diff --git a/rpc.go b/rpc.go
new file mode 100644
index 0000000..708a243
--- /dev/null
+++ b/rpc.go
@@ -0,0 +1,51 @@
+package protocol
+
+// Range of the LSP code space
+const (
+	LspReservedErrorRangeStart = -32899
+	LspReservedErrorRangeEnd   = -32800
+)
+
+// LSP Specific error codes used with JSON RPC.
+const (
+	// Error code indicating that a server received a notification or
+	// request before the server received the `initialize` request.
+	//
+	// For backwards compatibility these codes are not in the LSP range.
+	RPCServerNotInitialized int64 = -32002
+	RPCUnknownErrorCode     int64 = -32001
+
+	// A request failed but it was syntactically correct, e.g the
+	// method name was known and the parameters were valid. The error
+	// message should contain human readable information about why
+	// the request failed.
+	//
+	// @since 3.17.0
+	RPCRequestFailed int64 = -32803
+
+	// The server detected that the content of a document got
+	// modified outside normal conditions. A server should
+	// NOT send this error code if it detects a content change
+	// in its unprocessed messages. The result even computed
+	// on an older state might still be useful for the client.
+	//
+	// If a client decides that a result is not of any use anymore
+	// the client should cancel the request.
+	RPCContentModified int64 = -32801
+
+	// The client has canceled a request and a server has detected
+	// the cancel.
+	RPCRequestCancelled int64 = -32800
+)
+
+func IsLspRPCErrorCode(code int64) bool {
+	if code >= LspReservedErrorRangeStart && code <= LspReservedErrorRangeEnd {
+		return true
+	}
+
+	if code == RPCServerNotInitialized || code == RPCUnknownErrorCode {
+		return true
+	}
+
+	return false
+}
diff --git a/rpc_test.go b/rpc_test.go
new file mode 100644
index 0000000..f827aef
--- /dev/null
+++ b/rpc_test.go
@@ -0,0 +1,38 @@
+package protocol_test
+
+import (
+	"testing"
+
+	"github.com/laravel-ls/protocol"
+)
+
+func Test_IsLspRPCErrorCode(t *testing.T) {
+	if protocol.IsLspRPCErrorCode(5000) {
+		t.Errorf("5000 is not a valid code, but function returned true")
+	}
+
+	if protocol.IsLspRPCErrorCode(-9000) {
+		t.Errorf("-9000 is not a valid code, but function returned true")
+	}
+
+	if protocol.IsLspRPCErrorCode(-32899) == false {
+		t.Errorf("-32899 is a valid code, but function returned false")
+	}
+
+	if protocol.IsLspRPCErrorCode(-32840) == false {
+		t.Errorf("-32840 is a valid code, but function returned false")
+	}
+
+	if protocol.IsLspRPCErrorCode(-32800) == false {
+		t.Errorf("-32800 is a valid code, but function returned false")
+	}
+
+	// Exception
+	if protocol.IsLspRPCErrorCode(-32001) == false {
+		t.Errorf("-32001 is a valid code, but function returned false")
+	}
+
+	if protocol.IsLspRPCErrorCode(-32002) == false {
+		t.Errorf("-32002 is a valid code, but function returned false")
+	}
+}