diff --git a/client/client.go b/client/client.go
new file mode 100644
index 00000000..a670760b
--- /dev/null
+++ b/client/client.go
@@ -0,0 +1,135 @@
+package client
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	DefaultBaseURL = "https://ntfy.sh"
+)
+
+const (
+	MessageEvent   = "message"
+	KeepaliveEvent = "keepalive"
+	OpenEvent      = "open"
+)
+
+type Client struct {
+	BaseURL       string
+	Messages      chan *Message
+	subscriptions map[string]*subscription
+	mu            sync.Mutex
+}
+
+type Message struct {
+	ID       string
+	Event    string
+	Time     int64
+	Topic    string
+	Message  string
+	Title    string
+	Priority int
+	Tags     []string
+	BaseURL  string
+	TopicURL string
+	Raw      string
+}
+
+type subscription struct {
+	cancel context.CancelFunc
+}
+
+var DefaultClient = New()
+
+func New() *Client {
+	return &Client{
+		Messages:      make(chan *Message),
+		subscriptions: make(map[string]*subscription),
+	}
+}
+
+func (c *Client) Publish(topicURL, message string, options ...PublishOption) error {
+	req, _ := http.NewRequest("POST", topicURL, strings.NewReader(message))
+	for _, option := range options {
+		if err := option(req); err != nil {
+			return err
+		}
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("unexpected response %d from server", resp.StatusCode)
+	}
+	return err
+}
+
+func (c *Client) Subscribe(topicURL string) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if _, ok := c.subscriptions[topicURL]; ok {
+		return
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	c.subscriptions[topicURL] = &subscription{cancel}
+	go handleConnectionLoop(ctx, c.Messages, topicURL)
+}
+
+func (c *Client) Unsubscribe(topicURL string) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	sub, ok := c.subscriptions[topicURL]
+	if !ok {
+		return
+	}
+	sub.cancel()
+	return
+}
+
+func handleConnectionLoop(ctx context.Context, msgChan chan *Message, topicURL string) {
+	for {
+		if err := handleConnection(ctx, msgChan, topicURL); err != nil {
+			log.Printf("connection to %s failed: %s", topicURL, err.Error())
+		}
+		select {
+		case <-ctx.Done():
+			log.Printf("connection to %s exited", topicURL)
+			return
+		case <-time.After(5 * time.Second):
+		}
+	}
+}
+
+func handleConnection(ctx context.Context, msgChan chan *Message, topicURL string) error {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, fmt.Sprintf("%s/json", topicURL), nil)
+	if err != nil {
+		return err
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	scanner := bufio.NewScanner(resp.Body)
+	for scanner.Scan() {
+		var m *Message
+		line := scanner.Text()
+		if err := json.NewDecoder(strings.NewReader(line)).Decode(&m); err != nil {
+			return err
+		}
+		m.BaseURL = strings.TrimSuffix(topicURL, "/"+m.Topic) // FIXME hack!
+		m.TopicURL = topicURL
+		m.Raw = line
+		msgChan <- m
+	}
+	return nil
+}
diff --git a/client/options.go b/client/options.go
new file mode 100644
index 00000000..8812e4df
--- /dev/null
+++ b/client/options.go
@@ -0,0 +1,71 @@
+package client
+
+import (
+	"net/http"
+)
+
+type PublishOption func(r *http.Request) error
+
+func WithTitle(title string) PublishOption {
+	return func(r *http.Request) error {
+		if title != "" {
+			r.Header.Set("X-Title", title)
+		}
+		return nil
+	}
+}
+
+func WithPriority(priority string) PublishOption {
+	return func(r *http.Request) error {
+		if priority != "" {
+			r.Header.Set("X-Priority", priority)
+		}
+		return nil
+	}
+}
+
+func WithTags(tags string) PublishOption {
+	return func(r *http.Request) error {
+		if tags != "" {
+			r.Header.Set("X-Tags", tags)
+		}
+		return nil
+	}
+}
+
+func WithDelay(delay string) PublishOption {
+	return func(r *http.Request) error {
+		if delay != "" {
+			r.Header.Set("X-Delay", delay)
+		}
+		return nil
+	}
+}
+
