diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 00000000..81e82cc0
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,5 @@
+{
+  "cSpell.words": [
+    "smstring"
+  ]
+}
diff --git a/crates/loro-core/Cargo.toml b/crates/loro-core/Cargo.toml
index 8c30f7ac..1544cbf0 100644
--- a/crates/loro-core/Cargo.toml
+++ b/crates/loro-core/Cargo.toml
@@ -14,6 +14,8 @@ fxhash = "0.2.1"
 ring = "0.16.20"
 moveit = "0.5.0"
 pin-project = "1.0.10"
+serde = {version = "1.0.140", features = ["derive"]}
+thiserror = "1.0.31"
 
 [dev-dependencies]
 proptest = "1.0.0"
diff --git a/crates/loro-core/src/container.rs b/crates/loro-core/src/container.rs
index a754bceb..a358f3c3 100644
--- a/crates/loro-core/src/container.rs
+++ b/crates/loro-core/src/container.rs
@@ -5,10 +5,11 @@
 //! Every [Container] can take a [Snapshot], which contains [crate::LoroValue] that describes the state.
 //!
 use crate::{
-    op::OpProxy, snapshot::Snapshot, version::VersionVector, InsertContent, InternalString,
-    LogStore, Op, SmString, ID,
+    op::OpProxy, version::VersionVector, InsertContent, InternalString, LogStore, LoroValue, Op,
+    SmString, ID,
 };
 use rle::{HasLength, Mergable, Sliceable};
+use serde::Serialize;
 use std::{
     alloc::Layout,
     any::{self, Any, TypeId},
@@ -26,10 +27,12 @@ pub use manager::*;
 
 pub trait Container: Debug + Any + Unpin {
     fn id(&self) -> &ContainerID;
-    fn container_type(&self) -> ContainerType;
+    fn type_(&self) -> ContainerType;
     fn apply(&mut self, op: &OpProxy);
-    fn snapshot(&mut self) -> Snapshot;
-    fn checkout_version(&mut self, vv: &VersionVector, log: &LogStore);
+    fn checkout_version(&mut self, vv: &VersionVector);
+    fn get_value(&mut self) -> &LoroValue;
+    // TODO: need a custom serializer
+    // fn serialize(&self) -> Vec<u8>;
 }
 
 pub(crate) trait Cast<T> {
@@ -49,7 +52,7 @@ impl<T: Any> Cast<T> for dyn Container {
     }
 }
 
-#[derive(Hash, PartialEq, Eq, Debug, Clone)]
+#[derive(Hash, PartialEq, Eq, Debug, Clone, Serialize)]
 pub enum ContainerID {
     /// Root container does not need a insert op to create. It can be created implicitly.
     Root {
diff --git a/crates/loro-core/src/container/container_content.rs b/crates/loro-core/src/container/container_content.rs
index 788734a2..d3444f5f 100644
--- a/crates/loro-core/src/container/container_content.rs
+++ b/crates/loro-core/src/container/container_content.rs
@@ -1,11 +1,12 @@
-use crate::{InsertContent, SmString, ID};
+use crate::{smstring::SmString, InsertContent, ID};
 use rle::{HasLength, Mergable, Sliceable};
+use serde::Serialize;
 use std::alloc::Layout;
 
 #[derive(Debug, Clone)]
 pub(crate) enum Slot {}
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize)]
 pub enum ContainerType {
     /// See [`crate::text::TextContent`]
     Text,
diff --git a/crates/loro-core/src/container/map/map_container.rs b/crates/loro-core/src/container/map/map_container.rs
index 768b1f21..752be688 100644
--- a/crates/loro-core/src/container/map/map_container.rs
+++ b/crates/loro-core/src/container/map/map_container.rs
@@ -1,15 +1,16 @@
 use std::{pin::Pin, ptr::NonNull, rc::Weak};
 
 use fxhash::FxHashMap;
+use serde::Serialize;
 
 use crate::{
     container::{Container, ContainerID, ContainerType},
-    id::ID,
+    id::{Counter, ID},
     op::{utils::downcast_ref, Op},
     op::{OpContent, OpProxy},
     value::{InsertValue, LoroValue},
     version::TotalOrderStamp,
-    ClientID, InternalString, Lamport, LogStore, OpType, Snapshot,
+    ClientID, InternalString, Lamport, LogStore, OpType,
 };
 
 use super::MapInsertContent;
@@ -22,12 +23,14 @@ pub struct MapContainer {
     id: ContainerID,
     state: FxHashMap<InternalString, ValueSlot>,
     log_store: NonNull<LogStore>,
+    value: Option<LoroValue>,
 }
 
