diff --git a/.github/workflows/ahk-format.yml b/.github/workflows/ahk-format.yml
new file mode 100644
index 00000000..0a865827
--- /dev/null
+++ b/.github/workflows/ahk-format.yml
@@ -0,0 +1,48 @@
+name: AHK format
+
+on:
+  pull_request:
+    paths:
+      - "**.ahk"
+      - "Helper/Format-Ahk.ps1"
+      - "Helper/ahkfmt-exclude.list"
+      - "Helper/ahkfmt-tests/**"
+      - ".github/workflows/ahk-format.yml"
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  format:
+    name: Check AHK formatting
+    runs-on: windows-latest
+
+    steps:
+      - name: Check out pull request
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Run formatter tests
+        shell: powershell
+        run: ./Helper/Format-Ahk.ps1 -Test
+
+      - name: Check changed AHK files
+        shell: powershell
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+        run: |
+          # A changed formatter or exclude list can affect every file, so check them all.
+          $toolChanged = git diff --name-only "$env:BASE_SHA...HEAD" -- Helper/Format-Ahk.ps1 Helper/ahkfmt-exclude.list
+          if ($toolChanged) {
+            Write-Host 'Formatter changed: checking all tracked .ahk files.'
+            ./Helper/Format-Ahk.ps1 -Check
+          }
+          else {
+            ./Helper/Format-Ahk.ps1 -Check -Base $env:BASE_SHA
+          }
+          exit $LASTEXITCODE
diff --git a/.github/workflows/rust-helpers.yml b/.github/workflows/rust-helpers.yml
new file mode 100644
index 00000000..e2e973f2
--- /dev/null
+++ b/.github/workflows/rust-helpers.yml
@@ -0,0 +1,51 @@
+name: Rust helpers
+
+on:
+  pull_request:
+    paths:
+      - "Helper/carddb_src/**"
+      - "Helper/cardimage_src/**"
+      - ".github/workflows/rust-helpers.yml"
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    name: Build ${{ matrix.crate }}
+    runs-on: windows-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        crate: [carddb, cardimage]
+    env:
+      CARGO_TARGET_DIR: ${{ github.workspace }}/target
+
+    steps:
+      - name: Check out pull request
+        uses: actions/checkout@v6
+
+      - name: Install Rust stable
+        id: toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: x86_64-pc-windows-msvc
+
+      - name: Restore Cargo cache
+        uses: actions/cache@v5
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            ${{ env.CARGO_TARGET_DIR }}
+          key: ${{ runner.os }}-${{ runner.arch }}-rust-pr-${{ matrix.crate }}-${{ steps.toolchain.outputs.cachekey }}-${{ hashFiles(format('Helper/{0}_src/Cargo.toml', matrix.crate)) }}
+          restore-keys: |
+            ${{ runner.os }}-${{ runner.arch }}-rust-pr-${{ matrix.crate }}-${{ steps.toolchain.outputs.cachekey }}-
+
+      - name: Build ${{ matrix.crate }}
+        working-directory: Helper/${{ matrix.crate }}_src
+        run: cargo build --target x86_64-pc-windows-msvc
diff --git a/Helper/Format-Ahk.ps1 b/Helper/Format-Ahk.ps1
index c129fbfe..5f66265c 100644
--- a/Helper/Format-Ahk.ps1
+++ b/Helper/Format-Ahk.ps1
@@ -30,6 +30,10 @@
     Use the .ahk files staged for commit. With -Check, the staged content is
     checked (used by Helper\hooks\pre-commit).
 
+.PARAMETER Base
+    Use the .ahk files changed since the branch left this git ref, for example
+    origin/main (used by .github/workflows/ahk-format.yml).
+
 .PARAMETER Test
     Run the formatter's own tests in Helper\ahkfmt-tests.
 
@@ -44,6 +48,7 @@
     .\Helper\Format-Ahk.ps1 Scripts\1.ahk    # format one file
     .\Helper\Format-Ahk.ps1 -Check           # report files that need formatting
     .\Helper\Format-Ahk.ps1 -Staged          # format the files staged for commit
+    .\Helper\Format-Ahk.ps1 -Check -Base origin/main   # check the files this branch changed
 
 .NOTES
     Exit codes: 0 = ok, 1 = files need formatting (-Check) or tests failed,
@@ -55,6 +60,7 @@ param(
     [string[]]$Path,
     [switch]$Check,
     [switch]$Staged,
+    [string]$Base,
     [switch]$Test,
     [switch]$Stdin
 )
@@ -65,6 +71,7 @@ $ErrorActionPreference = 'Stop'
 $RepoRoot = (Resolve-Path (Join-Path $PSScriptRoot '..')).Path
 $ExcludeFile = Join-Path $PSScriptRoot 'ahkfmt-exclude.list'
 $TestDir = Join-Path $PSScriptRoot 'ahkfmt-tests'
+$GitHubActions = $env:GITHUB_ACTIONS -eq 'true'
 $IndentUnit = '    '
 
 # Analysis only works on the code part of a line: strings emptied, comment removed.
@@ -483,6 +490,10 @@ function Get-TargetFiles {
         $names = Invoke-Git @('diff', '--cached', '--name-only', '--diff-filter=ACMR', '--', '*.ahk')
         return @($names | Where-Object { $_ -and -not (Test-Excluded $_ $excludes) })
     }
+    if ($Base) {
+        $names = Invoke-Git @('diff', '--name-only', '--diff-filter=ACMR', "$Base...HEAD", '--', '*.ahk')
+        return @($names | Where-Object { $_ -and -not (Test-Excluded $_ $excludes) })
+    }
     if (-not $Path) {
         $names = Invoke-Git @('ls-files', '--', '*.ahk')
         return @($names | Where-Object { $_ -and -not (Test-Excluded $_ $excludes) })
@@ -590,6 +601,7 @@ foreach ($relative in Get-TargetFiles) {
         if ($Check) {
             $needsFormat++
             Write-Host "Needs formatting: $relative (line $line)"
+            if ($GitHubActions) { Write-Host "::error file=$relative,line=$line::Not formatted. Run .\Helper\Format-Ahk.ps1 $relative" }
         }
         else {
             [IO.File]::WriteAllBytes($fullPath, (Get-AhkBytes $file $lines))
@@ -600,12 +612,14 @@ foreach ($relative in Get-TargetFiles) {
     catch {
         $errors++
         Write-Host "Skipped: ${relative}: $($_.Exception.Message)"
+        if ($GitHubActions) { Write-Host "::error file=$relative::Could not be formatted: $($_.Exception.Message)" }
     }
 }
 
 if ($Check -and $needsFormat) {
     $hint = '.\Helper\Format-Ahk.ps1'
     if ($Staged) { $hint += ' -Staged' }
+    if ($Base) { $hint += " -Base $Base" }
     Write-Host "$needsFormat file(s) need formatting. Run $hint and add the changes."
 }
 elseif (-not $Check) {