+func WithNoCache() PublishOption {
+	return WithHeader("X-Cache", "no")
+}
+
+func WithNoFirebase() PublishOption {
+	return WithHeader("X-Firebase", "no")
+}
+
+func WithHeader(header, value string) PublishOption {
+	return func(r *http.Request) error {
+		r.Header.Set(header, value)
+		return nil
+	}
+}
+
+type SubscribeOption func(r *http.Request) error
+
+func WithSince(since string) PublishOption {
+	return func(r *http.Request) error {
+		if since != "" {
+			q := r.URL.Query()
+			q.Add("since", since)
+			r.URL.RawQuery = q.Encode()
+		}
+		return nil
+	}
+}
diff --git a/cmd/app.go b/cmd/app.go
index 379a58a0..e7234e01 100644
--- a/cmd/app.go
+++ b/cmd/app.go
@@ -2,112 +2,42 @@
 package cmd
 
 import (
-	"errors"
 	"fmt"
 	"github.com/urfave/cli/v2"
 	"github.com/urfave/cli/v2/altsrc"
-	"heckel.io/ntfy/config"
-	"heckel.io/ntfy/server"
+	"heckel.io/ntfy/client"
 	"heckel.io/ntfy/util"
 	"log"
 	"os"
-	"time"
+	"strings"
 )
 
 // New creates a new CLI application
 func New() *cli.App {
-	flags := []cli.Flag{
-		&cli.StringFlag{Name: "config", Aliases: []string{"c"}, EnvVars: []string{"NTFY_CONFIG_FILE"}, Value: "/etc/ntfy/config.yml", DefaultText: "/etc/ntfy/config.yml", Usage: "config file"},
-		altsrc.NewStringFlag(&cli.StringFlag{Name: "listen-http", Aliases: []string{"l"}, EnvVars: []string{"NTFY_LISTEN_HTTP"}, Value: config.DefaultListenHTTP, Usage: "ip:port used to as HTTP listen address"}),
-		altsrc.NewStringFlag(&cli.StringFlag{Name: "listen-https", Aliases: []string{"L"}, EnvVars: []string{"NTFY_LISTEN_HTTPS"}, Usage: "ip:port used to as HTTPS listen address"}),
-		altsrc.NewStringFlag(&cli.StringFlag{Name: "key-file", Aliases: []string{"K"}, EnvVars: []string{"NTFY_KEY_FILE"}, Usage: "private key file, if listen-https is set"}),
-		altsrc.NewStringFlag(&cli.StringFlag{Name: "cert-file", Aliases: []string{"E"}, EnvVars: []string{"NTFY_CERT_FILE"}, Usage: "certificate file, if listen-https is set"}),
-		altsrc.NewStringFlag(&cli.StringFlag{Name: "firebase-key-file", Aliases: []string{"F"}, EnvVars: []string{"NTFY_FIREBASE_KEY_FILE"}, Usage: "Firebase credentials file; if set additionally publish to FCM topic"}),
-		altsrc.NewStringFlag(&cli.StringFlag{Name: "cache-file", Aliases: []string{"C"}, EnvVars: []string{"NTFY_CACHE_FILE"}, Usage: "cache file used for message caching"}),
-		altsrc.NewDurationFlag(&cli.DurationFlag{Name: "cache-duration", Aliases: []string{"b"}, EnvVars: []string{"NTFY_CACHE_DURATION"}, Value: config.DefaultCacheDuration, Usage: "buffer messages for this time to allow `since` requests"}),
-		altsrc.NewDurationFlag(&cli.DurationFlag{Name: "keepalive-interval", Aliases: []string{"k"}, EnvVars: []string{"NTFY_KEEPALIVE_INTERVAL"}, Value: config.DefaultKeepaliveInterval, Usage: "interval of keepalive messages"}),
-		altsrc.NewDurationFlag(&cli.DurationFlag{Name: "manager-interval", Aliases: []string{"m"}, EnvVars: []string{"NTFY_MANAGER_INTERVAL"}, Value: config.DefaultManagerInterval, Usage: "interval of for message pruning and stats printing"}),
-		altsrc.NewIntFlag(&cli.IntFlag{Name: "global-topic-limit", Aliases: []string{"T"}, EnvVars: []string{"NTFY_GLOBAL_TOPIC_LIMIT"}, Value: config.DefaultGlobalTopicLimit, Usage: "total number of topics allowed"}),
-		altsrc.NewIntFlag(&cli.IntFlag{Name: "visitor-subscription-limit", Aliases: []string{"V"}, EnvVars: []string{"NTFY_VISITOR_SUBSCRIPTION_LIMIT"}, Value: config.DefaultVisitorSubscriptionLimit, Usage: "number of subscriptions per visitor"}),
-		altsrc.NewIntFlag(&cli.IntFlag{Name: "visitor-request-limit-burst", Aliases: []string{"B"}, EnvVars: []string{"NTFY_VISITOR_REQUEST_LIMIT_BURST"}, Value: config.DefaultVisitorRequestLimitBurst, Usage: "initial limit of requests per visitor"}),
