diff --git a/SPECS.md b/SPECS.md
index 64c7c9f..722baed 100644
--- a/SPECS.md
+++ b/SPECS.md
@@ -6,7 +6,7 @@ A terminal UI to search for movies and series, add them to Radarr / Sonarr, and
 - **TUI library:** [tview](https://github.com/rivo/tview) (on top of tcell)
 - **License:** MIT
 - **Module:** `git.stinnesbeck.com/nils/arr-tui`
-- **Status:** M0 done
+- **Status:** M1 done
 
 ## 1. Goals
 
@@ -181,7 +181,7 @@ The file should be created with mode `0600`; warn if it is more permissive. API
 ## 9. Milestones
 
 - [x] **M0** — Project skeleton: `go mod init`, config loading, empty tview app with tabs and status bar.
-- [ ] **M1** — Radarr client: system status, lookup, quality profiles, root folders, add movie.
+- [x] **M1** — Radarr client: system status, lookup, quality profiles, root folders, add movie.
 - [ ] **M2** — Movie search + add flow in the UI.
 - [ ] **M3** — Sonarr client and series search + add flow.
 - [ ] **M4** — SABnzbd client and Downloads view (queue + history) with live updates and pause/resume/delete.
diff --git a/internal/arr/client.go b/internal/arr/client.go
new file mode 100644
index 0000000..63d93a4
--- /dev/null
+++ b/internal/arr/client.go
@@ -0,0 +1,124 @@
+// Package arr contains the HTTP client and types shared by the Radarr and Sonarr clients.
+package arr
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+// Client is a minimal JSON client for the Radarr/Sonarr v3 API.
+type Client struct {
+	baseURL string
+	apiKey  string
+	http    *http.Client
+}
+
+// NewClient returns a client for the instance at baseURL (without /api/v3).
+func NewClient(baseURL, apiKey string) *Client {
+	return &Client{
+		baseURL: strings.TrimRight(baseURL, "/"),
+		apiKey:  apiKey,
+		http:    &http.Client{Timeout: 30 * time.Second},
+	}
+}
+
+// APIError is returned for non-2xx responses.
+type APIError struct {
+	Status  int
+	Message string
+}
+
+func (e *APIError) Error() string {
+	if e.Message == "" {
+		return fmt.Sprintf("unexpected response: HTTP %d", e.Status)
+	}
+	return fmt.Sprintf("HTTP %d: %s", e.Status, e.Message)
+}
+
+// Do sends a request to /api/v3/<path>. body (if non-nil) is JSON-encoded and
+// the response is decoded into out (if non-nil).
+func (c *Client) Do(ctx context.Context, method, path string, query url.Values, body, out any) error {
+	u := c.baseURL + "/api/v3/" + strings.TrimLeft(path, "/")
+	if len(query) > 0 {
+		u += "?" + query.Encode()
+	}
+
+	var rd io.Reader
+	if body != nil {
+		b, err := json.Marshal(body)
+		if err != nil {
+			return fmt.Errorf("encoding request: %w", err)
+		}
+		rd = bytes.NewReader(b)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, method, u, rd)
+	if err != nil {
+		return err
+	}
+	req.Header.Set("X-Api-Key", c.apiKey)
+	req.Header.Set("Accept", "application/json")
+	if body != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
+
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return stripURL(err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode > 299 {
+		return &APIError{Status: resp.StatusCode, Message: errorMessage(resp.Body)}
+	}
+	if out == nil {
+		return nil
+	}
+	if err := json.NewDecoder(resp.Body).Decode(out); err != nil {
+		return fmt.Errorf("decoding response: %w", err)
+	}
+	return nil
+}
+
+// stripURL drops the request URL from transport errors so nothing sensitive
+// (e.g. a proxy-added key) ends up in the UI; the host stays in the message.
+func stripURL(err error) error {
+	var ue *url.Error
+	if errors.As(err, &ue) {
+		return fmt.Errorf("%s: %w", ue.Op, ue.Err)
+	}
+	return err
+}
+
+// errorMessage extracts a readable message from Radarr/Sonarr error bodies,
+// which are either {"message": "..."} or a list of validation failures.
+func errorMessage(r io.Reader) string {
+	data, _ := io.ReadAll(io.LimitReader(r, 64<<10))
+
+	var single struct {
+		Message string `json:"message"`
+	}
+	if json.Unmarshal(data, &single) == nil && single.Message != "" {
+		return single.Message
+	}
+	var list []struct {
+		PropertyName string `json:"propertyName"`
+		ErrorMessage string `json:"errorMessage"`
+	}
+	if json.Unmarshal(data, &list) == nil && len(list) > 0 {
+		msgs := make([]string, 0, len(list))
+		for _, e := range list {
+			msgs = append(msgs, e.ErrorMessage)
+		}
+		return strings.Join(msgs, "; ")
+	}
+	return strings.TrimSpace(string(data[:min(len(data), 200)]))
+}
diff --git a/internal/arr/types.go b/internal/arr/types.go
new file mode 100644
index 0000000..bb52238
--- /dev/null
+++ b/internal/arr/types.go
@@ -0,0 +1,54 @@
+package arr
+
+import (
+	"context"
+	"net/http"
+)
+
+// SystemStatus is the subset of /system/status we use.
