diff --git a/core/lib/types/src/api/mod.rs b/core/lib/types/src/api/mod.rs
index 26a6230be613..2aa5d55529e8 100644
--- a/core/lib/types/src/api/mod.rs
+++ b/core/lib/types/src/api/mod.rs
@@ -600,7 +600,7 @@ pub struct GetLogsFilter {
 #[derive(Debug, Serialize, Deserialize, Clone)]
 #[serde(rename_all = "camelCase")]
 pub struct ResultDebugCall {
-    pub result: CallTracerResult,
+    pub result: DebugCall,
 }
 
 #[derive(Debug, Default, Serialize, Deserialize, Clone, PartialEq)]
@@ -734,18 +734,18 @@ pub enum BlockStatus {
 
 /// FlatTracer is always more than one trace, so when we have to trace one transaction it also appeared as many traces
 #[derive(Debug, Serialize, Deserialize, Clone)]
-#[serde(rename_all = "camelCase", untagged)]
+#[serde(untagged)]
 pub enum CallTracerResult {
-    CallTrace(DebugCall),
-    FlattCallTrace(Box<Vec<DebugCallFlat>>),
+    CallTrace(ResultDebugCall),
+    FlattCallTrace(Vec<DebugCallFlat>),
 }
 
 /// For tracing blocks we need to have all traces being combined all together without separation.
 #[derive(Debug, Serialize, Deserialize, Clone)]
-#[serde(rename_all = "camelCase", untagged)]
+#[serde(untagged)]
 pub enum CallTracerOption {
     CallTrace(DebugCall),
-    FlattCallTrace(Box<DebugCallFlat>),
+    FlattCallTrace(Vec<DebugCallFlat>),
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
diff --git a/core/lib/web3_decl/src/namespaces/debug.rs b/core/lib/web3_decl/src/namespaces/debug.rs
index 34372241e847..16e9a431f1f9 100644
--- a/core/lib/web3_decl/src/namespaces/debug.rs
+++ b/core/lib/web3_decl/src/namespaces/debug.rs
@@ -25,14 +25,14 @@ pub trait DebugNamespace {
         &self,
         block: BlockNumber,
         options: Option<TracerConfig>,
-    ) -> RpcResult<Vec<CallTracerOption>>;
+    ) -> RpcResult<Vec<CallTracerResult>>;
 
     #[method(name = "traceBlockByHash")]
     async fn trace_block_by_hash(
         &self,
         hash: H256,
         options: Option<TracerConfig>,
-    ) -> RpcResult<Vec<CallTracerOption>>;
+    ) -> RpcResult<Vec<CallTracerResult>>;
 
     #[method(name = "traceCall")]
     async fn trace_call(
@@ -40,12 +40,12 @@ pub trait DebugNamespace {
         request: CallRequest,
         block: Option<BlockId>,
         options: Option<TracerConfig>,
-    ) -> RpcResult<CallTracerResult>;
+    ) -> RpcResult<CallTracerOption>;
 
