=NO \
+            CODE_SIGNING_REQUIRED=NO \
+            CODE_SIGN_IDENTITY= \
+            DEVELOPMENT_TEAM= \
+          | xcbeautify --renderer github-actions
+
+      - name: Upload build log on failure
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: xcodebuild-logs
+          path: DerivedData/Logs/Build/*.xcactivitylog
+          if-no-files-found: ignore
diff --git a/README.md b/README.md
index 9a05dc73..fbd56f7a 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,7 @@
 [![Swift 5](https://img.shields.io/badge/Swift-5-orange.svg)](https://swift.org)
 [![iOS 18+](https://img.shields.io/badge/iOS-18+-blue.svg)](https://developer.apple.com/ios/)
 [![Latest release](https://img.shields.io/github/v/release/rayl15/OpenVision?color=2ea44f)](https://github.com/rayl15/OpenVision/releases)
+[![CI](https://github.com/rayl15/OpenVision/actions/workflows/ci.yml/badge.svg)](https://github.com/rayl15/OpenVision/actions/workflows/ci.yml)
 [![Stars](https://img.shields.io/github/stars/rayl15/OpenVision?logo=github)](https://github.com/rayl15/OpenVision/stargazers)
 [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg)](https://github.com/rayl15/OpenVision/blob/main/CONTRIBUTING.md)
 [![good first issues](https://img.shields.io/github/issues/rayl15/OpenVision/good%20first%20issue?color=7057ff&label=good%20first%20issues)](https://github.com/rayl15/OpenVision/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22)