-		altsrc.NewDurationFlag(&cli.DurationFlag{Name: "visitor-request-limit-replenish", Aliases: []string{"R"}, EnvVars: []string{"NTFY_VISITOR_REQUEST_LIMIT_REPLENISH"}, Value: config.DefaultVisitorRequestLimitReplenish, Usage: "interval at which burst limit is replenished (one per x)"}),
-		altsrc.NewBoolFlag(&cli.BoolFlag{Name: "behind-proxy", Aliases: []string{"P"}, EnvVars: []string{"NTFY_BEHIND_PROXY"}, Value: false, Usage: "if set, use X-Forwarded-For header to determine visitor IP address (for rate limiting)"}),
-	}
 	return &cli.App{
 		Name:                   "ntfy",
 		Usage:                  "Simple pub-sub notification service",
 		UsageText:              "ntfy [OPTION..]",
-		HideHelp:               true,
 		HideVersion:            true,
-		EnableBashCompletion:   true,
 		UseShortOptionHandling: true,
 		Reader:                 os.Stdin,
 		Writer:                 os.Stdout,
 		ErrWriter:              os.Stderr,
-		Action:                 execRun,
-		Before:                 initConfigFileInputSource("config", flags),
-		Flags:                  flags,
+		Action:                 execMainApp,
+		Before:                 initConfigFileInputSource("config", flagsServe), // DEPRECATED, see deprecation notice
+		Flags:                  flagsServe,                                      // DEPRECATED, see deprecation notice
+		Commands: []*cli.Command{
+			cmdServe,
+			cmdPublish,
+			cmdSubscribe,
+		},
 	}
 }
 
-func execRun(c *cli.Context) error {
-	// Read all the options
-	listenHTTP := c.String("listen-http")
-	listenHTTPS := c.String("listen-https")
-	keyFile := c.String("key-file")
-	certFile := c.String("cert-file")
-	firebaseKeyFile := c.String("firebase-key-file")
-	cacheFile := c.String("cache-file")
-	cacheDuration := c.Duration("cache-duration")
-	keepaliveInterval := c.Duration("keepalive-interval")
-	managerInterval := c.Duration("manager-interval")
-	globalTopicLimit := c.Int("global-topic-limit")
-	visitorSubscriptionLimit := c.Int("visitor-subscription-limit")
-	visitorRequestLimitBurst := c.Int("visitor-request-limit-burst")
-	visitorRequestLimitReplenish := c.Duration("visitor-request-limit-replenish")
-	behindProxy := c.Bool("behind-proxy")
-
-	// Check values
-	if firebaseKeyFile != "" && !util.FileExists(firebaseKeyFile) {
-		return errors.New("if set, FCM key file must exist")
-	} else if keepaliveInterval < 5*time.Second {
-		return errors.New("keepalive interval cannot be lower than five seconds")
-	} else if managerInterval < 5*time.Second {
-		return errors.New("manager interval cannot be lower than five seconds")
-	} else if cacheDuration > 0 && cacheDuration < managerInterval {
-		return errors.New("cache duration cannot be lower than manager interval")
-	} else if keyFile != "" && !util.FileExists(keyFile) {
-		return errors.New("if set, key file must exist")
-	} else if certFile != "" && !util.FileExists(certFile) {
-		return errors.New("if set, certificate file must exist")
-	} else if listenHTTPS != "" && (keyFile == "" || certFile == "") {
-		return errors.New("if listen-https is set, both key-file and cert-file must be set")
-	}
-
-	// Run server
-	conf := config.New(listenHTTP)
-	conf.ListenHTTPS = listenHTTPS
-	conf.KeyFile = keyFile
-	conf.CertFile = certFile
-	conf.FirebaseKeyFile = firebaseKeyFile
-	conf.CacheFile = cacheFile
-	conf.CacheDuration = cacheDuration
-	conf.KeepaliveInterval = keepaliveInterval
-	conf.ManagerInterval = managerInterval
-	conf.GlobalTopicLimit = globalTopicLimit
-	conf.VisitorSubscriptionLimit = visitorSubscriptionLimit
-	conf.VisitorRequestLimitBurst = visitorRequestLimitBurst
-	conf.VisitorRequestLimitReplenish = visitorRequestLimitReplenish
-	conf.BehindProxy = behindProxy
-	s, err := server.New(conf)
-	if err != nil {
-		log.Fatalln(err)
-	}
-	if err := s.Run(); err != nil {
-		log.Fatalln(err)
-	}
-	log.Printf("Exiting.")
