diff --git a/configuration.nix b/configuration.nix
index 48980b2..a181410 100644
--- a/configuration.nix
+++ b/configuration.nix
@@ -19,6 +19,7 @@
     ./modules/secureboot.nix
     ./modules/no-rgb.nix
     ./modules/security.nix
+    ./modules/arr-init.nix
 
     ./services/postgresql.nix
     ./services/jellyfin.nix
@@ -38,6 +39,7 @@
     ./services/arr/bazarr.nix
     ./services/arr/jellyseerr.nix
     ./services/arr/recyclarr.nix
+    ./services/arr/init.nix
 
     ./services/soulseek.nix
 
diff --git a/flake.nix b/flake.nix
index 3f96036..edd15c6 100644
--- a/flake.nix
+++ b/flake.nix
@@ -222,6 +222,11 @@
         recyclarr = {
           dataDir = services_dir + "/recyclarr";
         };
+
+        media = {
+          moviesDir = torrents_path + "/media/movies";
+          tvDir = torrents_path + "/media/tv";
+        };
       };
 
       pkgs = import nixpkgs {
diff --git a/modules/arr-init.nix b/modules/arr-init.nix
new file mode 100644
index 0000000..26ed0cb
--- /dev/null
+++ b/modules/arr-init.nix
@@ -0,0 +1,492 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  cfg = config.services.arrInit;
+  bazarrCfg = config.services.bazarrInit;
+
+  downloadClientModule = lib.types.submodule {
+    options = {
+      name = lib.mkOption {
+        type = lib.types.str;
+        description = "Display name of the download client (e.g. \"qBittorrent\").";
+        example = "qBittorrent";
+      };
+
+      implementation = lib.mkOption {
+        type = lib.types.str;
+        description = "Implementation identifier for the Servarr API.";
+        example = "QBittorrent";
+      };
+
+      configContract = lib.mkOption {
+        type = lib.types.str;
+        description = "Config contract identifier for the Servarr API.";
+        example = "QBittorrentSettings";
+      };
+
+      protocol = lib.mkOption {
+        type = lib.types.enum [
+          "torrent"
+          "usenet"
+        ];
+        default = "torrent";
+        description = "Download protocol type.";
+      };
+
+      fields = lib.mkOption {
+        type = lib.types.attrsOf lib.types.anything;
+        default = { };
+        description = ''
+          Flat key/value pairs for the download client configuration.
+          These are converted to the API's [{name, value}] array format.
+        '';
+        example = {
+          host = "192.168.15.1";
+          port = 6011;
+          useSsl = false;
+          tvCategory = "tvshows";
+        };
+      };
+    };
+  };
+
+  syncedAppModule = lib.types.submodule {
+    options = {
+      name = lib.mkOption {
+        type = lib.types.str;
+        description = "Display name of the application to sync (e.g. \"Sonarr\").";
+        example = "Sonarr";
+      };
+
+      implementation = lib.mkOption {
+        type = lib.types.str;
+        description = "Implementation identifier for the Prowlarr application API.";
+        example = "Sonarr";
+      };
+
+      configContract = lib.mkOption {
+        type = lib.types.str;
+        description = "Config contract identifier for the Prowlarr application API.";
+        example = "SonarrSettings";
+      };
+
+      syncLevel = lib.mkOption {
+        type = lib.types.str;
+        default = "fullSync";
+        description = "Sync level for the application.";
+      };
+
+      prowlarrUrl = lib.mkOption {
+        type = lib.types.str;
+        description = "URL of the Prowlarr instance.";
+        example = "http://localhost:9696";
+      };
+
+      baseUrl = lib.mkOption {
+        type = lib.types.str;
+        description = "URL of the target application.";
+        example = "http://localhost:8989";
+      };
+
+      apiKeyFrom = lib.mkOption {
+        type = lib.types.str;
+        description = "Path to the config.xml file to read the API key from at runtime.";
+        example = "/services/sonarr/config.xml";
+      };
+
+      syncCategories = lib.mkOption {
+        type = lib.types.listOf lib.types.int;
+        default = [ ];
+        description = "List of sync category IDs for the application.";
+        example = [
+          5000
+          5010
+          5020
+        ];
+      };
+
+      serviceName = lib.mkOption {
+        type = lib.types.str;
+        description = "Name of the systemd service to depend on for reading the API key.";
+        example = "sonarr";
+      };
+    };
+  };
+
+  instanceModule = lib.types.submodule {
+    options = {
+      enable = lib.mkEnableOption "Servarr application API initialization";
+
+      serviceName = lib.mkOption {
