diff --git a/cmd/mstdn/main.go b/cmd/mstdn/main.go
index f17e27a..4386768 100644
--- a/cmd/mstdn/main.go
+++ b/cmd/mstdn/main.go
@@ -370,6 +370,7 @@ func run() int {
 		}
 
 		client := mastodon.NewClient(config)
+		client.UserAgent = "mstdn"
 		app.Metadata = map[string]interface{}{
 			"client":      client,
 			"config":      config,
diff --git a/mastodon.go b/mastodon.go
index d2f6182..d0a94d4 100644
--- a/mastodon.go
+++ b/mastodon.go
@@ -31,7 +31,8 @@ type Config struct {
 // Client is a API client for mastodon.
 type Client struct {
 	http.Client
-	config *Config
+	config    *Config
+	UserAgent string
 }
 
 func (c *Client) doAPI(ctx context.Context, method string, uri string, params interface{}, res interface{}, pg *Pagination) error {
@@ -117,6 +118,9 @@ func (c *Client) doAPI(ctx context.Context, method string, uri string, params in
 	if params != nil {
 		req.Header.Set("Content-Type", ct)
 	}
+	if c.UserAgent != "" {
+		req.Header.Set("User-Agent", c.UserAgent)
+	}
 
 	var resp *http.Response
 	backoff := 1000 * time.Millisecond
@@ -211,6 +215,9 @@ func (c *Client) authenticate(ctx context.Context, params url.Values) error {
 	}
 	req = req.WithContext(ctx)
 	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	if c.UserAgent != "" {
+		req.Header.Set("User-Agent", c.UserAgent)
+	}
 	resp, err := c.Do(req)
 	if err != nil {
 		return err