diff --git a/Makefile b/Makefile
index b2d8e296..c85f089a 100644
--- a/Makefile
+++ b/Makefile
@@ -43,6 +43,7 @@ SRCS = src/main.c \
        src/lexer/token.c \
        src/analysis/typecheck.c \
        src/lsp/json_rpc.c \
+       src/lsp/json_rpc_error.c \
        src/lsp/lsp_main.c \
        src/lsp/lsp_analysis.c \
        src/lsp/lsp_index.c \
@@ -192,6 +193,7 @@ test: $(TARGET) $(PLUGINS)
 	./tests/run_tests.sh
 	./tests/run_codegen_tests.sh
 	./tests/run_example_transpile.sh
+	./tests/run_lsp_tests.sh
 
 # Build with alternative compilers
 zig:
diff --git a/src/lsp/json_rpc.c b/src/lsp/json_rpc.c
index ffb5d1fd..d22fc66a 100644
--- a/src/lsp/json_rpc.c
+++ b/src/lsp/json_rpc.c
@@ -1,11 +1,13 @@
 #include "json_rpc.h"
 #include "cJSON.h"
 #include "lsp_project.h"
+#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdbool.h>
 
-void lsp_check_file(const char *uri, const char *src, int id);
+void lsp_check_file(const char *uri, const char *src);
 void lsp_goto_definition(const char *uri, int line, int col, int id);
 void lsp_hover(const char *uri, int line, int col, int id);
 void lsp_completion(const char *uri, int line, int col, int id);
@@ -48,6 +50,203 @@ static void get_params(cJSON *root, char **uri, int *line, int *col)
     }
 }
 
