diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..3d78727
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,56 @@
+name: CI
+
+on:
+  # Run on pushes to main (e.g. merges) and on every PR. Limiting push to main
+  # avoids double runs on branches that also have an open PR.
+  push:
+    branches: [main]
+  pull_request:
+
+# Cancel superseded runs for the same branch/PR to save resources.
+concurrency:
+  group: ci-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  lint:
+    name: Lint (gofmt + vet)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+          cache: true
+      - name: Check formatting
+        run: |
+          unformatted="$(gofmt -l .)"
+          if [ -n "$unformatted" ]; then
+            echo "The following files are not gofmt-formatted:"
+            echo "$unformatted"
+            echo "Run: gofmt -w ."
+            exit 1
+          fi
+      - name: go vet
+        run: go vet ./...
+
+  test:
+    name: Build & test
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    steps:
+      - uses: actions/checkout@v6
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+          cache: true
+      - name: Build
+        run: go build ./...
+      - name: Test
+        run: go test -race ./...
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..7235c47
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,7 @@
+# Built binary
+/php-debugger
+/php-debugger.exe
+
+# Go build/test artifacts
+*.test
+*.out
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..341c690
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,10 @@
+module github.com/php-debugger/installer
+
+go 1.25.6
+
+require github.com/spf13/cobra v1.10.2
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..a6ee3e0
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,10 @@
+github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
+github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/spf13/cobra v1.10.2 h1:DMTTonx5m65Ic0GOoRY2c16WCbHxOOw6xxezuLaBpcU=
+github.com/spf13/cobra v1.10.2/go.mod h1:7C1pvHqHw5A4vrJfjNwvOdzYu0Gml16OCs2GRiTUUS4=
+github.com/spf13/pflag v1.0.9 h1:9exaQaMOCwffKiiiYk6/BndUBv+iRViNW+4lEMi0PvY=
+github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
diff --git a/internal/cli/install.go b/internal/cli/install.go
new file mode 100644
index 0000000..0100913
--- /dev/null
+++ b/internal/cli/install.go
@@ -0,0 +1,42 @@
+package cli
+
+import "github.com/spf13/cobra"
+
+// installOptions holds flags specific to the install command.
+type installOptions struct {
+	// PHPVersion selects the PHP version to install (e.g. "8.3"); empty means
+	// the latest available in the release. Interpreter installs only.
+	PHPVersion string
+	// ZTS installs the thread-safe build; default is non-thread-safe.
+	// Interpreter installs only.
+	ZTS bool
+	// ExtensionOnly installs just the debugger extension into the current PHP
+	// instead of a full interpreter.
+	ExtensionOnly bool
+}
+
+func newInstallCmd() *cobra.Command {
+	opts := &installOptions{}
+
+	cmd := &cobra.Command{
+		Use:   "install",
+		Short: "Install the PHP debugger interpreter (default) or just the extension",
+		Long: "Install a self-contained PHP interpreter with the debugger compiled in\n" +
+			"(default), or, with --extension-only, install just the debugger extension\n" +
+			"into the currently active PHP.",
+		Args: cobra.NoArgs,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return errNotImplemented("install")
+		},
+	}
+
+	f := cmd.Flags()
+	f.StringVarP(&opts.PHPVersion, "php", "p", "",
+		"PHP version to install, e.g. 8.3 (default: latest available; interpreter only)")
+	f.BoolVarP(&opts.ZTS, "zts", "z", false,
+		"install the thread-safe (ZTS) build; default is non-thread-safe (interpreter only)")
+	f.BoolVarP(&opts.ExtensionOnly, "extension-only", "e", false,
+		"install only the debugger extension into the current PHP")
+
+	return cmd
+}
diff --git a/internal/cli/root.go b/internal/cli/root.go
new file mode 100644
index 0000000..b5ab37a
--- /dev/null
+++ b/internal/cli/root.go
@@ -0,0 +1,64 @@
+package cli
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+// GlobalOptions holds flags shared by every subcommand.
+type GlobalOptions struct {
+	// User selects the no-sudo, per-user install scope instead of the default
+	// system-wide scope (/opt on Linux/macOS, Program Files on Windows).
+	User bool
+	// Yes assumes "yes" for every interactive confirmation (for CI).
+	Yes bool
+	// Verbose enables extra diagnostic output.
+	Verbose bool
+}
+
+var globalOpts GlobalOptions
+
+func newRootCmd() *cobra.Command {
+	rootCmd := &cobra.Command{
+		Use:   "php-debugger",
+		Short: "Install and manage the PHP debugger",
+		Long: "php-debugger installs the PHP debugger from the php-debugger/php-debugger\n" +
+			"GitHub releases: either a self-contained PHP interpreter with the debugger\n" +
+			"compiled in (default), or the debugger extension for an existing PHP.",
+		SilenceUsage:  true,
+		SilenceErrors: true,
+	}
+
+	pf := rootCmd.PersistentFlags()
+	pf.BoolVarP(&globalOpts.User, "user", "u", false,
+		"install into a per-user directory (no sudo); default is system-wide")
+	pf.BoolVarP(&globalOpts.Yes, "yes", "y", false,
+		"assume yes for all prompts (non-interactive)")
+	pf.BoolVarP(&globalOpts.Verbose, "verbose", "V", false,
+		"enable verbose output")
+
+	rootCmd.AddCommand(
+		newInstallCmd(),
+		newUpdateCmd(),
+		newUninstallCmd(),
+		newSwitchCmd(),
+	)
+
+	return rootCmd
+}
+
+// Execute runs the root command and exits the process with an appropriate code.