-	return nil
+func execMainApp(c *cli.Context) error {
+	log.Printf("\x1b[1;33mDeprecation notice: Please run the server using 'ntfy serve'; see 'ntfy -h' for help.\x1b[0m")
+	log.Printf("\x1b[1;33mThis way of running the server will be removed Feb 2022.\x1b[0m")
+	return execServe(c)
 }
 
 // initConfigFileInputSource is like altsrc.InitInputSourceWithContext and altsrc.NewYamlSourceFromFlagFunc, but checks
@@ -127,3 +57,16 @@ func initConfigFileInputSource(configFlag string, flags []cli.Flag) cli.BeforeFu
 		return altsrc.ApplyInputSourceValues(context, inputSource, flags)
 	}
 }
+
+func expandTopicURL(s string) string {
+	if strings.HasPrefix(s, "http://") || strings.HasPrefix(s, "https://") {
+		return s
+	} else if strings.Contains(s, "/") {
+		return fmt.Sprintf("https://%s", s)
+	}
+	return fmt.Sprintf("%s/%s", client.DefaultBaseURL, s)
+}
+
+func collapseTopicURL(s string) string {
+	return strings.TrimPrefix(strings.TrimPrefix(s, "https://"), "http://")
+}
diff --git a/cmd/publish.go b/cmd/publish.go
new file mode 100644
index 00000000..274fee09
--- /dev/null
+++ b/cmd/publish.go
@@ -0,0 +1,70 @@
+package cmd
+
+import (
+	"errors"
+	"github.com/urfave/cli/v2"
+	"heckel.io/ntfy/client"
+	"strings"
+)
+
+var cmdPublish = &cli.Command{
+	Name:      "publish",
+	Aliases:   []string{"pub", "send"},
+	Usage:     "Send message via a ntfy server",
+	UsageText: "ntfy send [OPTIONS..] TOPIC MESSAGE",
+	Action:    execPublish,
+	Flags: []cli.Flag{
+		&cli.StringFlag{Name: "title", Aliases: []string{"t"}, Usage: "message title"},
+		&cli.StringFlag{Name: "priority", Aliases: []string{"p"}, Usage: "priority of the message (1=min, 2=low, 3=default, 4=high, 5=max)"},
+		&cli.StringFlag{Name: "tags", Aliases: []string{"ta"}, Usage: "comma separated list of tags and emojis"},
+		&cli.StringFlag{Name: "delay", Aliases: []string{"at", "in"}, Usage: "delay/schedule message"},
+		&cli.BoolFlag{Name: "no-cache", Aliases: []string{"C"}, Usage: "do not cache message server-side"},
+		&cli.BoolFlag{Name: "no-firebase", Aliases: []string{"F"}, Usage: "do not forward message to Firebase"},
+	},
+	Description: `Publish a message to a ntfy server.
+
+Examples:
+  ntfy publish mytopic This is my message                 # Send simple message
+  ntfy send myserver.com/mytopic "This is my message"     # Send message to different default host
+  ntfy pub -p high backups "Backups failed"               # Send high priority message
+  ntfy pub --tags=warning,skull backups "Backups failed"  # Add tags/emojis to message
+  ntfy pub --delay=10s delayed_topic Laterzz              # Delay message by 10s
+  ntfy pub --at=8:30am delayed_topic Laterzz              # Send message at 8:30am
+
+Please also check out the docs on publishing messages. Especially for the --tags and --delay options, 
+it has incredibly useful information: https://ntfy.sh/docs/publish/.`,
+}
+
+func execPublish(c *cli.Context) error {
+	if c.NArg() < 2 {
+		return errors.New("topic/message missing")
+	}
+	title := c.String("title")
+	priority := c.String("priority")
+	tags := c.String("tags")
+	delay := c.String("delay")
+	noCache := c.Bool("no-cache")
+	noFirebase := c.Bool("no-firebase")
+	topicURL := expandTopicURL(c.Args().Get(0))
+	message := strings.Join(c.Args().Slice()[1:], " ")
+	var options []client.PublishOption
+	if title != "" {
+		options = append(options, client.WithTitle(title))
+	}
+	if priority != "" {
+		options = append(options, client.WithPriority(priority))
+	}
+	if tags != "" {
+		options = append(options, client.WithTags(tags))
+	}
+	if delay != "" {
+		options = append(options, client.WithDelay(delay))
+	}
+	if noCache {
+		options = append(options, client.WithNoCache())
+	}
+	if noFirebase {
+		options = append(options, client.WithNoFirebase())
+	}
+	return client.DefaultClient.Publish(topicURL, message, options...)