 #[derive(Debug)]
 struct ValueSlot {
     value: InsertValue,
     order: TotalOrderStamp,
+    counter: Counter,
 }
 
 impl MapContainer {
@@ -37,6 +40,7 @@ impl MapContainer {
             id,
             state: FxHashMap::default(),
             log_store: store,
+            value: None,
         }
     }
 
@@ -53,8 +57,10 @@ impl MapContainer {
             lamport: store.next_lamport(),
         };
 
+        let id = store.next_id(client_id);
+        let counter = id.counter;
         store.append_local_ops(vec![Op {
-            id: store.next_id(client_id),
+            id,
             content: OpContent::Normal {
                 container: self_id,
                 content: Box::new(MapInsertContent {
@@ -64,7 +70,14 @@ impl MapContainer {
             },
         }]);
 
-        self.state.insert(key, ValueSlot { value, order });
+        self.state.insert(
+            key,
+            ValueSlot {
+                value,
+                order,
+                counter,
+            },
+        );
     }
 
     #[inline]
@@ -79,7 +92,7 @@ impl Container for MapContainer {
         &self.id
     }
 
-    fn container_type(&self) -> ContainerType {
+    fn type_(&self) -> ContainerType {
         ContainerType::Map
     }
 
@@ -104,6 +117,7 @@ impl Container for MapContainer {
                         ValueSlot {
                             value: v.value.clone(),
                             order,
+                            counter: op.id().counter,
                         },
                     );
                 }
@@ -112,16 +126,19 @@ impl Container for MapContainer {
         }
     }
 
-    fn snapshot(&mut self) -> Snapshot {
-        let mut map = FxHashMap::default();
-        for (key, value) in self.state.iter() {
-            map.insert(key.clone(), value.value.clone().into());
+    fn get_value(&mut self) -> &LoroValue {
+        if self.value.is_none() {
+            let mut map = FxHashMap::default();
+            for (key, value) in self.state.iter() {
+                map.insert(key.clone(), value.value.clone().into());
+            }
+            self.value = Some(LoroValue::Map(map));
         }
 
-        Snapshot::new(LoroValue::Map(map))
+        self.value.as_ref().unwrap()
     }
 
-    fn checkout_version(&mut self, _vv: &crate::version::VersionVector, _log: &crate::LogStore) {
+    fn checkout_version(&mut self, vv: &crate::version::VersionVector) {
         todo!()
     }
 }
diff --git a/crates/loro-core/src/container/map/map_content.rs b/crates/loro-core/src/container/map/map_content.rs
index 46c46b73..5d038aec 100644
--- a/crates/loro-core/src/container/map/map_content.rs
+++ b/crates/loro-core/src/container/map/map_content.rs
@@ -1,6 +1,6 @@
 use rle::{HasLength, Mergable, Sliceable};
 
-use crate::{value::InsertValue, ContentType, InsertContent, InternalString};
+use crate::{id::ID, value::InsertValue, ContentType, InsertContent, InternalString};
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct MapInsertContent {
diff --git a/crates/loro-core/src/container/map/tests.rs b/crates/loro-core/src/container/map/tests.rs
index fe408baf..10572950 100644
--- a/crates/loro-core/src/container/map/tests.rs
+++ b/crates/loro-core/src/container/map/tests.rs
@@ -28,7 +28,7 @@ fn basic() {
         "haha".into() => LoroValue::Integer(1)
     );
 
-    assert_eq!(*container.snapshot().value(), LoroValue::Map(ans));
+    assert_eq!(*container.get_value(), LoroValue::Map(ans));
 }
 
 #[cfg(not(no_proptest))]
@@ -47,9 +47,8 @@ mod map_proptest {
             for (k, v) in key.iter().zip(value.iter()) {
                 map.insert(k.clone(), v.clone());
                 container.insert(k.clone().into(), v.clone());
-                let snapshot = container.snapshot();
-                let snapshot = snapshot.value().to_map().unwrap();
-                for (key, value) in snapshot.iter() {
+                let snapshot = container.get_value();
+                for (key, value) in snapshot.to_map().unwrap().iter() {
                     assert_eq!(map.get(&key.to_string()).map(|x|x.clone().into()), Some(value.clone()));
                 }
             }
diff --git a/crates/loro-core/src/error.rs b/crates/loro-core/src/error.rs
new file mode 100644
index 00000000..58eaacd9
--- /dev/null
+++ b/crates/loro-core/src/error.rs
@@ -0,0 +1,11 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum LoroError {
+    // #[error("the data for key `{0}` is not available")]
+    // Redaction(String),
+    // #[error("invalid header (expected {expected:?}, found {found:?})")]
+    // InvalidHeader { expected: String, found: String },
+    // #[error("unknown data store error")]
+    // Unknown,
+}
diff --git a/crates/loro-core/src/id.rs b/crates/loro-core/src/id.rs
index a680780d..f2d446e7 100644
--- a/crates/loro-core/src/id.rs
+++ b/crates/loro-core/src/id.rs
@@ -1,7 +1,9 @@
+use serde::Serialize;
+
 pub type ClientID = u64;
 pub type Counter = u32;
 