+func Execute() {
+	if err := newRootCmd().Execute(); err != nil {
+		fmt.Fprintln(os.Stderr, "Error:", err)
+		os.Exit(1)
+	}
+}
+
+// errNotImplemented is returned by subcommand stubs until they are built out in
+// later steps of the roadmap.
+func errNotImplemented(name string) error {
+	return fmt.Errorf("%q is not implemented yet", name)
+}
diff --git a/internal/cli/switch.go b/internal/cli/switch.go
new file mode 100644
index 0000000..f15e131
--- /dev/null
+++ b/internal/cli/switch.go
@@ -0,0 +1,30 @@
+package cli
+
+import "github.com/spf13/cobra"
+
+// switchOptions holds flags specific to the switch command.
+type switchOptions struct {
+	// ZTS selects the thread-safe variant of the target version.
+	ZTS bool
+}
+
+func newSwitchCmd() *cobra.Command {
+	opts := &switchOptions{}
+
+	cmd := &cobra.Command{
+		Use:   "switch <version>",
+		Short: "Switch the active PHP version (installing it first if needed)",
+		Long: "Point the active PHP symlink at the given version (and optionally its\n" +
+			"thread-safe variant). If that variant is not installed yet, it is installed\n" +
+			"first.",
+		Args: cobra.ExactArgs(1),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return errNotImplemented("switch")
+		},
+	}
+
+	cmd.Flags().BoolVarP(&opts.ZTS, "zts", "z", false,
+		"select the thread-safe (ZTS) variant of the target version")
+
+	return cmd
+}
diff --git a/internal/cli/uninstall.go b/internal/cli/uninstall.go
new file mode 100644
index 0000000..431d4dd
--- /dev/null
+++ b/internal/cli/uninstall.go
@@ -0,0 +1,34 @@
+package cli
+
+import "github.com/spf13/cobra"
+
+// uninstallOptions holds flags specific to the uninstall command.
+type uninstallOptions struct {
+	// Extension uninstalls the debugger extension.
+	Extension bool
+	// Interpreter uninstalls a debugger interpreter (optionally a specific
+	// version given as a positional argument).
+	Interpreter bool
+}
+
+func newUninstallCmd() *cobra.Command {
+	opts := &uninstallOptions{}
+
+	cmd := &cobra.Command{
+		Use:   "uninstall [version]",
+		Short: "Uninstall the interpreter or extension, restoring any backup",
+		Long: "Remove a debugger interpreter (optionally a specific version) or the\n" +
+			"debugger extension. If a backup of a previously replaced interpreter exists,\n" +
+			"it is restored.",
+		Args: cobra.MaximumNArgs(1),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return errNotImplemented("uninstall")
+		},
+	}
+
+	f := cmd.Flags()
+	f.BoolVarP(&opts.Extension, "extension", "e", false, "uninstall the debugger extension")
+	f.BoolVarP(&opts.Interpreter, "interpreter", "i", false, "uninstall the debugger interpreter")
+
+	return cmd
+}
diff --git a/internal/cli/update.go b/internal/cli/update.go
new file mode 100644
index 0000000..9171162
--- /dev/null
+++ b/internal/cli/update.go
@@ -0,0 +1,33 @@
+package cli
+
+import "github.com/spf13/cobra"
+
+// updateOptions holds flags specific to the update command.
+type updateOptions struct {
+	// Extension updates the installed debugger extension.
+	Extension bool
+	// Interpreter updates the active debugger interpreter.
+	Interpreter bool
+}
+
+func newUpdateCmd() *cobra.Command {
+	opts := &updateOptions{}
+
+	cmd := &cobra.Command{
+		Use:   "update",
+		Short: "Update the installed interpreter or extension to the latest release",
+		Long: "Re-install the currently active interpreter (or the extension) against the\n" +
+			"latest release. Use --extension or --interpreter to disambiguate when both\n" +
+			"are installed.",
+		Args: cobra.NoArgs,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return errNotImplemented("update")
+		},
+	}
+
+	f := cmd.Flags()
+	f.BoolVarP(&opts.Extension, "extension", "e", false, "update the debugger extension")
+	f.BoolVarP(&opts.Interpreter, "interpreter", "i", false, "update the debugger interpreter")
+
+	return cmd
+}
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..90ce896
--- /dev/null
+++ b/main.go
@@ -0,0 +1,9 @@
+// Command php-debugger installs and manages the PHP debugger from the
+// php-debugger/php-debugger GitHub releases.
+package main
+
+import "github.com/php-debugger/installer/internal/cli"
+
+func main() {
+	cli.Execute()
+}