+}
diff --git a/cmd/serve.go b/cmd/serve.go
new file mode 100644
index 00000000..2cdc8425
--- /dev/null
+++ b/cmd/serve.go
@@ -0,0 +1,108 @@
+// Package cmd provides the ntfy CLI application
+package cmd
+
+import (
+	"errors"
+	"github.com/urfave/cli/v2"
+	"github.com/urfave/cli/v2/altsrc"
+	"heckel.io/ntfy/config"
+	"heckel.io/ntfy/server"
+	"heckel.io/ntfy/util"
+	"log"
+	"time"
+)
+
+var flagsServe = []cli.Flag{
+	&cli.StringFlag{Name: "config", Aliases: []string{"c"}, EnvVars: []string{"NTFY_CONFIG_FILE"}, Value: "/etc/ntfy/config.yml", DefaultText: "/etc/ntfy/config.yml", Usage: "config file"},
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "listen-http", Aliases: []string{"l"}, EnvVars: []string{"NTFY_LISTEN_HTTP"}, Value: config.DefaultListenHTTP, Usage: "ip:port used to as HTTP listen address"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "listen-https", Aliases: []string{"L"}, EnvVars: []string{"NTFY_LISTEN_HTTPS"}, Usage: "ip:port used to as HTTPS listen address"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "key-file", Aliases: []string{"K"}, EnvVars: []string{"NTFY_KEY_FILE"}, Usage: "private key file, if listen-https is set"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "cert-file", Aliases: []string{"E"}, EnvVars: []string{"NTFY_CERT_FILE"}, Usage: "certificate file, if listen-https is set"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "firebase-key-file", Aliases: []string{"F"}, EnvVars: []string{"NTFY_FIREBASE_KEY_FILE"}, Usage: "Firebase credentials file; if set additionally publish to FCM topic"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "cache-file", Aliases: []string{"C"}, EnvVars: []string{"NTFY_CACHE_FILE"}, Usage: "cache file used for message caching"}),
+	altsrc.NewDurationFlag(&cli.DurationFlag{Name: "cache-duration", Aliases: []string{"b"}, EnvVars: []string{"NTFY_CACHE_DURATION"}, Value: config.DefaultCacheDuration, Usage: "buffer messages for this time to allow `since` requests"}),
+	altsrc.NewDurationFlag(&cli.DurationFlag{Name: "keepalive-interval", Aliases: []string{"k"}, EnvVars: []string{"NTFY_KEEPALIVE_INTERVAL"}, Value: config.DefaultKeepaliveInterval, Usage: "interval of keepalive messages"}),
+	altsrc.NewDurationFlag(&cli.DurationFlag{Name: "manager-interval", Aliases: []string{"m"}, EnvVars: []string{"NTFY_MANAGER_INTERVAL"}, Value: config.DefaultManagerInterval, Usage: "interval of for message pruning and stats printing"}),
+	altsrc.NewIntFlag(&cli.IntFlag{Name: "global-topic-limit", Aliases: []string{"T"}, EnvVars: []string{"NTFY_GLOBAL_TOPIC_LIMIT"}, Value: config.DefaultGlobalTopicLimit, Usage: "total number of topics allowed"}),
+	altsrc.NewIntFlag(&cli.IntFlag{Name: "visitor-subscription-limit", Aliases: []string{"V"}, EnvVars: []string{"NTFY_VISITOR_SUBSCRIPTION_LIMIT"}, Value: config.DefaultVisitorSubscriptionLimit, Usage: "number of subscriptions per visitor"}),
+	altsrc.NewIntFlag(&cli.IntFlag{Name: "visitor-request-limit-burst", Aliases: []string{"B"}, EnvVars: []string{"NTFY_VISITOR_REQUEST_LIMIT_BURST"}, Value: config.DefaultVisitorRequestLimitBurst, Usage: "initial limit of requests per visitor"}),
+	altsrc.NewDurationFlag(&cli.DurationFlag{Name: "visitor-request-limit-replenish", Aliases: []string{"R"}, EnvVars: []string{"NTFY_VISITOR_REQUEST_LIMIT_REPLENISH"}, Value: config.DefaultVisitorRequestLimitReplenish, Usage: "interval at which burst limit is replenished (one per x)"}),
+	altsrc.NewBoolFlag(&cli.BoolFlag{Name: "behind-proxy", Aliases: []string{"P"}, EnvVars: []string{"NTFY_BEHIND_PROXY"}, Value: false, Usage: "if set, use X-Forwarded-For header to determine visitor IP address (for rate limiting)"}),
+}
+
+var cmdServe = &cli.Command{
+	Name:      "serve",
+	Usage:     "Run the ntfy server",
+	UsageText: "ntfy serve [OPTIONS..]",
+	Action:    execServe,
+	Flags:     flagsServe,
+	Before:    initConfigFileInputSource("config", flagsServe),
+	Description: `Run the ntfy server and listen for incoming requests
+
+The command will load the configuration from /etc/ntfy/config.yml. Config options can 
+be overridden using the command line options.