     #[method(name = "traceTransaction")]
     async fn trace_transaction(
         &self,
         tx_hash: H256,
         options: Option<TracerConfig>,
-    ) -> RpcResult<Option<CallTracerResult>>;
+    ) -> RpcResult<Option<CallTracerOption>>;
 }
diff --git a/core/node/api_server/src/web3/backend_jsonrpsee/namespaces/debug.rs b/core/node/api_server/src/web3/backend_jsonrpsee/namespaces/debug.rs
index 94f3823dea6d..3696c6b5d7c7 100644
--- a/core/node/api_server/src/web3/backend_jsonrpsee/namespaces/debug.rs
+++ b/core/node/api_server/src/web3/backend_jsonrpsee/namespaces/debug.rs
@@ -16,7 +16,7 @@ impl DebugNamespaceServer for DebugNamespace {
         &self,
         block: BlockNumber,
         options: Option<TracerConfig>,
-    ) -> RpcResult<Vec<CallTracerOption>> {
+    ) -> RpcResult<Vec<CallTracerResult>> {
         self.debug_trace_block_impl(BlockId::Number(block), options)
             .await
             .map_err(|err| self.current_method().map_err(err))
@@ -26,7 +26,7 @@ impl DebugNamespaceServer for DebugNamespace {
         &self,
         hash: H256,
         options: Option<TracerConfig>,
-    ) -> RpcResult<Vec<CallTracerOption>> {
+    ) -> RpcResult<Vec<CallTracerResult>> {
         self.debug_trace_block_impl(BlockId::Hash(hash), options)
             .await
             .map_err(|err| self.current_method().map_err(err))
@@ -37,7 +37,7 @@ impl DebugNamespaceServer for DebugNamespace {
         request: CallRequest,
         block: Option<BlockId>,
         options: Option<TracerConfig>,
-    ) -> RpcResult<CallTracerResult> {
+    ) -> RpcResult<CallTracerOption> {
         self.debug_trace_call_impl(request, block, options)
             .await
             .map_err(|err| self.current_method().map_err(err))
@@ -47,7 +47,7 @@ impl DebugNamespaceServer for DebugNamespace {
         &self,
         tx_hash: H256,
         options: Option<TracerConfig>,
-    ) -> RpcResult<Option<CallTracerResult>> {
+    ) -> RpcResult<Option<CallTracerOption>> {
         self.debug_trace_transaction_impl(tx_hash, options)
             .await
             .map_err(|err| self.current_method().map_err(err))
diff --git a/core/node/api_server/src/web3/namespaces/debug.rs b/core/node/api_server/src/web3/namespaces/debug.rs
index 218d056e73be..3f67f5a2cff0 100644
--- a/core/node/api_server/src/web3/namespaces/debug.rs
+++ b/core/node/api_server/src/web3/namespaces/debug.rs
@@ -10,7 +10,7 @@ use zksync_system_constants::MAX_ENCODED_TX_SIZE;
 use zksync_types::{
     api::{
         BlockId, BlockNumber, CallTracerOption, CallTracerResult, DebugCall, DebugCallType,
-        SupportedTracers, TracerConfig,
+        ResultDebugCall, SupportedTracers, TracerConfig,
     },
     debug_flat_call::{Action, CallResult, DebugCallFlat},
     fee_model::BatchFeeInput,
@@ -58,7 +58,7 @@ impl DebugNamespace {
         index: usize,
         transaction_hash: H256,
         tracer_option: Option<TracerConfig>,
-    ) -> CallTracerResult {
+    ) -> CallTracerOption {
         let (only_top_call, flatten) = tracer_option
             .map(|options| {
                 (
@@ -78,9 +78,9 @@ impl DebugNamespace {
                 index,
                 transaction_hash,
             );
-            CallTracerResult::FlattCallTrace(Box::new(calls))
+            CallTracerOption::FlattCallTrace(calls)
         } else {
-            CallTracerResult::CallTrace(Self::map_default_call(call, only_top_call))
+            CallTracerOption::CallTrace(Self::map_default_call(call, only_top_call))
         }
     }
     pub(crate) fn map_default_call(call: Call, only_top_call: bool) -> DebugCall {
@@ -183,7 +183,7 @@ impl DebugNamespace {
         &self,
         block_id: BlockId,
         options: Option<TracerConfig>,
-    ) -> Result<Vec<CallTracerOption>, Web3Error> {
+    ) -> Result<Vec<CallTracerResult>, Web3Error> {
         self.current_method().set_block_id(block_id);
         if matches!(block_id, BlockId::Number(BlockNumber::Pending)) {
             // See `EthNamespace::get_block_impl()` for an explanation why this check is needed.
@@ -200,30 +200,31 @@ impl DebugNamespace {
             .get_traces_for_l2_block(block_number)
             .await
             .map_err(DalError::generalize)?;
-        let call_trace = call_traces
-            .into_iter()
-            .flat_map(|(call_trace, hash, index)| {
-                match Self::map_call(call_trace, index, hash, options) {
-                    CallTracerResult::CallTrace(call) => {
-                        vec![CallTracerOption::CallTrace(call)]
-                    }
-                    CallTracerResult::FlattCallTrace(call) => call
-                        .into_iter()
-                        .map(Box::new)
-                        .map(CallTracerOption::FlattCallTrace)
-                        .collect(),
+
+        let mut calls = vec![];
+        let mut flat_calls = vec![];
+        for (call_trace, hash, index) in call_traces {
+            match Self::map_call(call_trace, index, hash, options) {
+                CallTracerOption::CallTrace(call) => {
+                    calls.push(CallTracerResult::CallTrace(ResultDebugCall {
+                        result: call,
+                    }))
                 }
-            })
-            .collect();
+                CallTracerOption::FlattCallTrace(mut call) => flat_calls.append(&mut call),
+            }
+        }
+        if calls.is_empty() && !flat_calls.is_empty() {
+            calls.push(CallTracerResult::FlattCallTrace(flat_calls))
+        }
 