+        type = lib.types.str;
+        description = "Name of the systemd service this init depends on.";
+        example = "sonarr";
+      };
+
+      dataDir = lib.mkOption {
+        type = lib.types.str;
+        description = "Path to the application data directory containing config.xml.";
+        example = "/var/lib/sonarr";
+      };
+
+      port = lib.mkOption {
+        type = lib.types.port;
+        description = "API port of the Servarr application.";
+        example = 8989;
+      };
+
+      apiVersion = lib.mkOption {
+        type = lib.types.str;
+        default = "v3";
+        description = "API version string used in the base URL.";
+      };
+
+      networkNamespacePath = lib.mkOption {
+        type = lib.types.nullOr lib.types.str;
+        default = null;
+        description = "If set, run this init service inside the given network namespace path (e.g. /run/netns/wg).";
+      };
+
+      downloadClients = lib.mkOption {
+        type = lib.types.listOf downloadClientModule;
+        default = [ ];
+        description = "List of download clients to configure via the API.";
+      };
+
+      rootFolders = lib.mkOption {
+        type = lib.types.listOf lib.types.str;
+        default = [ ];
+        description = "List of root folder paths to configure via the API.";
+        example = [
+          "/media/tv"
+          "/media/movies"
+        ];
+      };
+
+      syncedApps = lib.mkOption {
+        type = lib.types.listOf syncedAppModule;
+        default = [ ];
+        description = "Applications to register for indexer sync (Prowlarr only).";
+      };
+    };
+  };
+
+  bazarrProviderModule = lib.types.submodule {
+    options = {
+      enable = lib.mkEnableOption "provider connection";
+
+      dataDir = lib.mkOption {
+        type = lib.types.str;
+        description = "Path to the provider's data directory containing config.xml.";
+        example = "/services/sonarr";
+      };
+
+      port = lib.mkOption {
+        type = lib.types.port;
+        description = "API port of the provider.";
+        example = 8989;
+      };
+
+      serviceName = lib.mkOption {
+        type = lib.types.str;
+        description = "Name of the systemd service to depend on.";
+        example = "sonarr";
+      };
+    };
+  };
+
+  bazarrInitModule = lib.types.submodule {
+    options = {
+      enable = lib.mkEnableOption "Bazarr API initialization";
+
+      dataDir = lib.mkOption {
+        type = lib.types.str;
+        description = "Path to Bazarr's data directory containing config/config.ini.";
+        example = "/services/bazarr";
+      };
+
+      port = lib.mkOption {
+        type = lib.types.port;
+        default = 6767;
+        description = "API port of Bazarr.";
+      };
+
+      sonarr = lib.mkOption {
+        type = bazarrProviderModule;
+        default = {
+          enable = false;
+        };
+        description = "Sonarr provider configuration.";
+      };
+
+      radarr = lib.mkOption {
+        type = bazarrProviderModule;
+        default = {
+          enable = false;
+        };
+        description = "Radarr provider configuration.";
+      };
+    };
+  };
+
+  curl = "${pkgs.curl}/bin/curl";
+  jq = "${pkgs.jq}/bin/jq";
+  grep = "${pkgs.gnugrep}/bin/grep";
+
+  mkDownloadClientPayload =
+    dc:
+    builtins.toJSON {
+      enable = true;
+      protocol = dc.protocol;
+      priority = 1;
+      name = dc.name;
+      implementation = dc.implementation;
+      configContract = dc.configContract;
+      fields = lib.mapAttrsToList (n: v: {
+        name = n;
+        value = v;
+      }) dc.fields;
+      tags = [ ];
+    };
+
+  mkDownloadClientSection = dc: ''
+    # Download client: ${dc.name}
+    echo "Checking download client '${dc.name}'..."
+    EXISTING_DC=$(${curl} -sf "$BASE_URL/downloadclient" -H "X-Api-Key: $API_KEY")
+    if echo "$EXISTING_DC" | ${jq} -e --arg name ${lib.escapeShellArg dc.name} '.[] | select(.name == $name)' > /dev/null 2>&1; then
+      echo "Download client '${dc.name}' already exists, skipping"
+    else
+      echo "Adding download client '${dc.name}'..."
+      ${curl} -sf -X POST "$BASE_URL/downloadclient?forceSave=true" \
+        -H "X-Api-Key: $API_KEY" \
+        -H "Content-Type: application/json" \
+        -d ${lib.escapeShellArg (mkDownloadClientPayload dc)}
+      echo "Download client '${dc.name}' added"
+    fi
+  '';
+
+  mkRootFolderSection = path: ''
+    # Root folder: ${path}
+    echo "Checking root folder '${path}'..."