+
+Examples:
+  ntfy serve                      # Starts server in the foreground (on port 80)
+  ntfy serve --listen-http :8080  # Starts server with alternate port`,
+}
+
+func execServe(c *cli.Context) error {
+	// Read all the options
+	listenHTTP := c.String("listen-http")
+	listenHTTPS := c.String("listen-https")
+	keyFile := c.String("key-file")
+	certFile := c.String("cert-file")
+	firebaseKeyFile := c.String("firebase-key-file")
+	cacheFile := c.String("cache-file")
+	cacheDuration := c.Duration("cache-duration")
+	keepaliveInterval := c.Duration("keepalive-interval")
+	managerInterval := c.Duration("manager-interval")
+	globalTopicLimit := c.Int("global-topic-limit")
+	visitorSubscriptionLimit := c.Int("visitor-subscription-limit")
+	visitorRequestLimitBurst := c.Int("visitor-request-limit-burst")
+	visitorRequestLimitReplenish := c.Duration("visitor-request-limit-replenish")
+	behindProxy := c.Bool("behind-proxy")
+
+	// Check values
+	if firebaseKeyFile != "" && !util.FileExists(firebaseKeyFile) {
+		return errors.New("if set, FCM key file must exist")
+	} else if keepaliveInterval < 5*time.Second {
+		return errors.New("keepalive interval cannot be lower than five seconds")
+	} else if managerInterval < 5*time.Second {
+		return errors.New("manager interval cannot be lower than five seconds")
+	} else if cacheDuration > 0 && cacheDuration < managerInterval {
+		return errors.New("cache duration cannot be lower than manager interval")
+	} else if keyFile != "" && !util.FileExists(keyFile) {
+		return errors.New("if set, key file must exist")
+	} else if certFile != "" && !util.FileExists(certFile) {
+		return errors.New("if set, certificate file must exist")
+	} else if listenHTTPS != "" && (keyFile == "" || certFile == "") {
+		return errors.New("if listen-https is set, both key-file and cert-file must be set")
+	}
+
+	// Run server
+	conf := config.New(listenHTTP)
+	conf.ListenHTTPS = listenHTTPS
+	conf.KeyFile = keyFile
+	conf.CertFile = certFile
+	conf.FirebaseKeyFile = firebaseKeyFile
+	conf.CacheFile = cacheFile
+	conf.CacheDuration = cacheDuration
+	conf.KeepaliveInterval = keepaliveInterval
+	conf.ManagerInterval = managerInterval
+	conf.GlobalTopicLimit = globalTopicLimit
+	conf.VisitorSubscriptionLimit = visitorSubscriptionLimit
+	conf.VisitorRequestLimitBurst = visitorRequestLimitBurst
+	conf.VisitorRequestLimitReplenish = visitorRequestLimitReplenish
+	conf.BehindProxy = behindProxy
+	s, err := server.New(conf)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	if err := s.Run(); err != nil {
+		log.Fatalln(err)
+	}
+	log.Printf("Exiting.")
