diff --git a/pgdog/src/config/mod.rs b/pgdog/src/config/mod.rs
index 6f9d794b..e156c9f3 100644
--- a/pgdog/src/config/mod.rs
+++ b/pgdog/src/config/mod.rs
@@ -352,6 +352,11 @@ pub struct General {
     /// Dry run for sharding. Parse the query, route to shard 0.
     #[serde(default)]
     pub dry_run: bool,
+    /// Require explicit shard selection for every query.
+    /// When enabled, queries without explicit shard selection will fail with an error.
+    /// This prevents unintended cross-shard queries in multi-tenant environments.
+    #[serde(default)]
+    pub require_shard_selection: bool,
     /// Idle timeout.
     #[serde(default = "General::idle_timeout")]
     pub idle_timeout: u64,
@@ -456,6 +461,7 @@ impl Default for General {
             query_timeout: Self::default_query_timeout(),
             checkout_timeout: Self::checkout_timeout(),
             dry_run: bool::default(),
+            require_shard_selection: bool::default(),
             idle_timeout: Self::idle_timeout(),
             client_idle_timeout: Self::default_client_idle_timeout(),
             mirror_queue: Self::mirror_queue(),
diff --git a/pgdog/src/frontend/router/parser/error.rs b/pgdog/src/frontend/router/parser/error.rs
index a1e26e73..8d3906ee 100644
--- a/pgdog/src/frontend/router/parser/error.rs
+++ b/pgdog/src/frontend/router/parser/error.rs
@@ -53,4 +53,7 @@ pub enum Error {
 
     #[error("missing parameter: ${0}")]
     MissingParameter(usize),
+
+    #[error("shard selection is required but not provided")]
+    ShardSelectionRequired,
 }
diff --git a/pgdog/src/frontend/router/parser/query.rs b/pgdog/src/frontend/router/parser/query.rs
index e5d19693..2ec89233 100644
--- a/pgdog/src/frontend/router/parser/query.rs
+++ b/pgdog/src/frontend/router/parser/query.rs
@@ -430,6 +430,15 @@ impl QueryParser {
 
         debug!("query router decision: {:#?}", command);
 
+        // Check if explicit shard selection is required
+        if config().config.general.require_shard_selection && shards > 1 {
+            if let Command::Query(ref route) = command {
+                if route.is_all_shards() {
+                    return Err(Error::ShardSelectionRequired);
+                }
+            }
+        }
+
         if dry_run {
             let default_route = Route::write(None);
             cache.record_command(
@@ -1454,4 +1463,58 @@ mod test {
 
         assert_eq!(route.shard(), &Shard::All);
     }
+
+    #[test]
+    fn test_require_shard_selection() {
+        // Save original config
+        let original_config = crate::config::config().clone();
+        
+        // Test that queries without shard selection fail when required
+        let mut config = crate::config::ConfigAndUsers::default();
+        config.config.general.require_shard_selection = true;
+        // Add multiple shards to trigger the requirement check
+        config.config.databases = vec![
+            crate::config::Database {
+                name: "test".to_string(),
+                shard: 0,
+                host: "localhost".to_string(),
+                ..Default::default()
+            },
+            crate::config::Database {
+                name: "test".to_string(),
+                shard: 1,
+                host: "localhost".to_string(),
+                ..Default::default()
+            },
+        ];
+        crate::config::set(config).unwrap();
+
+        // Test that a query without explicit shard selection fails
+        let query = "SELECT * FROM sharded WHERE value = 'test'";
+        let mut query_parser = QueryParser::default();
+        let buffer = Buffer::from(vec![Query::new(query).into()]);
+        let cluster = Cluster::new_test();
+        let mut stmt = PreparedStatements::default();
+        let params = Parameters::default();
+        let context = RouterContext::new(&buffer, &cluster, &mut stmt, &params, false).unwrap();
+        
+        let result = query_parser.parse(context);
+        assert!(matches!(result, Err(Error::ShardSelectionRequired)));
+
+        // Test that a query with explicit shard selection works
+        let query_with_shard = "/* pgdog_shard: 1 */ SELECT * FROM sharded WHERE value = 'test'";
+        let buffer_with_shard = Buffer::from(vec![Query::new(query_with_shard).into()]);
+        let context_with_shard = RouterContext::new(&buffer_with_shard, &cluster, &mut stmt, &params, false).unwrap();
+        
+        let mut query_parser2 = QueryParser::default();
+        let result_with_shard = query_parser2.parse(context_with_shard);
+        assert!(result_with_shard.is_ok());
+        
+        if let Ok(Command::Query(route)) = result_with_shard {
+            assert_eq!(route.shard(), &Shard::Direct(1));
+        }
+        
+        // Restore original config
+        crate::config::set((*original_config).clone()).unwrap();
+    }
 }