+    EXISTING_RF=$(${curl} -sf "$BASE_URL/rootfolder" -H "X-Api-Key: $API_KEY")
+    if echo "$EXISTING_RF" | ${jq} -e --arg path ${lib.escapeShellArg path} '.[] | select(.path == $path)' > /dev/null 2>&1; then
+      echo "Root folder '${path}' already exists, skipping"
+    else
+      echo "Adding root folder '${path}'..."
+      ${curl} -sf -X POST "$BASE_URL/rootfolder" \
+        -H "X-Api-Key: $API_KEY" \
+        -H "Content-Type: application/json" \
+        -d ${lib.escapeShellArg (builtins.toJSON { inherit path; })}
+      echo "Root folder '${path}' added"
+    fi
+  '';
+
+  mkSyncedAppSection = app: ''
+    # Synced app: ${app.name}
+    echo "Checking synced app '${app.name}'..."
+    TARGET_API_KEY=$(${grep} -oP '(?<=<ApiKey>)[^<]+' ${lib.escapeShellArg app.apiKeyFrom})
+    EXISTING_APPS=$(${curl} -sf "$BASE_URL/applications" -H "X-Api-Key: $API_KEY")
+    if echo "$EXISTING_APPS" | ${jq} -e --arg name ${lib.escapeShellArg app.name} '.[] | select(.name == $name)' > /dev/null 2>&1; then
+      echo "Synced app '${app.name}' already exists, skipping"
+    else
+      echo "Adding synced app '${app.name}'..."
+      PAYLOAD=$(${jq} -n \
+        --arg name ${lib.escapeShellArg app.name} \
+        --arg implementation ${lib.escapeShellArg app.implementation} \
+        --arg configContract ${lib.escapeShellArg app.configContract} \
+        --arg syncLevel ${lib.escapeShellArg app.syncLevel} \
+        --arg prowlarrUrl ${lib.escapeShellArg app.prowlarrUrl} \
+        --arg baseUrl ${lib.escapeShellArg app.baseUrl} \
+        --arg apiKey "$TARGET_API_KEY" \
+        --argjson syncCategories ${builtins.toJSON app.syncCategories} \
+        '{
+          name: $name,
+          implementation: $implementation,
+          configContract: $configContract,
+          syncLevel: $syncLevel,
+          fields: [
+            {name: "prowlarrUrl", value: $prowlarrUrl},
+            {name: "baseUrl", value: $baseUrl},
+            {name: "apiKey", value: $apiKey},
+            {name: "syncCategories", value: $syncCategories}
+          ],
+          tags: []
+        }')
+      ${curl} -sf -X POST "$BASE_URL/applications?forceSave=true" \
+        -H "X-Api-Key: $API_KEY" \
+        -H "Content-Type: application/json" \
+        -d "$PAYLOAD"
+      echo "Synced app '${app.name}' added"
+    fi
+  '';
+
+  mkInitScript =
+    name: inst:
+    pkgs.writeShellScript "${name}-init" ''
+      set -euo pipefail
+
+      CONFIG_XML="${inst.dataDir}/config.xml"
+
+      if [ ! -f "$CONFIG_XML" ]; then
+        echo "Config file $CONFIG_XML not found, skipping ${name} init"
+        exit 0
+      fi
+
+      API_KEY=$(${grep} -oP '(?<=<ApiKey>)[^<]+' "$CONFIG_XML")
+      BASE_URL="http://localhost:${builtins.toString inst.port}/api/${inst.apiVersion}"
+
+      # Wait for API to become available
+      echo "Waiting for ${name} API..."
+      for i in $(seq 1 90); do
+        if ${curl} -sf "$BASE_URL/system/status" -H "X-Api-Key: $API_KEY" > /dev/null 2>&1; then
+          echo "${name} API is ready"
+          break
+        fi
+        if [ "$i" -eq 90 ]; then
+          echo "${name} API not available after 90 seconds" >&2
+          exit 1
+        fi
+        sleep 1
+      done
+
+      ${lib.concatMapStringsSep "\n" mkDownloadClientSection inst.downloadClients}
+      ${lib.concatMapStringsSep "\n" mkRootFolderSection inst.rootFolders}
+      ${lib.concatMapStringsSep "\n" mkSyncedAppSection inst.syncedApps}
+
+      echo "${name} init complete"
+    '';
+
+  # Get list of service names that syncedApps depend on
+  getSyncedAppDeps = inst: map (app: "${app.serviceName}.service") inst.syncedApps;
+
+  enabledInstances = lib.filterAttrs (_: inst: inst.enable) cfg;
+
+  mkBazarrProviderSection = type: provider: ''
+    # ${type} provider
+    echo "Checking ${type} provider..."