+type SystemStatus struct {
+	AppName string `json:"appName"`
+	Version string `json:"version"`
+}
+
+// QualityProfile is a Radarr/Sonarr quality profile.
+type QualityProfile struct {
+	ID   int    `json:"id"`
+	Name string `json:"name"`
+}
+
+// RootFolder is a configured library root.
+type RootFolder struct {
+	ID         int    `json:"id"`
+	Path       string `json:"path"`
+	FreeSpace  int64  `json:"freeSpace"`
+	Accessible bool   `json:"accessible"`
+}
+
+// Image is a poster/fanart reference.
+type Image struct {
+	CoverType string `json:"coverType"`
+	URL       string `json:"url,omitempty"`
+	RemoteURL string `json:"remoteUrl,omitempty"`
+}
+
+// SystemStatus fetches /system/status.
+func (c *Client) SystemStatus(ctx context.Context) (SystemStatus, error) {
+	var s SystemStatus
+	err := c.Do(ctx, http.MethodGet, "system/status", nil, nil, &s)
+	return s, err
+}
+
+// QualityProfiles lists quality profiles.
+func (c *Client) QualityProfiles(ctx context.Context) ([]QualityProfile, error) {
+	var p []QualityProfile
+	err := c.Do(ctx, http.MethodGet, "qualityprofile", nil, nil, &p)
+	return p, err
+}
+
+// RootFolders lists root folders.
+func (c *Client) RootFolders(ctx context.Context) ([]RootFolder, error) {
+	var f []RootFolder
+	err := c.Do(ctx, http.MethodGet, "rootfolder", nil, nil, &f)
+	return f, err
+}
diff --git a/internal/radarr/radarr.go b/internal/radarr/radarr.go
new file mode 100644
index 0000000..92de9d1
--- /dev/null
+++ b/internal/radarr/radarr.go
@@ -0,0 +1,142 @@
+// Package radarr is a client for the Radarr v3 API.
+package radarr
+
+import (
+	"context"
+	"net/http"
+	"net/url"
+	"strconv"
+
+	"git.stinnesbeck.com/nils/arr-tui/internal/arr"
+)
+
+// Client talks to a Radarr instance. The embedded arr.Client provides
+// SystemStatus, QualityProfiles and RootFolders.
+type Client struct {
+	*arr.Client
+}
+
+// NewClient returns a Radarr client.
+func NewClient(baseURL, apiKey string) *Client {
+	return &Client{arr.NewClient(baseURL, apiKey)}
+}
+
+// Ratings holds the per-source ratings Radarr reports.
+type Ratings struct {
+	IMDB           *Rating `json:"imdb,omitempty"`
+	TMDB           *Rating `json:"tmdb,omitempty"`
+	Metacritic     *Rating `json:"metacritic,omitempty"`
+	RottenTomatoes *Rating `json:"rottenTomatoes,omitempty"`
+}
+
+// Rating is a single rating value.
+type Rating struct {
+	Votes int     `json:"votes"`
+	Value float64 `json:"value"`
+}
+
+// Movie is a lookup result or library movie. ID is 0 when the movie is not
+// in the library yet.
+type Movie struct {
+	ID               int         `json:"id"`
+	Title            string      `json:"title"`
+	OriginalTitle    string      `json:"originalTitle,omitempty"`
+	Year             int         `json:"year"`
+	Overview         string      `json:"overview,omitempty"`
+	Runtime          int         `json:"runtime"`
+	Genres           []string    `json:"genres,omitempty"`
+	Studio           string      `json:"studio,omitempty"`
+	Status           string      `json:"status,omitempty"`
+	TMDBID           int         `json:"tmdbId"`
+	IMDBID           string      `json:"imdbId,omitempty"`
+	TitleSlug        string      `json:"titleSlug,omitempty"`
+	Images           []arr.Image `json:"images,omitempty"`
+	Ratings          Ratings     `json:"ratings"`
+	Monitored        bool        `json:"monitored"`
+	HasFile          bool        `json:"hasFile"`
+	QualityProfileID int         `json:"qualityProfileId"`
+}
+
+// InLibrary reports whether the movie has already been added to Radarr.
+func (m Movie) InLibrary() bool { return m.ID != 0 }
+
+// Rating returns the best available rating (IMDb, then TMDb), or 0.
