diff --git a/src/activitypub/deliverer.rs b/src/activitypub/deliverer.rs
index 9db2741..151a1c1 100644
--- a/src/activitypub/deliverer.rs
+++ b/src/activitypub/deliverer.rs
@@ -49,7 +49,8 @@ async fn send_activity(
         .header("Date", headers.date)
         .header("Digest", headers.digest.unwrap())
         .header("Signature", headers.signature)
-        .header("Content-Type", ACTIVITY_CONTENT_TYPE)
+        .header(reqwest::header::CONTENT_TYPE, ACTIVITY_CONTENT_TYPE)
+        .header(reqwest::header::USER_AGENT, instance.agent())
         .body(activity_json.to_owned());
 
     if instance.is_private {
diff --git a/src/activitypub/fetcher/fetchers.rs b/src/activitypub/fetcher/fetchers.rs
index 816340b..85ddf6c 100644
--- a/src/activitypub/fetcher/fetchers.rs
+++ b/src/activitypub/fetcher/fetchers.rs
@@ -59,6 +59,11 @@ async fn send_request(
             .header("Date", headers.date)
             .header("Signature", headers.signature);
     };
+    if !instance.is_private {
+        // Public instance should set User-Agent header
+        request_builder = request_builder
+            .header(reqwest::header::USER_AGENT, instance.agent());
+    };
 
     let data = request_builder
         .header(reqwest::header::ACCEPT, ACTIVITY_CONTENT_TYPE)
@@ -106,7 +111,13 @@ pub async fn fetch_profile(
     // TOOD: support http
     let webfinger_url = format!("https://{}/.well-known/webfinger", actor_host);
     let client = reqwest::Client::new();
-    let webfinger_data = client.get(&webfinger_url)
+    let mut request_builder = client.get(&webfinger_url);
+    if !instance.is_private {
+        // Public instance should set User-Agent header
+        request_builder = request_builder
+            .header(reqwest::header::USER_AGENT, instance.agent());
+    };
+    let webfinger_data = request_builder
         .query(&[("resource", webfinger_account_uri)])
         .send().await?
         .error_for_status()?
diff --git a/src/config.rs b/src/config.rs
index cdd3e79..7490a5f 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -144,6 +144,7 @@ impl Config {
     pub fn instance(&self) -> Instance {
         Instance {
             _url: self.try_instance_url().unwrap(),
+            _version: self.version.clone(),
             actor_key: self.try_instance_rsa_key().unwrap(),
             is_private: matches!(self.environment, Environment::Development),
         }
@@ -160,6 +161,7 @@ impl Config {
 
 pub struct Instance {
     _url: Url,
+    _version: String,
     // Instance actor
     pub actor_key: RsaPrivateKey,
     // Private instance won't send signed HTTP requests
@@ -183,6 +185,14 @@ impl Instance {
     pub fn actor_key_id(&self) -> String {
         format!("{}#main-key", self.actor_id())
     }
+
+    pub fn agent(&self) -> String {
+        format!(
+            "Mitra {version}; {instance_url}",
+            version=self._version,
+            instance_url=self.url(),
+        )
+    }
 }
 
 pub fn parse_config() -> Config {
@@ -225,12 +235,14 @@ mod tests {
         let instance_rsa_key = RsaPrivateKey::new(&mut OsRng, 512).unwrap();
         let instance = Instance {
             _url: instance_url,
+            _version: "1.0.0".to_string(),
             actor_key: instance_rsa_key,
             is_private: true,
         };
 
         assert_eq!(instance.url(), "https://example.com");
         assert_eq!(instance.host(), "example.com");
+        assert_eq!(instance.agent(), "Mitra 1.0.0; https://example.com");
     }
 
     #[test]
@@ -239,6 +251,7 @@ mod tests {
         let instance_rsa_key = RsaPrivateKey::new(&mut OsRng, 512).unwrap();
         let instance = Instance {
             _url: instance_url,
+            _version: "1.0.0".to_string(),
             actor_key: instance_rsa_key,
             is_private: true,
         };