+    PROVIDER_API_KEY=$(${grep} -oP '(?<=<ApiKey>)[^<]+' ${lib.escapeShellArg "${provider.dataDir}/config.xml"})
+    EXISTING=$(${curl} -sf "$BASE_URL/api/${lib.toLower type}" -H "X-API-KEY: $API_KEY")
+    if echo "$EXISTING" | ${jq} -e '. | length > 0' > /dev/null 2>&1; then
+      echo "${type} provider already configured, skipping"
+    else
+      echo "Adding ${type} provider..."
+      PAYLOAD=$(${jq} -n \
+        --arg ip "localhost" \
+        --argjson port ${builtins.toString provider.port} \
+        --arg apikey "$PROVIDER_API_KEY" \
+        --argjson ssl false \
+        --arg base_url "/" \
+        '{ip: $ip, port: $port, apikey: $apikey, ssl: $ssl, base_url: $base_url}')
+      ${curl} -sf -X POST "$BASE_URL/api/${lib.toLower type}" \
+        -H "X-API-KEY: $API_KEY" \
+        -H "Content-Type: application/json" \
+        -d "$PAYLOAD"
+      echo "${type} provider added"
+    fi
+  '';
+
+  mkBazarrInitScript = pkgs.writeShellScript "bazarr-init" ''
+    set -euo pipefail
+
+    CONFIG_INI="${bazarrCfg.dataDir}/config/config.ini"
+
+    if [ ! -f "$CONFIG_INI" ]; then
+      echo "Config file $CONFIG_INI not found, skipping bazarr init"
+      exit 0
+    fi
+
+    API_KEY=$(${grep} -oP '(?<=apikey = )[^\n]+' "$CONFIG_INI")
+    BASE_URL="http://localhost:${builtins.toString bazarrCfg.port}"
+
+    # Wait for API to become available
+    echo "Waiting for Bazarr API..."
+    for i in $(seq 1 90); do
+      if ${curl} -sf "$BASE_URL/api/system/status" -H "X-API-KEY: $API_KEY" > /dev/null 2>&1; then
+        echo "Bazarr API is ready"
+        break
+      fi
+      if [ "$i" -eq 90 ]; then
+        echo "Bazarr API not available after 90 seconds" >&2
+        exit 1
+      fi
+      sleep 1
+    done
+
+    ${lib.optionalString bazarrCfg.sonarr.enable (mkBazarrProviderSection "Sonarr" bazarrCfg.sonarr)}
+    ${lib.optionalString bazarrCfg.radarr.enable (mkBazarrProviderSection "Radarr" bazarrCfg.radarr)}
+
+    echo "Bazarr init complete"
+  '';
+
+  bazarrDeps = [
+    "bazarr.service"
+  ]
+  ++ (lib.optional bazarrCfg.sonarr.enable "${bazarrCfg.sonarr.serviceName}.service")
+  ++ (lib.optional bazarrCfg.radarr.enable "${bazarrCfg.radarr.serviceName}.service");
+in
+{
+  options.services.arrInit = lib.mkOption {
+    type = lib.types.attrsOf instanceModule;
+    default = { };
+    description = ''
+      Attribute set of Servarr application instances to initialize via their APIs.
+      Each instance generates a systemd oneshot service that idempotently configures
+      download clients, root folders, and synced applications.
+    '';
+  };
+
+  options.services.bazarrInit = lib.mkOption {
+    type = bazarrInitModule;
+    default = {
+      enable = false;
+    };
+    description = ''
+      Bazarr API initialization for connecting Sonarr and Radarr providers.
+      Bazarr uses a different API than Servarr applications, so it has its own module.