+void send_lsp_message_json(const cJSON *json)
+{
+    char *body;
+    size_t len;
+
+    assert(json);
+
+    body = cJSON_PrintUnformatted(json);
+
+    len = strlen(body);
+
+    fprintf(stdout, "Content-Length: %zu\r\n\r\n", len);
+    fwrite(body, 1, len, stdout);
+    fflush(stdout);
+
+    free(body);
+}
+
+cJSON *create_response(const cJSON *id_item,
+                       const cJSON *result,
+                       const cJSON *error)
+{
+    cJSON *res;
+
+    assert(id_item || (error && !id_item));
+    assert((result && !error) || (!result && error));
+
+    res = cJSON_CreateObject();
+    if (!res) {
+        return NULL;
+    }
+
+    cJSON_AddStringToObject(res, "jsonrpc", "2.0");
+
+    cJSON_AddItemToObject(res, "id", cJSON_Duplicate(id_item, 1));
+
+    if (result)
+	{
+        cJSON_AddItemToObject(res, "result", cJSON_Duplicate(result, 1));
+    }
+    else {
+        cJSON_AddItemToObject(res, "error", cJSON_Duplicate(error, 1));
+    }
+
+    return res;
+}
+
+void handle_initialize(const cJSON *json, const cJSON *id_item)
+{
+	cJSON *params = cJSON_GetObjectItem(json, "params");
+	char *root = NULL;
+	if (params)
+	{
+		cJSON *rp = cJSON_GetObjectItem(params, "rootPath");
+		if (rp && rp->valuestring)
+		{
+			root = strdup(rp->valuestring);
+		}
+		else
+		{
+			cJSON *ru = cJSON_GetObjectItem(params, "rootUri");
+			if (ru && ru->valuestring)
+			{
+				root = strdup(ru->valuestring);
+			}
+		}
+	}
+
+	if (root && strncmp(root, "file://", 7) == 0)
+	{
+		char *clean = strdup(root + 7);
+		free(root);
+		root = clean;
+	}
+
+	lsp_project_init(root ? root : ".");
+	if (root)
+	{
+		free(root);
+	}
+
+	cJSON *result = cJSON_CreateObject();
+
+    cJSON *serverInfo = cJSON_AddObjectToObject(result, "serverInfo");
+    cJSON_AddStringToObject(serverInfo, "name", "ZenC LS");
+    cJSON_AddStringToObject(serverInfo, "version", "1.0.0");
+
+    // server capabilities
+    cJSON *caps = cJSON_AddObjectToObject(result, "capabilities");
+
+    cJSON *sync = cJSON_AddObjectToObject(caps, "textDocumentSync");
+    cJSON_AddBoolToObject(sync, "openClose", true);
+    cJSON_AddNumberToObject(sync, "change", 1);
+
+    cJSON_AddBoolToObject(caps, "definitionProvider", true);
+    cJSON_AddBoolToObject(caps, "hoverProvider", true);
+    cJSON_AddBoolToObject(caps, "referencesProvider", true);
+    cJSON_AddBoolToObject(caps, "documentSymbolProvider", true);
+
+    cJSON *sig = cJSON_AddObjectToObject(caps, "signatureHelpProvider");
+    cJSON *sig_trig = cJSON_AddArrayToObject(sig, "triggerCharacters");
+    cJSON_AddItemToArray(sig_trig, cJSON_CreateString("("));
+
+    cJSON *comp = cJSON_AddObjectToObject(caps, "completionProvider");
+    cJSON *comp_trig = cJSON_AddArrayToObject(comp, "triggerCharacters");
+    cJSON_AddItemToArray(comp_trig, cJSON_CreateString("."));
+
+    cJSON *response = create_response(id_item, result, NULL);
+    send_lsp_message_json(response);
+
+    cJSON_Delete(result);
+    cJSON_Delete(response);
+}
+
+void handle_shutdown(cJSON *id_item)
+{
+    assert(id_item);
+
+    fprintf(stderr, "zls: shutdown received\n");
+
+    // lsp_state.shutdown = 1;
+	// TODO: after shutdown every request except exit gonna send JSONRPC_INVALID_REQUEST
+
+    cJSON *result = cJSON_CreateNull();
+
+    cJSON *response = create_response(id_item, result, NULL);
+
+    send_lsp_message_json(response);
+
+    cJSON_Delete(result);
+    cJSON_Delete(response);
+}
+
+void handle_exit(void)
+{
+    fprintf(stderr, "zls: exit received\n");
+    // TODO: add the lsp clean here
+	
+    // TODO: exit 0 if shutdown is call before exit else exit 1 
+    exit(0);
+}
+
+void handle_did_open(const cJSON *json)
+{
+	cJSON *params = cJSON_GetObjectItem(json, "params");
+	if (!params)
+	{
+		return;
+	}
+	cJSON *doc = cJSON_GetObjectItem(params, "textDocument");
+	if (!doc)
+	{
+		return;
+	}
+	cJSON *uri = cJSON_GetObjectItem(doc, "uri");
+	if (!uri || !cJSON_IsString(uri))
+	{
+		return;
+	}
+	cJSON *text = cJSON_GetObjectItem(doc, "text");
+	if (!text || !cJSON_IsString(text))
+	{
+		return;
+	}
+	lsp_check_file(uri->valuestring, text->valuestring);
+}
+
+void handle_did_change(const cJSON *json)
+{
+	cJSON *params = cJSON_GetObjectItem(json, "params");
+	if (!params)
+	{
+		return;
+	}
+	cJSON *changes = cJSON_GetObjectItem(params, "contentChanges");
+	if (!changes)
+	{
+		return;
+	}
+	cJSON *doc = cJSON_GetObjectItem(params, "textDocument");
+	if (!doc)
+	{
+		return;
+	}
+	cJSON *uri = cJSON_GetObjectItem(doc, "uri");
+	if (!uri || !cJSON_IsString(uri))
+	{
+		return;
+	}
+	cJSON *text = cJSON_GetObjectItem(changes, "text");
+	if (!text || !cJSON_IsString(text))
+	{
+		return;
+	}
+	lsp_check_file(uri->valuestring, text->valuestring);
+}
+
 void handle_request(const char *json_str)
 {
     cJSON *json = cJSON_Parse(json_str);
@@ -58,14 +257,22 @@ void handle_request(const char *json_str)
 
     int id = 0;
     cJSON *id_item = cJSON_GetObjectItem(json, "id");
-    if (id_item)
-    {
-        id = id_item->valueint;
-    }
+	if (id_item && !(cJSON_IsNumber(id_item) || cJSON_IsString(id_item)))
+	{
+		invalid_request(NULL);
+		cJSON_Delete(json);
+		return;
+	}
+	if (id_item)
+	{
+		// FIXME: not always int but can be string too
+		id = id_item->valueint;
+	}
 
     cJSON *method_item = cJSON_GetObjectItem(json, "method");
-    if (!method_item || !method_item->valuestring)
+    if (!method_item || !cJSON_IsString(method_item))
     {
+		invalid_request(id_item);
         cJSON_Delete(json);
         return;
     }
@@ -73,79 +280,16 @@ void handle_request(const char *json_str)
 