-#[derive(PartialEq, Eq, Hash, Clone, Debug, Copy, PartialOrd, Ord)]
+#[derive(PartialEq, Eq, Hash, Clone, Debug, Copy, PartialOrd, Ord, Serialize)]
 pub struct ID {
     pub client_id: u64,
     pub counter: u32,
diff --git a/crates/loro-core/src/lib.rs b/crates/loro-core/src/lib.rs
index d324a1d6..a8ff0038 100644
--- a/crates/loro-core/src/lib.rs
+++ b/crates/loro-core/src/lib.rs
@@ -10,9 +10,11 @@ pub mod id;
 pub mod op;
 pub mod version;
 
+mod error;
 mod id_span;
 mod log_store;
 mod loro;
+mod smstring;
 mod snapshot;
 mod tests;
 mod value;
@@ -20,9 +22,8 @@ mod value;
 pub(crate) mod macros;
 pub(crate) use change::{Change, Lamport, Timestamp};
 pub(crate) use id::{ClientID, ID};
-pub(crate) use snapshot::Snapshot;
-pub(crate) type SmString = SmartString<LazyCompact>;
 pub(crate) use op::{ContentType, InsertContent, Op, OpContent, OpType};
+pub(crate) use smstring::SmString;
 pub(crate) type InternalString = DefaultAtom;
 
 pub use container::ContainerType;
@@ -30,5 +31,4 @@ pub use log_store::LogStore;
 pub use loro::*;
 pub use value::LoroValue;
 
-use smartstring::{LazyCompact, SmartString};
 use string_cache::DefaultAtom;
diff --git a/crates/loro-core/src/smstring.rs b/crates/loro-core/src/smstring.rs
new file mode 100644
index 00000000..d2563cd8
--- /dev/null
+++ b/crates/loro-core/src/smstring.rs
@@ -0,0 +1,46 @@
+use std::ops::DerefMut;
+
+use std::ops::Deref;
+
+use serde::Serialize;
+use smartstring::LazyCompact;
+
+use smartstring::SmartString;
+
+#[repr(transparent)]
+#[derive(Debug, PartialEq, PartialOrd, Ord, Eq, Clone)]
+pub struct SmString(pub(crate) SmartString<LazyCompact>);
+
+impl Deref for SmString {
+    type Target = SmartString<LazyCompact>;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for SmString {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl From<SmartString<LazyCompact>> for SmString {
+    fn from(s: SmartString<LazyCompact>) -> Self {
+        SmString(s)
+    }
+}
+
+impl From<String> for SmString {
+    fn from(s: String) -> Self {
+        SmString(s.into())
+    }
+}
+
+impl Serialize for SmString {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serializer.serialize_str(&self.0)
+    }
+}
diff --git a/crates/loro-core/src/snapshot.rs b/crates/loro-core/src/snapshot.rs
index 07cec75b..8b137891 100644
--- a/crates/loro-core/src/snapshot.rs
+++ b/crates/loro-core/src/snapshot.rs
@@ -1,16 +1 @@
-use crate::value::LoroValue;
 
-#[derive(Debug, PartialEq, Clone)]
-pub struct Snapshot {
-    value: LoroValue,
-}
-
-impl Snapshot {
-    pub fn new(value: LoroValue) -> Self {
-        Snapshot { value }
-    }
-
-    pub fn value(&self) -> &LoroValue {
-        &self.value
-    }
-}
diff --git a/crates/loro-core/src/value.rs b/crates/loro-core/src/value.rs
index 975c1da2..a1af55b9 100644
--- a/crates/loro-core/src/value.rs
+++ b/crates/loro-core/src/value.rs
@@ -1,9 +1,9 @@
 use fxhash::FxHashMap;
 
-use crate::{container::ContainerID, InternalString, SmString};
+use crate::{container::ContainerID, smstring::SmString, InternalString};
 
 /// [LoroValue] is used to represents the state of CRDT at a given version
-#[derive(Debug, PartialEq, Clone)]
+#[derive(Debug, PartialEq, Clone, serde::Serialize)]
 pub enum LoroValue {
     Null,
     Bool(bool),
diff --git a/justfile b/justfile
index 73087815..164a1fb4 100644
--- a/justfile
+++ b/justfile
@@ -7,3 +7,12 @@ test:
 # test without proptest
 test-fast:
   RUSTFLAGS='--cfg no_proptest' cargo nextest run
+
+check-unsafe:
+  env RUSTFLAGS="-Funsafe-code --cap-lints=warn" cargo check
+
+deny:
+  cargo deny check
+
+crev:
+  cargo crev crate check