-        Ok(call_trace)
+        Ok(calls)
     }
 
     pub async fn debug_trace_transaction_impl(
         &self,
         tx_hash: H256,
         options: Option<TracerConfig>,
-    ) -> Result<Option<CallTracerResult>, Web3Error> {
+    ) -> Result<Option<CallTracerOption>, Web3Error> {
         let mut connection = self.state.acquire_connection().await?;
         let call_trace = connection
             .transactions_dal()
@@ -239,7 +240,7 @@ impl DebugNamespace {
         mut request: CallRequest,
         block_id: Option<BlockId>,
         options: Option<TracerConfig>,
-    ) -> Result<CallTracerResult, Web3Error> {
+    ) -> Result<CallTracerOption, Web3Error> {
         let block_id = block_id.unwrap_or(BlockId::Number(BlockNumber::Pending));
         self.current_method().set_block_id(block_id);
 
diff --git a/core/node/api_server/src/web3/tests/debug.rs b/core/node/api_server/src/web3/tests/debug.rs
index 48450cfc99e8..b1d6a1aed0eb 100644
--- a/core/node/api_server/src/web3/tests/debug.rs
+++ b/core/node/api_server/src/web3/tests/debug.rs
@@ -2,7 +2,10 @@
 
 use zksync_multivm::interface::{Call, TransactionExecutionResult};
 use zksync_types::{
-    api::{CallTracerConfig, CallTracerOption, CallTracerResult, SupportedTracers, TracerConfig},
+    api::{
+        CallTracerConfig, CallTracerOption, CallTracerResult, ResultDebugCall, SupportedTracers,
+        TracerConfig,
+    },
     BOOTLOADER_ADDRESS,
 };
 use zksync_web3_decl::{
@@ -65,7 +68,7 @@ impl HttpTest for TraceBlockTest {
 
             assert_eq!(block_traces.len(), tx_results.len()); // equals to the number of transactions in the block
             for (trace, tx_result) in block_traces.iter().zip(&tx_results) {
-                let CallTracerOption::CallTrace(result) = trace else {
+                let CallTracerResult::CallTrace(ResultDebugCall { result }) = trace else {
                     unreachable!()
                 };
                 assert_eq!(result.from, Address::zero());
@@ -159,9 +162,10 @@ impl HttpTest for TraceBlockFlatTest {
                     .map(|&i| block_traces[i].clone());
 
                 for (top_level_trace, tx_result) in top_level_traces.zip(&tx_results) {
-                    let CallTracerOption::FlattCallTrace(top_level_trace) = top_level_trace else {
+                    let CallTracerResult::FlattCallTrace(top_level_trace) = top_level_trace else {
                         unreachable!()
                     };
+                    let top_level_trace = top_level_trace.first().unwrap();
                     assert_eq!(top_level_trace.action.from, Address::zero());
                     assert_eq!(top_level_trace.action.to, BOOTLOADER_ADDRESS);
                     assert_eq!(
@@ -227,7 +231,7 @@ impl HttpTest for TraceTransactionTest {
             .map(|call| DebugNamespace::map_default_call(call.clone(), false))
             .collect();
 