+    '';
+  };
+
+  config = lib.mkMerge [
+    (lib.mkIf (enabledInstances != { }) {
+      systemd.services = lib.mapAttrs' (
+        name: inst:
+        lib.nameValuePair "${inst.serviceName}-init" {
+          description = "Initialize ${name} API connections";
+          after = [
+            "${inst.serviceName}.service"
+          ]
+          ++ (getSyncedAppDeps inst)
+          ++ (lib.optional (inst.networkNamespacePath != null) "wg.service");
+          requires = [ "${inst.serviceName}.service" ];
+          wantedBy = [ "multi-user.target" ];
+          serviceConfig = {
+            Type = "oneshot";
+            RemainAfterExit = true;
+            ExecStart = "${mkInitScript name inst}";
+          }
+          // lib.optionalAttrs (inst.networkNamespacePath != null) {
+            NetworkNamespacePath = inst.networkNamespacePath;
+          };
+        }
+      ) enabledInstances;
+    })
+
+    (lib.mkIf bazarrCfg.enable {
+      systemd.services.bazarr-init = {
+        description = "Initialize Bazarr API connections";
+        after = bazarrDeps;
+        requires = bazarrDeps;
+        wantedBy = [ "multi-user.target" ];
+        serviceConfig = {
+          Type = "oneshot";
+          RemainAfterExit = true;
+          ExecStart = "${mkBazarrInitScript}";
+        };
+      };
+    })
+  ];
+}
diff --git a/services/arr/init.nix b/services/arr/init.nix
new file mode 100644
index 0000000..f677512
--- /dev/null
+++ b/services/arr/init.nix
@@ -0,0 +1,115 @@
+{ config, service_configs, ... }:
+{
+  services.arrInit = {
+    prowlarr = {
+      enable = true;
+      serviceName = "prowlarr";
+      port = service_configs.ports.prowlarr;
+      dataDir = service_configs.prowlarr.dataDir;
+      apiVersion = "v1";
+      networkNamespacePath = "/run/netns/wg";
+      syncedApps = [
+        {
+          name = "Sonarr";
+          implementation = "Sonarr";
+          configContract = "SonarrSettings";
+          prowlarrUrl = "http://localhost:${builtins.toString service_configs.ports.prowlarr}";
+          baseUrl = "http://${config.vpnNamespaces.wg.bridgeAddress}:${builtins.toString service_configs.ports.sonarr}";
+          apiKeyFrom = "${service_configs.sonarr.dataDir}/config.xml";
+          syncCategories = [
+            5000
+            5010
+            5020
+            5030
+            5040
+            5045
+            5050
+            5090
+          ];
+          serviceName = "sonarr";
+        }
+        {
+          name = "Radarr";
+          implementation = "Radarr";
+          configContract = "RadarrSettings";
+          prowlarrUrl = "http://localhost:${builtins.toString service_configs.ports.prowlarr}";
+          baseUrl = "http://${config.vpnNamespaces.wg.bridgeAddress}:${builtins.toString service_configs.ports.radarr}";
+          apiKeyFrom = "${service_configs.radarr.dataDir}/config.xml";
+          syncCategories = [
+            2000
+            2010
+            2020
+            2030
+            2040
+            2045
+            2050
+            2060
+            2070
+            2080
+          ];
+          serviceName = "radarr";
+        }
+      ];
+    };
+
+    sonarr = {
+      enable = true;
+      serviceName = "sonarr";
+      port = service_configs.ports.sonarr;
+      dataDir = service_configs.sonarr.dataDir;
+      rootFolders = [ service_configs.media.tvDir ];
+      downloadClients = [
+        {
+          name = "qBittorrent";
+          implementation = "QBittorrent";
+          configContract = "QBittorrentSettings";
+          fields = {
+            host = config.vpnNamespaces.wg.namespaceAddress;
+            port = service_configs.ports.torrent;
+            useSsl = false;
+            tvCategory = "tvshows";
+          };
+        }
+      ];
+    };
+
+    radarr = {
+      enable = true;
+      serviceName = "radarr";
+      port = service_configs.ports.radarr;
+      dataDir = service_configs.radarr.dataDir;
+      rootFolders = [ service_configs.media.moviesDir ];
+      downloadClients = [
+        {
+          name = "qBittorrent";
+          implementation = "QBittorrent";
+          configContract = "QBittorrentSettings";
+          fields = {
+            host = config.vpnNamespaces.wg.namespaceAddress;
+            port = service_configs.ports.torrent;
+            useSsl = false;
+            movieCategory = "movies";
+          };
+        }
+      ];
+    };
+  };
+
+  services.bazarrInit = {
+    enable = true;
+    dataDir = service_configs.bazarr.dataDir;
+    port = service_configs.ports.bazarr;
+    sonarr = {
+      enable = true;
+      dataDir = service_configs.sonarr.dataDir;
+      port = service_configs.ports.sonarr;
+      serviceName = "sonarr";
+    };
+    radarr = {