+func (m Movie) Rating() float64 {
+	switch {
+	case m.Ratings.IMDB != nil && m.Ratings.IMDB.Value > 0:
+		return m.Ratings.IMDB.Value
+	case m.Ratings.TMDB != nil:
+		return m.Ratings.TMDB.Value
+	}
+	return 0
+}
+
+// Lookup searches for movies by free text ("The Matrix"), "tmdb:603" or "imdb:tt0133093".
+func (c *Client) Lookup(ctx context.Context, term string) ([]Movie, error) {
+	var movies []Movie
+	err := c.Do(ctx, http.MethodGet, "movie/lookup", url.Values{"term": {term}}, nil, &movies)
+	return movies, err
+}
+
+// Movies lists the movies in the library.
+func (c *Client) Movies(ctx context.Context) ([]Movie, error) {
+	var movies []Movie
+	err := c.Do(ctx, http.MethodGet, "movie", nil, nil, &movies)
+	return movies, err
+}
+
+// AddOptions are the choices from the add form.
+type AddOptions struct {
+	QualityProfileID    int
+	RootFolderPath      string
+	Monitored           bool
+	SearchNow           bool
+	MinimumAvailability string // "announced", "inCinemas" or "released"; defaults to "released"
+}
+
+type addMovieRequest struct {
+	Title               string      `json:"title"`
+	Year                int         `json:"year"`
+	TMDBID              int         `json:"tmdbId"`
+	TitleSlug           string      `json:"titleSlug,omitempty"`
+	Images              []arr.Image `json:"images,omitempty"`
+	QualityProfileID    int         `json:"qualityProfileId"`
+	RootFolderPath      string      `json:"rootFolderPath"`
+	Monitored           bool        `json:"monitored"`
+	MinimumAvailability string      `json:"minimumAvailability"`
+	AddOptions          struct {
+		SearchForMovie bool `json:"searchForMovie"`
+	} `json:"addOptions"`
+}
+
+// AddMovie adds a lookup result to Radarr and returns the created movie.
+func (c *Client) AddMovie(ctx context.Context, m Movie, opts AddOptions) (Movie, error) {
+	req := addMovieRequest{
+		Title:               m.Title,
+		Year:                m.Year,
+		TMDBID:              m.TMDBID,
+		TitleSlug:           m.TitleSlug,
+		Images:              m.Images,
+		QualityProfileID:    opts.QualityProfileID,
+		RootFolderPath:      opts.RootFolderPath,
+		Monitored:           opts.Monitored,
+		MinimumAvailability: opts.MinimumAvailability,
+	}
+	if req.MinimumAvailability == "" {
+		req.MinimumAvailability = "released"
+	}
+	req.AddOptions.SearchForMovie = opts.SearchNow
+
+	var created Movie
+	err := c.Do(ctx, http.MethodPost, "movie", nil, req, &created)
+	return created, err
+}
+
+// SearchMovie triggers an automatic search for an existing library movie.
+func (c *Client) SearchMovie(ctx context.Context, movieID int) error {
+	body := map[string]any{"name": "MoviesSearch", "movieIds": []int{movieID}}
+	return c.Do(ctx, http.MethodPost, "command", nil, body, nil)
+}
+
+// TMDBTerm builds a lookup term for a TMDb id.
+func TMDBTerm(tmdbID int) string { return "tmdb:" + strconv.Itoa(tmdbID) }
diff --git a/internal/radarr/radarr_test.go b/internal/radarr/radarr_test.go
new file mode 100644
index 0000000..512ae5d
--- /dev/null
+++ b/internal/radarr/radarr_test.go
@@ -0,0 +1,150 @@
+package radarr
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"git.stinnesbeck.com/nils/arr-tui/internal/arr"
+)
+
+const lookupJSON = `[
+  {"id":0,"title":"The Matrix","year":1999,"tmdbId":603,"imdbId":"tt0133093","titleSlug":"the-matrix-603",
+   "runtime":136,"genres":["Action","Science Fiction"],"overview":"A hacker...",
+   "images":[{"coverType":"poster","remoteUrl":"https://img/p.jpg"}],
+   "ratings":{"imdb":{"votes":2000000,"value":8.7},"tmdb":{"votes":1,"value":8.2}}},
+  {"id":42,"title":"The Matrix Reloaded","year":2003,"tmdbId":604,"ratings":{"tmdb":{"votes":1,"value":7.0}}}
+]`
+
+func newTestClient(t *testing.T, h http.HandlerFunc) *Client {
+	t.Helper()
+	srv := httptest.NewServer(h)
+	t.Cleanup(srv.Close)
+	return NewClient(srv.URL, "secret")
+}
+
+func TestLookup(t *testing.T) {
