diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3f50fc6c..5d271919 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -232,10 +232,12 @@ endif()
 
 set(PUBLICHEADERS
     include/aare/ClusterFinder.hpp
+    include/aare/CtbRawFile.hpp
     include/aare/defs.hpp
     include/aare/Dtype.hpp
     include/aare/File.hpp
     include/aare/FileInterface.hpp
+    include/aare/file_utils.hpp
     include/aare/Frame.hpp
     include/aare/json.hpp
     include/aare/NDArray.hpp
@@ -253,9 +255,11 @@ set(PUBLICHEADERS
 
 set(SourceFiles
     ${CMAKE_CURRENT_SOURCE_DIR}/src/defs.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/src/CtbRawFile.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/Dtype.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/Frame.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/File.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/src/file_utils.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/NumpyFile.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/PixelMap.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/RawFile.cpp
@@ -286,6 +290,7 @@ if(AARE_TESTS)
             ${CMAKE_CURRENT_SOURCE_DIR}/src/defs.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/Dtype.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/Frame.test.cpp
+            ${CMAKE_CURRENT_SOURCE_DIR}/src/file_utils.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/NDArray.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/NDView.test.cpp
             ${CMAKE_CURRENT_SOURCE_DIR}/src/ClusterFinder.test.cpp
diff --git a/include/aare/CtbRawFile.hpp b/include/aare/CtbRawFile.hpp
new file mode 100644
index 00000000..8dbd1aad
--- /dev/null
+++ b/include/aare/CtbRawFile.hpp
@@ -0,0 +1,20 @@
+#pragma once
+
+#include "aare/FileInterface.hpp"
+#include "aare/file_utils.hpp"
+#include "aare/Frame.hpp"
+
+#include <filesystem>
+
+namespace aare{
+
+class CtbRawFile{
+    FileNameComponents m_fnc{};
+public:
+    CtbRawFile(const std::filesystem::path &fname);
+
+
+
+};
+
+}
\ No newline at end of file
diff --git a/include/aare/file_utils.hpp b/include/aare/file_utils.hpp
new file mode 100644
index 00000000..abccfb6b
--- /dev/null
+++ b/include/aare/file_utils.hpp
@@ -0,0 +1,119 @@
+#pragma once
+#include "aare/defs.hpp"
+#include <filesystem>
+#include <fmt/format.h>
+#include <fstream>
+
+#include <nlohmann/json.hpp>
+using json = nlohmann::json;
+
+namespace aare {
+bool is_master_file(const std::filesystem::path &fpath);
+
+
+struct FileNameComponents {
+    std::filesystem::path base_path{};
+    std::string base_name{};
+    std::string ext{};
+    int findex{};
+    bool valid{false}; // TODO! how do we do error handling?
+
+    std::filesystem::path master_fname() const {
+        return base_path /
+               fmt::format("{}_master_{}{}", base_name, findex, ext);
+    }
+
+    std::filesystem::path data_fname(size_t mod_id, size_t file_id) {
+        return base_path / fmt::format("{}_d{}_f{}_{}.raw", base_name, file_id,
+                                       mod_id, findex);
+    }
+};
+
+FileNameComponents parse_fname(const std::filesystem::path &fname);
+
+class MasterFile {
+    FileNameComponents m_fnc;
+    std::string m_version;
+    DetectorType m_type;
+    TimingMode m_timing_mode;
+    size_t m_total_frames;
+    size_t m_subfile_rows;
+    size_t m_subfile_cols;
+    size_t m_bitdepth;
+    size_t m_analog_samples;
+    size_t m_digital_samples;
+    size_t m_max_frames_per_file;
+    uint32_t m_adc_mask;
+public:
+    MasterFile(const std::filesystem::path &fpath) {
+        m_fnc = parse_fname(fpath);
+
+        
+
+        std::ifstream ifs(fpath);
+        json j;
+        ifs >> j;
+        double v = j["Version"];
+        m_version = fmt::format("{:.1f}", v);
+
+        m_type = StringTo<DetectorType>(j["Detector// Type"].get<std::string>()); 
+        m_timing_mode =
+        StringTo<TimingMode>(j["Timing Mode"].get<std::string>());
+        m_total_frames = j["Frames in File"];
+        m_subfile_rows = j["Pixels"]["y"];
+        m_subfile_cols = j["Pixels"]["x"];
+        m_max_frames_per_file = j["Max Frames Per File"];
+        try {
+            m_bitdepth = j.at("Dynamic Range");
+        } catch (const json::out_of_range &e) {
+            m_bitdepth = 16;
+        }
+
+        try {
+            m_analog_samples = j.at("Analog Samples");
+        }catch (const json::out_of_range &e) {
+            m_analog_samples = 0;
+        }
+        try{
+            std::string adc_mask = j.at("ADC Mask");
+            m_adc_mask = std::stoul(adc_mask, nullptr, 16);
+        }catch (const json::out_of_range &e) {
+            m_adc_mask = 0;
+        }
+
+        try {
+            m_digital_samples = j.at("Digital Samples");
+            }catch (const json::out_of_range &e) {
+            m_digital_samples = 0;
+        }
+
+        //Update detector type for Moench
+        //TODO! How does this work with old .raw master files?
+        if (m_type == DetectorType::Moench && m_analog_samples == 0 &&
+        m_subfile_rows == 400) {
+            m_type = DetectorType::Moench03;
+        }else if (m_type == DetectorType::Moench && m_subfile_rows == 400 &&
+        m_analog_samples == 5000) {
+            m_type = DetectorType::Moench03_old;
+        }
+
+        // //Here we know we have a ChipTestBoard file update the geometry?
+        // //TODO! Carry on information about digtial, and transceivers
+        // if (m_type == DetectorType::ChipTestBoard) {
+        //    subfile_rows = 1;
+        //    subfile_cols = m_analog_samples*__builtin_popcount(m_adc_mask);
+        // }
+
+        // // only Eiger had quad
+        // if (m_type == DetectorType::Eiger) {
+        //     quad = (j["Quad"] == 1);
+        // }
+
+        // m_geometry = {j["Geometry"]["y"], j["Geometry"]["x"]};
+    }
+
+};
+
+
+
+} // namespace aare
\ No newline at end of file
diff --git a/python/src/file.hpp b/python/src/file.hpp
index 65f841db..88bf7476 100644
--- a/python/src/file.hpp
+++ b/python/src/file.hpp
@@ -1,5 +1,6 @@
 #include "aare/Frame.hpp"
 #include "aare/File.hpp"
+#include "aare/CtbRawFile.hpp"
 #include "aare/defs.hpp"
 // #include "aare/fClusterFileV2.hpp"
 