+      enable = true;
+      dataDir = service_configs.radarr.dataDir;
+      port = service_configs.ports.radarr;
+      serviceName = "radarr";
+    };
+  };
+}
diff --git a/services/arr/prowlarr.nix b/services/arr/prowlarr.nix
index c5e9c69..a2ad767 100644
--- a/services/arr/prowlarr.nix
+++ b/services/arr/prowlarr.nix
@@ -19,6 +19,10 @@
     settings.server.port = service_configs.ports.prowlarr;
   };
 
+  systemd.services.prowlarr.serviceConfig = {
+    ExecStartPre = "+${pkgs.coreutils}/bin/chown -R prowlarr /var/lib/prowlarr";
+  };
+
   services.caddy.virtualHosts."prowlarr.${service_configs.https.domain}".extraConfig = ''
     import ${config.age.secrets.caddy_auth.path}
     reverse_proxy ${config.vpnNamespaces.wg.namespaceAddress}:${builtins.toString service_configs.ports.prowlarr}
diff --git a/tests/arr-init.nix b/tests/arr-init.nix
new file mode 100644
index 0000000..ab49200
--- /dev/null
+++ b/tests/arr-init.nix
@@ -0,0 +1,354 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  testPkgs = pkgs.appendOverlays [ (import ../modules/overlays.nix) ];
+in
+testPkgs.testers.runNixOSTest {
+  name = "arr-init";
+
+  nodes.machine =
+    { pkgs, ... }:
+    {
+      imports = [
+        ../modules/arr-init.nix
+      ];
+
+      system.stateVersion = config.system.stateVersion;
+
+      virtualisation.memorySize = 4096;
+
+      environment.systemPackages = with pkgs; [
+        curl
+        jq
+        gnugrep
+      ];
+
+      systemd.services.mock-qbittorrent =
+        let
+          mockQbitScript = pkgs.writeScript "mock-qbittorrent.py" ''
+            import json
+            from http.server import HTTPServer, BaseHTTPRequestHandler
+            from urllib.parse import parse_qs, urlparse
+
+
+            CATEGORIES = {
+                "tv": {"name": "tv", "savePath": "/downloads"},
+                "movies": {"name": "movies", "savePath": "/downloads"},
+            }
+
+
+            class QBitMock(BaseHTTPRequestHandler):
+                def _respond(self, code=200, body=b"Ok.", content_type="text/plain"):
+                    self.send_response(code)
+                    self.send_header("Content-Type", content_type)
+                    self.send_header("Set-Cookie", "SID=mock_session_id; Path=/")
+                    self.end_headers()
+                    self.wfile.write(body if isinstance(body, bytes) else body.encode())
+
+                def do_GET(self):
+                    path = self.path.split("?")[0]
+                    if path == "/api/v2/app/webapiVersion":
+                        self._respond(body=b"2.9.3")
+                    elif path == "/api/v2/app/version":
+                        self._respond(body=b"v5.0.0")
+                    elif path == "/api/v2/torrents/info":
+                        self._respond(body=b"[]", content_type="application/json")
+                    elif path == "/api/v2/torrents/categories":
+                        body = json.dumps(CATEGORIES).encode()
+                        self._respond(body=body, content_type="application/json")
+                    elif path == "/api/v2/app/preferences":
+                        body = json.dumps({"save_path": "/tmp"}).encode()
+                        self._respond(body=body, content_type="application/json")
+                    else:
+                        self._respond()
+
+                def do_POST(self):
+                    content_length = int(self.headers.get("Content-Length", 0))
+                    body = self.rfile.read(content_length).decode()
+                    path = urlparse(self.path).path
+                    query = parse_qs(urlparse(self.path).query)
+                    form = parse_qs(body)
+                    params = {**query, **form}
+                    if path == "/api/v2/torrents/createCategory":
+                        name = params.get("category", [""])[0]
+                        save_path = params.get("savePath", params.get("save_path", [""]))[0] or "/downloads"
+                        if name:
+                            CATEGORIES[name] = {"name": name, "savePath": save_path}
+                    if path in ["/api/v2/torrents/editCategory", "/api/v2/torrents/removeCategory"]:
+                        self._respond()
+                        return
+                    self._respond()
+
+                def log_message(self, format, *args):
+                    pass
+
+
+            HTTPServer(("0.0.0.0", 6011), QBitMock).serve_forever()
+          '';
+        in
+        {
+          description = "Mock qBittorrent API";
+          wantedBy = [ "multi-user.target" ];
+          before = [
+            "sonarr-init.service"
+            "radarr-init.service"
+          ];
+          serviceConfig = {