     if (strcmp(method, "initialize") == 0)
     {
-        cJSON *params = cJSON_GetObjectItem(json, "params");
-        char *root = NULL;
-        if (params)
-        {
-            cJSON *rp = cJSON_GetObjectItem(params, "rootPath");
-            if (rp && rp->valuestring)
-            {
-                root = strdup(rp->valuestring);
-            }
-            else
-            {
-                cJSON *ru = cJSON_GetObjectItem(params, "rootUri");
-                if (ru && ru->valuestring)
-                {
-                    root = strdup(ru->valuestring);
-                }
-            }
-        }
-
-        if (root && strncmp(root, "file://", 7) == 0)
-        {
-            char *clean = strdup(root + 7);
-            free(root);
-            root = clean;
-        }
-
-        lsp_project_init(root ? root : ".");
-        if (root)
-        {
-            free(root);
-        }
-
-        const char *response =
-            "{\"jsonrpc\":\"2.0\",\"id\":0,\"result\":{"
-            "\"serverInfo\":{\"name\":\"ZenC LS\",\"version\": \"1.0.0\"},"
-            "\"capabilities\":{\"textDocumentSync\":{\"openClose\":true,\"change\":1},"
-            "\"definitionProvider\":true,\"hoverProvider\":true,"
-            "\"referencesProvider\":true,\"documentSymbolProvider\":true,"
-            "\"signatureHelpProvider\":{\"triggerCharacters\":[\"(\"]},"
-            "\"completionProvider\":{"
-            "\"triggerCharacters\":[\".\"]}}}}";
-        fprintf(stdout, "Content-Length: %zu\r\n\r\n%s", strlen(response), response);
-        fflush(stdout);
-    }
-    else if (strcmp(method, "textDocument/didOpen") == 0 ||
-             strcmp(method, "textDocument/didChange") == 0)
-    {
-        cJSON *params = cJSON_GetObjectItem(json, "params");
-        if (params)
-        {
-            cJSON *doc = cJSON_GetObjectItem(params, "textDocument");
-            if (doc)
-            {
-                cJSON *uri = cJSON_GetObjectItem(doc, "uri");
-                cJSON *text = cJSON_GetObjectItem(doc, "text");
-                // For didChange, text is inside contentChanges
-                if (!text && strcmp(method, "textDocument/didChange") == 0)
-                {
-                    cJSON *changes = cJSON_GetObjectItem(params, "contentChanges");
-                    if (changes && cJSON_GetArraySize(changes) > 0)
-                    {
-                        cJSON *change = cJSON_GetArrayItem(changes, 0);
-                        text = cJSON_GetObjectItem(change, "text");
-                    }
-                }
-
-                if (uri && uri->valuestring && text && text->valuestring)
-                {
-                    lsp_check_file(uri->valuestring, text->valuestring, id);
-                }
-            }
-        }
+        handle_initialize(json, id_item);
     }
+    else if (strcmp(method, "textDocument/didOpen") == 0)
+	{
+		handle_did_open(json);
+	}
+    else if (strcmp(method, "textDocument/didChange") == 0)
+	{
+		handle_did_change(json);
+	}
     else if (strcmp(method, "textDocument/definition") == 0)
     {
         char *uri = NULL;
@@ -212,6 +356,18 @@ void handle_request(const char *json_str)
             free(uri);
         }
     }
+    else if (strcmp(method, "shutdown") == 0)
+	{
+		handle_shutdown(id_item);
+	}
+    else if (strcmp(method, "exit") == 0)
+	{
+		handle_exit();
+	}
+    else 
+	{
+		method_not_found(id_item);
+	}
 
     cJSON_Delete(json);
 }
diff --git a/src/lsp/json_rpc.h b/src/lsp/json_rpc.h
index 0a5c2821..f88e3d0f 100644
--- a/src/lsp/json_rpc.h
+++ b/src/lsp/json_rpc.h
@@ -2,6 +2,18 @@
 #ifndef JSON_RPC_H
 #define JSON_RPC_H
 
+#include "cJSON.h"
+
+typedef enum jsonrpc_error_t
+{
+    JSONRPC_PARSE_ERROR     = -32700,
+    JSONRPC_INVALID_REQUEST = -32600,
+    JSONRPC_METHOD_NOT_FOUND= -32601,
+    JSONRPC_INVALID_PARAMS  = -32602,
+    JSONRPC_INTERNAL_ERROR  = -32603,
+} jsonrpc_error_t;
+
+
 /**
  * @brief Handle a raw JSON-RPC request string.
  *
@@ -12,4 +24,17 @@
  */
 void handle_request(const char *json_str);
 