+	c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v3/movie/lookup" || r.URL.Query().Get("term") != "the matrix" {
+			t.Errorf("unexpected request %s", r.URL)
+		}
+		if r.Header.Get("X-Api-Key") != "secret" {
+			t.Error("missing api key header")
+		}
+		w.Write([]byte(lookupJSON))
+	})
+	movies, err := c.Lookup(context.Background(), "the matrix")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(movies) != 2 {
+		t.Fatalf("got %d movies", len(movies))
+	}
+	if movies[0].InLibrary() || !movies[1].InLibrary() {
+		t.Error("InLibrary wrong")
+	}
+	if movies[0].Rating() != 8.7 || movies[1].Rating() != 7.0 {
+		t.Errorf("ratings: %v %v", movies[0].Rating(), movies[1].Rating())
+	}
+	if movies[0].Images[0].RemoteURL == "" {
+		t.Error("image not decoded")
+	}
+}
+
+func TestAddMovie(t *testing.T) {
+	var got map[string]any
+	c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost || r.URL.Path != "/api/v3/movie" {
+			t.Errorf("unexpected request %s %s", r.Method, r.URL)
+		}
+		json.NewDecoder(r.Body).Decode(&got)
+		w.WriteHeader(http.StatusCreated)
+		w.Write([]byte(`{"id":7,"title":"The Matrix","tmdbId":603}`))
+	})
+	m := Movie{Title: "The Matrix", Year: 1999, TMDBID: 603, TitleSlug: "the-matrix-603"}
+	created, err := c.AddMovie(context.Background(), m, AddOptions{
+		QualityProfileID: 4, RootFolderPath: "/movies", Monitored: true, SearchNow: true,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if created.ID != 7 {
+		t.Errorf("id = %d", created.ID)
+	}
+	if got["tmdbId"] != float64(603) || got["qualityProfileId"] != float64(4) ||
+		got["rootFolderPath"] != "/movies" || got["monitored"] != true ||
+		got["minimumAvailability"] != "released" {
+		t.Errorf("request body = %v", got)
+	}
+	if ao, _ := got["addOptions"].(map[string]any); ao["searchForMovie"] != true {
+		t.Errorf("addOptions = %v", got["addOptions"])
+	}
+}
+
+func TestAPIErrors(t *testing.T) {
+	tests := map[string]struct {
+		status int
+		body   string
+		want   string
+	}{
+		"message":    {http.StatusBadRequest, `{"message":"bad thing"}`, "HTTP 400: bad thing"},
+		"validation": {http.StatusBadRequest, `[{"propertyName":"TmdbId","errorMessage":"This movie has already been added"}]`, "HTTP 400: This movie has already been added"},
+		"unauth":     {http.StatusUnauthorized, ``, "unexpected response: HTTP 401"},
+	}
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(tc.status)
+				w.Write([]byte(tc.body))
+			})
+			_, err := c.AddMovie(context.Background(), Movie{}, AddOptions{})
+			var apiErr *arr.APIError
+			if !errors.As(err, &apiErr) || apiErr.Status != tc.status || err.Error() != tc.want {
+				t.Fatalf("err = %v, want %q", err, tc.want)
+			}
+		})
+	}
+}
+
+func TestSharedEndpoints(t *testing.T) {
+	c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/api/v3/system/status":
+			w.Write([]byte(`{"appName":"Radarr","version":"5.0.0"}`))
+		case "/api/v3/qualityprofile":
+			w.Write([]byte(`[{"id":1,"name":"Any"},{"id":4,"name":"HD-1080p"}]`))
+		case "/api/v3/rootfolder":
+			w.Write([]byte(`[{"id":1,"path":"/movies","freeSpace":1000,"accessible":true}]`))
+		default:
+			t.Errorf("unexpected %s", r.URL)
+		}
+	})
+	ctx := context.Background()
+	if s, err := c.SystemStatus(ctx); err != nil || s.AppName != "Radarr" {
+		t.Errorf("status = %+v, %v", s, err)
+	}
+	if p, err := c.QualityProfiles(ctx); err != nil || len(p) != 2 || p[1].Name != "HD-1080p" {
+		t.Errorf("profiles = %+v, %v", p, err)
+	}
+	if f, err := c.RootFolders(ctx); err != nil || len(f) != 1 || f[0].Path != "/movies" {
+		t.Errorf("folders = %+v, %v", f, err)
+	}
+}
+
+func TestSearchMovie(t *testing.T) {
+	var got map[string]any
+	c := newTestClient(t, func(w http.ResponseWriter, r *http.Request) {
+		json.NewDecoder(r.Body).Decode(&got)
+		w.WriteHeader(http.StatusCreated)
+		w.Write([]byte(`{}`))
+	})
+	if err := c.SearchMovie(context.Background(), 7); err != nil {
+		t.Fatal(err)
+	}
+	if got["name"] != "MoviesSearch" {
+		t.Errorf("body = %v", got)
+	}
+}