+            ExecStart = "${pkgs.python3}/bin/python3 ${mockQbitScript}";
+            Type = "simple";
+          };
+        };
+
+      systemd.tmpfiles.rules = [
+        "d /media/tv 0755 sonarr sonarr -"
+        "d /media/movies 0755 radarr radarr -"
+      ];
+
+      services.sonarr = {
+        enable = true;
+        dataDir = "/var/lib/sonarr/.config/NzbDrone";
+        settings.server.port = lib.mkDefault 8989;
+      };
+
+      services.radarr = {
+        enable = true;
+        dataDir = "/var/lib/radarr/.config/Radarr";
+        settings.server.port = lib.mkDefault 7878;
+      };
+
+      services.prowlarr = {
+        enable = true;
+      };
+
+      services.arrInit.sonarr = {
+        enable = true;
+        serviceName = "sonarr";
+        dataDir = "/var/lib/sonarr/.config/NzbDrone";
+        port = 8989;
+        downloadClients = [
+          {
+            name = "qBittorrent";
+            implementation = "QBittorrent";
+            configContract = "QBittorrentSettings";
+            protocol = "torrent";
+            fields = {
+              host = "127.0.0.1";
+              port = 6011;
+              useSsl = false;
+              tvCategory = "tv";
+            };
+          }
+        ];
+        rootFolders = [ "/media/tv" ];
+      };
+
+      services.arrInit.radarr = {
+        enable = true;
+        serviceName = "radarr";
+        dataDir = "/var/lib/radarr/.config/Radarr";
+        port = 7878;
+        downloadClients = [
+          {
+            name = "qBittorrent";
+            implementation = "QBittorrent";
+            configContract = "QBittorrentSettings";
+            protocol = "torrent";
+            fields = {
+              host = "127.0.0.1";
+              port = 6011;
+              useSsl = false;
+              movieCategory = "movies";
+            };
+          }
+        ];
+        rootFolders = [ "/media/movies" ];
+      };
+
+      services.arrInit.prowlarr = {
+        enable = true;
+        serviceName = "prowlarr";
+        dataDir = "/var/lib/prowlarr";
+        port = 9696;
+        apiVersion = "v1";
+        syncedApps = [
+          {
+            name = "Sonarr";
+            implementation = "Sonarr";
+            configContract = "SonarrSettings";
+            prowlarrUrl = "http://localhost:9696";
+            baseUrl = "http://localhost:8989";
+            apiKeyFrom = "/var/lib/sonarr/.config/NzbDrone/config.xml";
+            syncCategories = [
+              5000
+              5010
+              5020
+              5030
+              5040
+              5045
+              5050
+              5090
+            ];
+            serviceName = "sonarr";
+          }
+          {
+            name = "Radarr";
+            implementation = "Radarr";
+            configContract = "RadarrSettings";
+            prowlarrUrl = "http://localhost:9696";
+            baseUrl = "http://localhost:7878";
+            apiKeyFrom = "/var/lib/radarr/.config/Radarr/config.xml";
+            syncCategories = [
+              2000
+              2010
+              2020
+              2030
+              2040
+              2045
+              2050
+              2060
+              2070
+              2080
+            ];
+            serviceName = "radarr";
+          }
+        ];
+      };
+    };
+
+  testScript = ''
+    start_all()
+
+    # Wait for services to start
+    machine.wait_for_unit("mock-qbittorrent.service")
+    machine.wait_until_succeeds("curl -sf http://localhost:6011/api/v2/app/version", timeout=30)
+    machine.wait_for_unit("sonarr.service")
+    machine.wait_for_unit("radarr.service")
+    machine.wait_for_unit("prowlarr.service")
+
+    # Wait for Sonarr API to be ready (config.xml is auto-generated on first start)
+    machine.wait_until_succeeds(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/sonarr/.config/NzbDrone/config.xml) && "
+        "curl -sf http://localhost:8989/api/v3/system/status -H \"X-Api-Key: $API_KEY\"",
+        timeout=120,
+    )
+
+    # Wait for Radarr API to be ready
+    machine.wait_until_succeeds(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/radarr/.config/Radarr/config.xml) && "
+        "curl -sf http://localhost:7878/api/v3/system/status -H \"X-Api-Key: $API_KEY\"",
+        timeout=120,
+    )
+
+    # Wait for Prowlarr API to be ready
+    machine.wait_until_succeeds(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/prowlarr/config.xml) && "
+        "curl -sf http://localhost:9696/api/v1/system/status -H \"X-Api-Key: $API_KEY\"",
+        timeout=180,
+    )
+
+    # Ensure init services run after config.xml exists
+    machine.succeed("systemctl restart sonarr-init.service")
+    machine.succeed("systemctl restart radarr-init.service")