+void method_not_found(const cJSON *id_item);
+void internal_error(const cJSON *id_item);
+void parse_error(const cJSON *id_item);
+void invalid_params(const cJSON *id_item);
+void invalid_request(const cJSON *id_item);
+
+cJSON *create_response(const cJSON *id_item,
+                       const cJSON *result,
+                       const cJSON *error);
+
+void send_lsp_message_json(const cJSON *json);
+
+
 #endif
diff --git a/src/lsp/json_rpc_error.c b/src/lsp/json_rpc_error.c
new file mode 100644
index 00000000..196d082c
--- /dev/null
+++ b/src/lsp/json_rpc_error.c
@@ -0,0 +1,81 @@
+
+#include "json_rpc.h"
+#include <assert.h>
+
+cJSON *create_error(const jsonrpc_error_t err_code,
+                       const char *err_msg)
+{
+    cJSON *res;
+
+    assert(err_msg);
+
+    res = cJSON_CreateObject();
+	cJSON_AddNumberToObject(res, "code", err_code);
+	cJSON_AddStringToObject(res, "message", err_msg);
+
+    return res;
+}
+
+void send_error(const cJSON *id_item, const jsonrpc_error_t err_code, const char *err_msg)
+{
+	cJSON *err = create_error(err_code, err_msg);
+	cJSON *res = create_response(id_item, NULL, err);
+
+	send_lsp_message_json(res);
+
+	cJSON_Delete(err);
+	cJSON_Delete(res);
+}
+
+const char *jsonrpc_error_message(jsonrpc_error_t code)
+{
+    switch (code) {
+        case JSONRPC_PARSE_ERROR: return "Parse error";
+        case JSONRPC_INVALID_REQUEST: return "Invalid Request";
+        case JSONRPC_METHOD_NOT_FOUND: return "Method not found";
+        case JSONRPC_INVALID_PARAMS: return "Invalid params";
+        case JSONRPC_INTERNAL_ERROR: return "Internal error";
+        default: return "Unknown error";
+    }
+}
+
+
+void method_not_found(const cJSON *id_item)
+{
+	const jsonrpc_error_t err_code = JSONRPC_METHOD_NOT_FOUND;
+	const char *msg = jsonrpc_error_message(err_code);
+
+	send_error(id_item, err_code, msg);
+}
+
+void parse_error(const cJSON *id_item)
+{
+	const jsonrpc_error_t err_code = JSONRPC_PARSE_ERROR; 
+	const char *msg = jsonrpc_error_message(err_code);
+
+	send_error(id_item, err_code, msg);
+}
+
+void invalid_request(const cJSON *id_item)
+{
+	const jsonrpc_error_t err_code = JSONRPC_INVALID_REQUEST; 
+	const char *msg = jsonrpc_error_message(err_code);
+
+	send_error(id_item, err_code, msg);
+}
+
+void invalid_params(const cJSON *id_item)
+{
+	const jsonrpc_error_t err_code = JSONRPC_INVALID_PARAMS;
+	const char *msg = jsonrpc_error_message(err_code);
+
+	send_error(id_item, err_code, msg);
+}
+
+void internal_error(const cJSON *id_item)
+{
+	const jsonrpc_error_t err_code = JSONRPC_INTERNAL_ERROR; 
+	const char *msg = jsonrpc_error_message(err_code);
+
+	send_error(id_item, err_code, msg);
+}
\ No newline at end of file
diff --git a/src/lsp/lsp_analysis.c b/src/lsp/lsp_analysis.c
index 0367d930..dbe74653 100644
--- a/src/lsp/lsp_analysis.c
+++ b/src/lsp/lsp_analysis.c
@@ -56,7 +56,7 @@ void lsp_on_error(void *data, Token t, const char *msg)
     }
 }
 
-void lsp_check_file(const char *uri, const char *json_src, int id)
+void lsp_check_file(const char *uri, const char *json_src)
 {
     if (!g_project)
     {
@@ -93,7 +93,6 @@ void lsp_check_file(const char *uri, const char *json_src, int id)
     // Construct JSON Response (publishDiagnostics)
     cJSON *root = cJSON_CreateObject();
     cJSON_AddStringToObject(root, "jsonrpc", "2.0");
-    cJSON_AddNumberToObject(root, "id", id);
     cJSON_AddStringToObject(root, "method", "textDocument/publishDiagnostics");
 