+	return nil
+}
diff --git a/cmd/subscribe.go b/cmd/subscribe.go
new file mode 100644
index 00000000..0b03b69d
--- /dev/null
+++ b/cmd/subscribe.go
@@ -0,0 +1,132 @@
+package cmd
+
+import (
+	"errors"
+	"fmt"
+	"github.com/urfave/cli/v2"
+	"heckel.io/ntfy/client"
+	"heckel.io/ntfy/util"
+	"log"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+var cmdSubscribe = &cli.Command{
+	Name:      "subscribe",
+	Aliases:   []string{"sub"},
+	Usage:     "Subscribe to one or more topics on a ntfy server",
+	UsageText: "ntfy subscribe [OPTIONS..] TOPIC",
+	Action:    execSubscribe,
+	Flags: []cli.Flag{
+		&cli.StringFlag{Name: "exec", Aliases: []string{"e"}, Usage: "execute command for each message event"},
+		&cli.StringFlag{Name: "since", Aliases: []string{"s"}, Usage: "return events since (Unix timestamp, or all)"},
+	},
+	Description: `(THIS COMMAND IS INCUBATING. IT MAY CHANGE WITHOUT NOTICE.)
+
+Subscribe to one or more topics on a ntfy server, and either print 
+or execute commands for every arriving message. 
+
+By default, the subscribe command just prints the JSON representation of a message. 
+When --exec is passed, each incoming message will execute a command. The message fields 
+are passed to the command as environment variables:
+
+    Variable        Aliases         Description
+    --------------- --------------- -----------------------------------
+    $NTFY_MESSAGE   $message, $m    Message body
+    $NTFY_TITLE     $title, $t      Message title
+    $NTFY_PRIORITY  $priority, $p   Message priority (1=min, 5=max)
+    $NTFY_TAGS      $tags, $ta      Message tags (comma separated list)
+    $NTFY_ID        $id             Unique message ID
+    $NTFY_TIME      $time           Unix timestamp of the message delivery
+    $NTFY_TOPIC     $topic          Topic name
+    $NTFY_EVENT     $event, $ev     Event identifier (always "message")
+
+Examples:
+  ntfy subscribe mytopic                       # Prints JSON for incoming messages to stdout
+  ntfy sub home.lan/backups alerts             # Subscribe to two different topics
+  ntfy sub --exec='notify-send "$m"' mytopic   # Execute command for incoming messages'  
+`,
+}
+
+func execSubscribe(c *cli.Context) error {
+	if c.NArg() < 1 {
+		return errors.New("topic missing")
+	}
+	log.Printf("\x1b[1;33mThis command is incubating. The interface may change without notice.\x1b[0m")
+	cl := client.DefaultClient
+	command := c.String("exec")
+	for _, topic := range c.Args().Slice() {
+		cl.Subscribe(expandTopicURL(topic))
+	}
+	for m := range cl.Messages {
+		_ = dispatchMessage(c, command, m)
+	}
+	return nil
+}
+
+func dispatchMessage(c *cli.Context, command string, m *client.Message) error {
+	if command != "" {
+		return execCommand(c, command, m)
+	}
+	fmt.Println(m.Raw)
+	return nil
+}
+
+func execCommand(c *cli.Context, command string, m *client.Message) error {
+	if m.Event == client.OpenEvent {
+		log.Printf("[%s] Connection opened, subscribed to topic", collapseTopicURL(m.TopicURL))
+	} else if m.Event == client.MessageEvent {
+		go func() {
+			if err := runCommandInternal(c, command, m); err != nil {
+				log.Printf("[%s] Command failed: %s", collapseTopicURL(m.TopicURL), err.Error())
+			}
+		}()
+	}
+	return nil
+}
+
+func runCommandInternal(c *cli.Context, command string, m *client.Message) error {
+	scriptFile, err := createTmpScript(command)
+	if err != nil {
+		return err
+	}
+	defer os.Remove(scriptFile)
+	log.Printf("[%s] Executing: %s (for message: %s)", collapseTopicURL(m.TopicURL), command, m.Raw)
+	cmd := exec.Command("sh", "-c", scriptFile)
+	cmd.Stdin = c.App.Reader
+	cmd.Stdout = c.App.Writer
+	cmd.Stderr = c.App.ErrWriter
+	cmd.Env = envVars(m)
+	return cmd.Run()
+}
+
+func createTmpScript(command string) (string, error) {
+	scriptFile := fmt.Sprintf("%s/ntfy-subscribe-%s.sh.tmp", os.TempDir(), util.RandomString(10))
+	script := fmt.Sprintf("#!/bin/sh\n%s", command)
+	if err := os.WriteFile(scriptFile, []byte(script), 0700); err != nil {
+		return "", err
+	}
+	return scriptFile, nil
+}
+
+func envVars(m *client.Message) []string {
+	env := os.Environ()
+	env = append(env, envVar(m.ID, "NTFY_ID", "id")...)