@@ -16,6 +17,11 @@ namespace py = pybind11;
 using namespace::aare;
 
 void define_file_io_bindings(py::module &m) {
+
+    py::class_<CtbRawFile>(m, "CtbRawFile")
+        .def(py::init<const std::filesystem::path &>());
+        
+
     py::class_<File>(m, "File")
         .def(py::init([](const std::filesystem::path &fname) { return File(fname, "r", {}); }))
         .def(
diff --git a/src/CtbRawFile.cpp b/src/CtbRawFile.cpp
new file mode 100644
index 00000000..b70b44fd
--- /dev/null
+++ b/src/CtbRawFile.cpp
@@ -0,0 +1,22 @@
+#include "aare/CtbRawFile.hpp"
+
+
+
+namespace aare{
+
+CtbRawFile::CtbRawFile(const std::filesystem::path &fname){
+
+    if(!std::filesystem::exists(fname)){
+        throw std::runtime_error(LOCATION + "File does not exist");
+    }
+    
+    m_fnc = parse_fname(fname);
+    if(!m_fnc.valid){
+        throw std::runtime_error(LOCATION + "Could not parse master file name");
+    }
+
+
+}
+
+
+} // namespace aare
\ No newline at end of file
diff --git a/src/RawFile.cpp b/src/RawFile.cpp
index eab6e729..ef623ce2 100644
--- a/src/RawFile.cpp
+++ b/src/RawFile.cpp
@@ -71,11 +71,11 @@ void RawFile::find_number_of_subfiles() {
         ;
     n_subfiles = n_mod;
 }
-inline std::filesystem::path RawFile::data_fname(size_t mod_id, size_t file_id) {
+std::filesystem::path RawFile::data_fname(size_t mod_id, size_t file_id) {
     return this->m_base_path / fmt::format("{}_d{}_f{}_{}.raw", this->m_base_name, file_id, mod_id, this->m_findex);
 }
 
-inline std::filesystem::path RawFile::master_fname() {
+std::filesystem::path RawFile::master_fname() {
     return this->m_base_path / fmt::format("{}_master_{}{}", this->m_base_name, this->m_findex, this->m_ext);
 }
 
diff --git a/src/file_utils.cpp b/src/file_utils.cpp
new file mode 100644
index 00000000..01f0e441
--- /dev/null
+++ b/src/file_utils.cpp
@@ -0,0 +1,33 @@
+#include "aare/file_utils.hpp"
+
+namespace aare {
+
+
+
+bool is_master_file(const std::filesystem::path &fpath) {
+    std::string const stem = fpath.stem().string();
+    return stem.find("_master_") != std::string::npos;
+}
+
+FileNameComponents parse_fname(const std::filesystem::path &fname) {
+    FileNameComponents fnc;
+    fnc.base_path = fname.parent_path();
+    fnc.base_name = fname.stem();
+    fnc.ext = fname.extension();
+    try {
+        auto pos = fnc.base_name.rfind('_');
+        fnc.findex = std::stoi(fnc.base_name.substr(pos + 1));
+    } catch (const std::invalid_argument &e) {
+        fnc.valid = false;
+    }
+    auto pos = fnc.base_name.find("_master_");
+    if (pos != std::string::npos) {
+        fnc.base_name.erase(pos);
+    }else{
+        fnc.valid = false;
+    }
+    fnc.valid = true;
+    return fnc;
+}
+
+} // namespace aare
\ No newline at end of file
diff --git a/src/file_utils.test.cpp b/src/file_utils.test.cpp
new file mode 100644
index 00000000..e46ac3d8
--- /dev/null
+++ b/src/file_utils.test.cpp
@@ -0,0 +1,20 @@
+#include "aare/file_utils.hpp"
+
+#include <catch2/catch_test_macros.hpp>
+
+using namespace aare;
+
+TEST_CASE("Use filename to determine if it is a master file") {
+
+    REQUIRE(is_master_file("test_master_1.json"));
+}
+
+TEST_CASE("Parse a master file fname"){
+    auto fnc = parse_fname("test_master_1.json");
+    REQUIRE(fnc.base_name == "test");
+    REQUIRE(fnc.ext == ".json");
+    REQUIRE(fnc.findex == 1);
+
+    REQUIRE(fnc.master_fname() == "test_master_1.json");
+    REQUIRE(fnc.data_fname(1, 2) == "test_d2_f1_1.raw");
+}
\ No newline at end of file