     cJSON *params = cJSON_CreateObject();
diff --git a/tests/run_lsp_tests.sh b/tests/run_lsp_tests.sh
new file mode 100755
index 00000000..fda7e8c5
--- /dev/null
+++ b/tests/run_lsp_tests.sh
@@ -0,0 +1,115 @@
+#!/usr/bin/env bash
+# LSP Protocol Compliance Test Suite
+# Usage: ./run_lsp_tests.sh
+
+ZC="./zc"
+GREEN='\033[0;32m'
+RED='\033[0;31m'
+NC='\033[0m'
+
+PASSED=0
+FAILED=0
+FAILED_TESTS=()
+
+send_lsp_message() {
+    local json="$1"
+    local len
+    len=$(printf '%s' "$json" | wc -c)
+
+    response=$(printf "Content-Length: %d\r\n\r\n%s" "$len" "$json" | "$ZC" lsp 2>/dev/null)
+    printf '%s' "$response"
+}
+
+check_response() {
+    local response="$1"
+    local name="$2"
+    local expected_id="$3"
+    local expect_error="${4:-0}"
+    local is_notification="${5:-0}"
+
+    local status="FAIL"
+    local detail=""
+
+    if [[ $is_notification -eq 1 ]]; then
+        if [[ -z "$response" ]]; then
+            status="PASS"
+        else
+            detail="→ got response but notification should be silent"
+        fi
+    elif [[ -z "$response" ]]; then
+        if [[ $expect_error -eq 1 ]]; then
+            status="PASS"
+            detail="→ no response (correct for invalid request)"
+        else
+            detail="→ no response received"
+        fi
+    else
+        id=$(echo "$response" | grep -oP '"id":\s*(\d+|"[a-zA-Z0-9]+?"|\[[^\]]+\]|true|false|null)' | head -1 | cut -d: -f2- | tr -d ' "')
+
+        has_error=$(echo "$response" | grep -c '"error"' || true)
+        has_result=$(echo "$response" | grep -c '"result"' || true)
+
+        if [[ $expect_error -eq 1 ]]; then
+            [[ $has_error -gt 0 ]] && status="PASS" || detail="→ expected error but none found"
+        else
+            if [[ "$id" = "$expected_id" ]]; then
+                if [[ $has_result -gt 0 ]]; then
+                    status="PASS"
+                elif [[ $has_error -gt 0 ]]; then
+                    detail="→ got error instead of result"
+                else
+                    detail="→ missing both result & error"
+                fi
+            else
+                detail="→ id mismatch (got '$id', expected '$expected_id')"
+            fi
+        fi
+    fi
+
+    if [[ $status = "PASS" ]]; then
+        echo -e "Testing $name... PASS"
+        ((PASSED++))
+    else
+        echo -e "Testing $name... FAIL$"
+        [[ -n "$detail" ]] && echo "    $detail"
+        ((FAILED++))
+        FAILED_TESTS+=("$name")
+    fi
+}
+
+# ────────────────────────────────────────────────
+echo "Running LSP Compliance Tests..."
+echo
+
+# ALL tests
+
+response=$(send_lsp_message '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"rootUri":"file:///tmp"}}')
+check_response "$response" "initialize (id=1)" "1" 0 0
+
+response=$(send_lsp_message '{"jsonrpc":"2.0","id":"abc","method":"initialize","params":{"rootUri":"file:///tmp"}}')
+check_response "$response" "initialize (id=\"abc\")" "abc" 0 0
+
+response=$(send_lsp_message '{"jsonrpc":"2.0","id":true,"method":"initialize","params":{"rootUri":"file:///tmp"}}')
+check_response "$response" "initialize (invalid id=true)" "true" 1 0
+
+response=$(send_lsp_message '{"jsonrpc":"2.0","id":[1,2],"method":"initialize","params":{"rootUri":"file:///tmp"}}')
+check_response "$response" "initialize (invalid id=array)" "[1,2]" 1 0
+
+response=$(send_lsp_message '{"jsonrpc":"2.0","method":"initialize","params":{"rootUri":"file:///tmp"}}')
+check_response "$response" "initialize as notification (no id)" "" 1 0
+
+response=$(send_lsp_message '{"jsonrpc":"2.0","id":2,"method":"shutdown","params":null}')
+check_response "$response" "shutdown (id=2)" "2" 0 0
+
+response=$(send_lsp_message '{"jsonrpc":"2.0","method":"exit"}')
+check_response "$response" "exit notification" "" 0 1
+
+response=$(send_lsp_message '{"jsonrpc":"2.0","id":99,"method":"unknownMethod","params":{}}')
+check_response "$response" "unknown method" "99" 1 0
+
+echo
+echo "----------------------------------------"
+echo "Summary:"
+echo "-> Passed: $PASSED"
+echo "-> Failed: $FAILED"
+echo "----------------------------------------"
\ No newline at end of file