-        let CallTracerResult::CallTrace(result) = client
+        let CallTracerOption::CallTrace(result) = client
             .trace_transaction(tx_results[0].hash, None)
             .await?
             .context("no transaction traces")?
diff --git a/core/node/api_server/src/web3/tests/vm.rs b/core/node/api_server/src/web3/tests/vm.rs
index 0fdef207e6ca..f8571b62fbcc 100644
--- a/core/node/api_server/src/web3/tests/vm.rs
+++ b/core/node/api_server/src/web3/tests/vm.rs
@@ -7,7 +7,7 @@ use zksync_multivm::interface::{
     ExecutionResult, VmExecutionLogs, VmExecutionResultAndLogs, VmRevertReason,
 };
 use zksync_types::{
-    api::{ApiStorageLog, CallTracerResult},
+    api::{ApiStorageLog, CallTracerOption},
     get_intrinsic_constants,
     transaction_request::CallRequest,
     K256PrivateKey, L2ChainId, PackedEthSignature, StorageLogKind, StorageLogWithPreviousValue,
@@ -430,14 +430,14 @@ impl HttpTest for TraceCallTest {
         drop(connection);
 
         let call_request = CallTest::call_request(b"pending");
-        let CallTracerResult::CallTrace(call_result) =
+        let CallTracerOption::CallTrace(call_result) =
             client.trace_call(call_request.clone(), None, None).await?
         else {
             unreachable!()
         };
         Self::assert_debug_call(&call_request, &call_result);
         let pending_block_number = api::BlockId::Number(api::BlockNumber::Pending);
-        let CallTracerResult::CallTrace(call_result) = client
+        let CallTracerOption::CallTrace(call_result) = client
             .trace_call(call_request.clone(), Some(pending_block_number), None)
             .await?
         else {
@@ -448,7 +448,7 @@ impl HttpTest for TraceCallTest {
         let latest_block_numbers = [api::BlockNumber::Latest, 1.into()];
         let call_request = CallTest::call_request(b"latest");
         for number in latest_block_numbers {
-            let CallTracerResult::CallTrace(call_result) = client
+            let CallTracerOption::CallTrace(call_result) = client
                 .trace_call(
                     call_request.clone(),
                     Some(api::BlockId::Number(number)),
@@ -505,14 +505,14 @@ impl HttpTest for TraceCallTestAfterSnapshotRecovery {
         _pool: &ConnectionPool<Core>,
     ) -> anyhow::Result<()> {
         let call_request = CallTest::call_request(b"pending");
-        let CallTracerResult::CallTrace(call_result) =
+        let CallTracerOption::CallTrace(call_result) =
             client.trace_call(call_request.clone(), None, None).await?
         else {
             unreachable!()
         };
         TraceCallTest::assert_debug_call(&call_request, &call_result);
         let pending_block_number = api::BlockId::Number(api::BlockNumber::Pending);
-        let CallTracerResult::CallTrace(call_result) = client
+        let CallTracerOption::CallTrace(call_result) = client
             .trace_call(call_request.clone(), Some(pending_block_number), None)
             .await?
         else {
@@ -535,7 +535,7 @@ impl HttpTest for TraceCallTestAfterSnapshotRecovery {
         let first_l2_block_numbers = [api::BlockNumber::Latest, first_local_l2_block.0.into()];
         for number in first_l2_block_numbers {
             let number = api::BlockId::Number(number);
-            let CallTracerResult::CallTrace(call_result) = client
+            let CallTracerOption::CallTrace(call_result) = client
                 .trace_call(call_request.clone(), Some(number), None)
                 .await?
             else {
diff --git a/core/tests/ts-integration/tests/api/debug.test.ts b/core/tests/ts-integration/tests/api/debug.test.ts
index 054aa57cf64e..60c51b1a3a94 100644
--- a/core/tests/ts-integration/tests/api/debug.test.ts
+++ b/core/tests/ts-integration/tests/api/debug.test.ts
@@ -75,7 +75,7 @@ describe('Debug methods', () => {
             input: expect.any(String),
             output: '0x',
             to: BOOTLOADER_FORMAL_ADDRESS,
-            type: 'Call',
+            type: 'call',
             value: expect.any(String),
             calls: expect.any(Array)
             // We intentionally skip `error` and `revertReason` fields: the block may contain failing txs
@@ -99,7 +99,7 @@ describe('Debug methods', () => {
             output: '0x',
             revertReason: null,
             to: BOOTLOADER_FORMAL_ADDRESS,
-            type: 'Call',
+            type: 'call',
             value: '0x0',
             calls: expect.any(Array)
         };