+	env = append(env, envVar(m.Event, "NTFY_EVENT", "event", "ev")...)
+	env = append(env, envVar(m.Topic, "NTFY_TOPIC", "topic")...)
+	env = append(env, envVar(fmt.Sprintf("%d", m.Time), "NTFY_TIME", "time")...)
+	env = append(env, envVar(m.Message, "NTFY_MESSAGE", "message", "m")...)
+	env = append(env, envVar(m.Title, "NTFY_TITLE", "title", "t")...)
+	env = append(env, envVar(fmt.Sprintf("%d", m.Priority), "NTFY_PRIORITY", "priority", "prio", "p")...)
+	env = append(env, envVar(strings.Join(m.Tags, ","), "NTFY_TAGS", "tags", "ta")...)
+	return env
+}
+
+func envVar(value string, vars ...string) []string {
+	env := make([]string, 0)
+	for _, v := range vars {
+		env = append(env, fmt.Sprintf("%s=%s", v, value))
+	}
+	return env
+}
diff --git a/config/ntfy.service b/config/ntfy.service
index 77899517..6645b21f 100644
--- a/config/ntfy.service
+++ b/config/ntfy.service
@@ -5,7 +5,7 @@ After=network.target
 [Service]
 User=ntfy
 Group=ntfy
-ExecStart=/usr/bin/ntfy
+ExecStart=/usr/bin/ntfy serve
 Restart=on-failure
 AmbientCapabilities=CAP_NET_BIND_SERVICE
 LimitNOFILE=10000
diff --git a/main.go b/main.go
index cecae09d..f6cdbdce 100644
--- a/main.go
+++ b/main.go
@@ -19,7 +19,7 @@ func main() {
 Try 'ntfy COMMAND --help' for more information.
 
 ntfy %s (%s), runtime %s, built at %s
-Copyright (C) 2021 Philipp C. Heckel, distributed under the Apache License 2.0
+Copyright (C) 2021 Philipp C. Heckel, licensed under Apache License 2.0 & GPLv2
 `, version, commit[:7], runtime.Version(), date)
 
 	app := cmd.New()
diff --git a/server/server.go b/server/server.go
index 1cb6edad..30342098 100644
--- a/server/server.go
+++ b/server/server.go
@@ -328,22 +328,9 @@ func (s *Server) parseParams(r *http.Request, m *message) (cache bool, firebase
 	if messageStr != "" {
 		m.Message = messageStr
 	}
-	priorityStr := readParam(r, "x-priority", "priority", "prio", "p")
-	if priorityStr != "" {
-		switch strings.ToLower(priorityStr) {
-		case "1", "min":
-			m.Priority = 1
-		case "2", "low":
-			m.Priority = 2
-		case "3", "default":
-			m.Priority = 3
-		case "4", "high":
-			m.Priority = 4
-		case "5", "max", "urgent":
-			m.Priority = 5
-		default:
-			return false, false, errHTTPBadRequest
-		}
+	m.Priority, err = util.ParsePriority(readParam(r, "x-priority", "priority", "prio", "p"))
+	if err != nil {
+		return false, false, errHTTPBadRequest
 	}
 	tagsStr := readParam(r, "x-tags", "tag", "tags", "ta")
 	if tagsStr != "" {
diff --git a/util/util.go b/util/util.go
index 331f8c5e..665166df 100644
--- a/util/util.go
+++ b/util/util.go
@@ -1,9 +1,11 @@
 package util
 
 import (
+	"errors"
 	"fmt"
 	"math/rand"
 	"os"
+	"strings"
 	"sync"
 	"time"
 )
@@ -15,6 +17,8 @@ const (
 var (
 	random      = rand.New(rand.NewSource(time.Now().UnixNano()))
 	randomMutex = sync.Mutex{}
+
+	errInvalidPriority = errors.New("unknown priority")
 )
 
 // FileExists checks if a file exists, and returns true if it does
@@ -75,3 +79,22 @@ func DurationToHuman(d time.Duration) (str string) {
 	}
 	return
 }
+
+func ParsePriority(priority string) (int, error) {
+	switch strings.ToLower(priority) {
+	case "":
+		return 0, nil
+	case "1", "min":
+		return 1, nil
+	case "2", "low":
+		return 2, nil
+	case "3", "default":
+		return 3, nil
+	case "4", "high":
+		return 4, nil
+	case "5", "max", "urgent":
+		return 5, nil
+	default:
+		return 0, errInvalidPriority
+	}
+}