diff --git a/Cargo.toml b/Cargo.toml
index 692fd60f..9b6e6f0a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -50,6 +50,7 @@ rest_pat_in_fully_bound_structs = "warn"
 same_name_method = "warn"
 semicolon_inside_block = "warn"
 str_to_string = "warn"
+string_add = "warn"
 string_lit_chars_any = "warn"
 string_to_string = "warn"
 suspicious_xor_used_as_pow = "warn"
diff --git a/src/api/appservice_server.rs b/src/api/appservice_server.rs
index 3ec7a66e..0c29472d 100644
--- a/src/api/appservice_server.rs
+++ b/src/api/appservice_server.rs
@@ -44,7 +44,7 @@ where
     };
 
     parts.path_and_query = Some(
-        (old_path_and_query + symbol + "access_token=" + hs_token)
+        format!("{old_path_and_query}{symbol}access_token={hs_token}")
             .parse()
             .unwrap(),
     );
diff --git a/src/api/client_server/media.rs b/src/api/client_server/media.rs
index 62fe4c09..493c31da 100644
--- a/src/api/client_server/media.rs
+++ b/src/api/client_server/media.rs
@@ -43,7 +43,7 @@ pub(crate) async fn create_content_route(
             mxc.clone(),
             body.filename
                 .as_ref()
-                .map(|filename| "inline; filename=".to_owned() + filename)
+                .map(|filename| format!("inline; filename={filename}"))
                 .as_deref(),
             body.content_type.as_deref(),
             &body.file,
diff --git a/src/api/client_server/sync.rs b/src/api/client_server/sync.rs
index f174e98b..a7167d26 100644
--- a/src/api/client_server/sync.rs
+++ b/src/api/client_server/sync.rs
@@ -1598,15 +1598,15 @@ pub(crate) async fn sync_events_v4_route(
         let name = match &*heroes {
             [] => None,
             [only] => Some(only.0.clone()),
-            [firsts @ .., last] => Some(
-                firsts
+            [firsts @ .., last] => Some({
+                let firsts = firsts
                     .iter()
                     .map(|h| h.0.clone())
                     .collect::<Vec<_>>()
-                    .join(", ")
-                    + " and "
-                    + &last.0,
-            ),
+                    .join(", ");
+
+                format!("{firsts} and {}", last.0)
+            }),
         };
 
         let avatar = if let [only] = &*heroes {
diff --git a/src/service/admin.rs b/src/service/admin.rs
index d8c3a29b..fd954bb3 100644
--- a/src/service/admin.rs
+++ b/src/service/admin.rs
@@ -385,17 +385,17 @@ impl Service {
                 let output = format!(
                     "Rooms:\n{}",
                     room_ids
-                        .filter_map(|r| r.ok())
-                        .map(|id| id.to_string()
-                            + "\tMembers: "
-                            + &services()
+                        .filter_map(std::result::Result::ok)
+                        .map(|id| format!(
+                            "{id}\tMembers: {}",
+                            &services()
                                 .rooms
                                 .state_cache
                                 .room_joined_count(&id)
                                 .ok()
                                 .flatten()
                                 .unwrap_or(0)
-                                .to_string())
+                        ))
                         .collect::<Vec<_>>()
                         .join("\n")
                 );