diff --git a/internal/modules/shellconfig/shellconfig.go b/internal/modules/shellconfig/shellconfig.go
new file mode 100644
index 0000000..45b793a
--- /dev/null
+++ b/internal/modules/shellconfig/shellconfig.go
@@ -0,0 +1,90 @@
+// Package shellconfig writes marker-delimited blocks into rc files.
+package shellconfig
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/MDietermann/ArduinoArchSetup/internal/config"
+	"github.com/MDietermann/ArduinoArchSetup/internal/module"
+	"github.com/MDietermann/ArduinoArchSetup/internal/platform"
+)
+
+type Module struct{ cfg config.ShellConfigSection }
+
+func New(cfg config.ShellConfigSection) Module { return Module{cfg: cfg} }
+
+type state struct{ Missing []config.ShellConfigBlock }
+
+func (Module) Meta() module.Meta {
+	return module.Meta{ID: "shellconfig", Name: "Shell config blocks", Description: "Write archduino blocks into rc files."}
+}
+
+func resolveFile(name string) (string, error) {
+	h, err := os.UserHomeDir()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(h, name), nil
+}
+
+func (m Module) Detect(ctx context.Context) (module.State, error) {
+	var missing []config.ShellConfigBlock
+	for _, b := range m.cfg.Blocks {
+		p, err := resolveFile(b.File)
+		if err != nil {
+			return nil, err
+		}
+		has, err := platform.HasBlock(p, b.Name)
+		if err != nil {
+			return nil, err
+		}
+		if !has {
+			missing = append(missing, b)
+		}
+	}
+	return state{Missing: missing}, nil
+}
+
+func (m Module) Plan(ctx context.Context, cur module.State) (module.Plan, error) {
+	s, _ := cur.(state)
+	var actions []module.Action
+	for _, b := range s.Missing {
+		b := b
+		actions = append(actions, module.Action{
+			Description: fmt.Sprintf("write block %s into %s", b.Name, b.File),
+			Kind:        module.ActionFileWrite,
+			Exec: func(ctx context.Context) error {
+				p, err := resolveFile(b.File)
+				if err != nil {
+					return err
+				}
+				return platform.EnsureBlock(p, b.Name, b.Content)
+			},
+		})
+	}
+	return module.Plan{Actions: actions}, nil
+}
+
+func (m Module) Apply(ctx context.Context, p module.Plan, r module.Reporter) error {
+	for i, a := range p.Actions {
+		r.Progress(m.Meta().ID, i+1, len(p.Actions), a.Description)
+		if err := a.Exec(ctx); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (m Module) Verify(ctx context.Context) error {
+	st, err := m.Detect(ctx)
+	if err != nil {
+		return err
+	}
+	if miss := st.(state).Missing; len(miss) > 0 {
+		return fmt.Errorf("shell blocks still missing: %d", len(miss))
+	}
+	return nil
+}
diff --git a/internal/modules/shellconfig/shellconfig_test.go b/internal/modules/shellconfig/shellconfig_test.go
new file mode 100644
index 0000000..2292ec5
--- /dev/null
+++ b/internal/modules/shellconfig/shellconfig_test.go
@@ -0,0 +1,58 @@
+package shellconfig
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/MDietermann/ArduinoArchSetup/internal/config"
+	"github.com/MDietermann/ArduinoArchSetup/internal/module"
+)
+
+type nop struct{}
+
+func (nop) Progress(string, int, int, string) {}
+func (nop) Log(string, string)                {}
+
+func TestShellConfigWritesBlocks(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	m := New(config.ShellConfigSection{
+		Blocks: []config.ShellConfigBlock{
+			{Name: "path", File: ".zshrc", Content: `export PATH="$HOME/.local/bin:$PATH"`},
+		},
+	})
+	st, _ := m.Detect(context.Background())
+	p, _ := m.Plan(context.Background(), st)
+	if err := m.Apply(context.Background(), p, nop{}); err != nil {
+		t.Fatal(err)
+	}
+	data, _ := os.ReadFile(filepath.Join(home, ".zshrc"))
+	if !strings.Contains(string(data), ">>> path >>>") {
+		t.Fatalf("block not present: %q", data)
+	}
+	if !strings.Contains(string(data), `export PATH="$HOME/.local/bin:$PATH"`) {
+		t.Fatalf("content missing: %q", data)
+	}
+}
+
+func TestShellConfigIdempotent(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	cfg := config.ShellConfigSection{Blocks: []config.ShellConfigBlock{
+		{Name: "x", File: ".zshrc", Content: "echo x"},
+	}}
+	m := New(cfg)
+	st, _ := m.Detect(context.Background())
+	p, _ := m.Plan(context.Background(), st)
+	_ = m.Apply(context.Background(), p, nop{})
+	st2, _ := m.Detect(context.Background())
+	p2, _ := m.Plan(context.Background(), st2)
+	if !p2.IsEmpty() {
+		t.Fatalf("second plan not empty: %+v", p2.Actions)
+	}
+}
+
+var _ module.Module = Module{}