+    machine.wait_for_unit("sonarr-init.service")
+    machine.wait_for_unit("radarr-init.service")
+
+    # Wait for init services to complete
+    machine.wait_for_unit("sonarr-init.service")
+    machine.wait_for_unit("radarr-init.service")
+
+    # Verify Sonarr download clients
+    machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/sonarr/.config/NzbDrone/config.xml) && "
+        "curl -sf http://localhost:8989/api/v3/downloadclient -H \"X-Api-Key: $API_KEY\" | "
+        "jq -e '.[] | select(.name == \"qBittorrent\")'"
+    )
+
+    # Verify Sonarr root folders
+    machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/sonarr/.config/NzbDrone/config.xml) && "
+        "curl -sf http://localhost:8989/api/v3/rootfolder -H \"X-Api-Key: $API_KEY\" | "
+        "jq -e '.[] | select(.path == \"/media/tv\")'"
+    )
+
+    # Verify Radarr download clients
+    machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/radarr/.config/Radarr/config.xml) && "
+        "curl -sf http://localhost:7878/api/v3/downloadclient -H \"X-Api-Key: $API_KEY\" | "
+        "jq -e '.[] | select(.name == \"qBittorrent\")'"
+    )
+
+    # Verify Radarr root folders
+    machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/radarr/.config/Radarr/config.xml) && "
+        "curl -sf http://localhost:7878/api/v3/rootfolder -H \"X-Api-Key: $API_KEY\" | "
+        "jq -e '.[] | select(.path == \"/media/movies\")'"
+    )
+
+    # Restart prowlarr-init now that all config.xml files exist
+    machine.succeed("systemctl restart prowlarr-init.service")
+    machine.wait_for_unit("prowlarr-init.service")
+
+    # Verify Sonarr registered as synced app in Prowlarr
+    machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/prowlarr/config.xml) && "
+        "curl -sf http://localhost:9696/api/v1/applications -H \"X-Api-Key: $API_KEY\" | "
+        "jq -e '.[] | select(.name == \"Sonarr\")'"
+    )
+
+    # Verify Radarr registered as synced app in Prowlarr
+    machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/prowlarr/config.xml) && "
+        "curl -sf http://localhost:9696/api/v1/applications -H \"X-Api-Key: $API_KEY\" | "
+        "jq -e '.[] | select(.name == \"Radarr\")'"
+    )
+
+    # Idempotency test: restart init services and verify no duplicate entries
+    machine.succeed("systemctl restart sonarr-init.service")
+    machine.succeed("systemctl restart radarr-init.service")
+    machine.succeed("systemctl restart prowlarr-init.service")
+
+    # Verify Sonarr still has exactly 1 download client
+    result = machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/sonarr/.config/NzbDrone/config.xml) && "
+        "curl -sf http://localhost:8989/api/v3/downloadclient -H \"X-Api-Key: $API_KEY\" | "
+        "jq '. | length'"
+    ).strip()
+    assert result == "1", f"Expected 1 Sonarr download client, got {result}"
+
+    # Verify Sonarr still has exactly 1 root folder
+    result = machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/sonarr/.config/NzbDrone/config.xml) && "
+        "curl -sf http://localhost:8989/api/v3/rootfolder -H \"X-Api-Key: $API_KEY\" | "
+        "jq '. | length'"
+    ).strip()
+    assert result == "1", f"Expected 1 Sonarr root folder, got {result}"
+
+    # Verify Radarr still has exactly 1 download client
+    result = machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/radarr/.config/Radarr/config.xml) && "
+        "curl -sf http://localhost:7878/api/v3/downloadclient -H \"X-Api-Key: $API_KEY\" | "
+        "jq '. | length'"
+    ).strip()
+    assert result == "1", f"Expected 1 Radarr download client, got {result}"
+
+    # Verify Radarr still has exactly 1 root folder
+    result = machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/radarr/.config/Radarr/config.xml) && "
+        "curl -sf http://localhost:7878/api/v3/rootfolder -H \"X-Api-Key: $API_KEY\" | "
+        "jq '. | length'"
+    ).strip()
+    assert result == "1", f"Expected 1 Radarr root folder, got {result}"
+
+    # Verify Prowlarr still has exactly 2 synced apps
+    result = machine.succeed(
+        "API_KEY=$(grep -oP '(?<=<ApiKey>)[^<]+' /var/lib/prowlarr/config.xml) && "
+        "curl -sf http://localhost:9696/api/v1/applications -H \"X-Api-Key: $API_KEY\" | "
+        "jq '. | length'"
+    ).strip()
+    assert result == "2", f"Expected 2 Prowlarr synced apps, got {result}"
+  '';
+}
diff --git a/tests/tests.nix b/tests/tests.nix
index f7a2e93..5b1e57b 100644
--- a/tests/tests.nix
+++ b/tests/tests.nix
@@ -21,4 +21,7 @@ in
   fail2banVaultwardenTest = handleTest ./fail2ban-vaultwarden.nix;
   fail2banImmichTest = handleTest ./fail2ban-immich.nix;
   fail2banJellyfinTest = handleTest ./fail2ban-jellyfin.nix;
+
+  # arr tests
+  arrInitTest = handleTest ./arr-init.nix;
 }