diff --git a/src/fs.c b/src/fs.c
index 8f55f81..a7f83c0 100644
--- a/src/fs.c
+++ b/src/fs.c
@@ -11,7 +11,9 @@
 
 #include "fs.h"
 #include "includes.h"
+#include "index.h"
 #include "objects.h"
+#include "utils.h"
 
 int local_repo_exist()
 {
@@ -19,30 +21,133 @@ int local_repo_exist()
     return stat(LOCAL_REPO, &buffer) == 0;
 }
 
+int index_exist()
+{
+    struct stat buffer;
+    return stat(INDEX_FILE, &buffer) == 0;
+}
+
+void dump_index(struct index *index)
+{
+    printf("index:\n");
+    printf("\tentries_size: %ld\n", index->entries_size);
+    printf("\tentries:\n");
+    struct entry *current = index->first_entry;
+    for(int i = 0; i < index->entries_size; i ++)
+    {
+        printf("\t\tfilename: %s, checksum: %s\n", current->filename, current->checksum);
+        current = current->next;
+    }
+}
+
+int load_index(struct index *index)
+{
+    if(!local_repo_exist() || !index_exist())
+    {
+        return REPO_NOT_INITIALIZED;
+    }
+
+    FILE* index_file = fopen(INDEX_FILE, "r");
+    struct stat buffer;
+    stat(INDEX_FILE, &buffer);
+
+    char* file_content = calloc(sizeof(char), buffer.st_size + 1);
+    fread(file_content, buffer.st_size, 1, index_file);
+    fclose(index_file);
+
+    char* current_line;
+    current_line = strtok(file_content, "\n");
+    index->entries_size = strtol(current_line, NULL, 10);
+    
+    for(int i = 0; i < index->entries_size; i++)
+    {
+        current_line = strtok(NULL, "\n");
+        int j = 0;
+        while(current_line[j] != ' ')
+        {
+            j++;
+        }
+
+        char* checksum = calloc(sizeof(char), j + 1);
+        char* filename = calloc(sizeof(char), strlen(current_line) - j);
+        strncat(checksum, current_line, j);
+        strncat(filename, current_line + j + 1, strlen(current_line) - j);
+
+        struct entry *entry = malloc(sizeof(struct entry));
+        entry->checksum = checksum;
+        entry->filename = filename;
+        entry->next = NULL;
+
+        if(i == 0)
+        {
+            index->first_entry = entry;
+        } else 
+        {
+            entry->previous = index->last_entry;
+            index->last_entry->next = entry;
+        }
+        index->last_entry = entry;
+        debug_print("checksum: %s, filename: %s", entry->checksum, entry->filename);
+    }
+
+    free(file_content);
+
+    return FS_OK;
+}
+
+int save_index(struct index *index)
+{
+    if(!local_repo_exist())
+    {
+        return REPO_NOT_INITIALIZED;
+    }
+
+    FILE *index_file = fopen(INDEX_FILE, "w");
+    if(index_exist == NULL)
+    {
+        return FS_ERROR;
+    }
+
+    fprintf(index_file, "%li\n", index->entries_size);
+
+    struct entry *current = index->first_entry;
+    for(int i = 0; i < index->entries_size; i++)
+    {
+        fprintf(index_file, "%s %s\n", current->checksum, current->filename);
+        current = current->next;
+    }
+
+    fclose(index_file);
+}
+
 int write_object(struct object *obj)
 {
     if(!local_repo_exist())
     {
-        return -2;
+        return REPO_NOT_INITIALIZED;
     }
-    int result = 0;
+    int result = FS_OK;
 
     struct stat buffer;
-    if (stat(LOCAL_REPO"/objects", &buffer) != 0)
+    if (stat(OBJECTS_REPO, &buffer) != 0)
     {
-        mkdir(LOCAL_REPO"/objects", DEFAULT_DIR_MODE);
+        mkdir(OBJECTS_REPO, DEFAULT_DIR_MODE);
     }
     
-    DIR *objects_dir = opendir(LOCAL_REPO"/objects");
+    DIR *objects_dir = opendir(OBJECTS_REPO);
     int objects_dir_fd = dirfd(objects_dir);
 
     char checksum[DIGEST_LENGTH * 2];
     hash_object(obj, checksum);
 
-    int save_file_fd = openat(objects_dir_fd, checksum, O_CREAT | O_WRONLY | O_TRUNC, 0774);
+    int save_file_fd = openat(objects_dir_fd, checksum, O_CREAT | O_WRONLY | O_TRUNC, DEFAULT_FILE_MODE);
     if(save_file_fd == -1) {
-        error_print("Object %s already exists", checksum);
-        defer(-1);
+        if (errno == EACCES)
+        {
+            debug_print("Object %s already exists", checksum);
+            defer(OBJECT_ALREADY_EXIST);
+        }
+        defer(FS_ERROR);
     }
     FILE* save_file = fdopen(save_file_fd, "w");
 
@@ -53,7 +158,7 @@ int write_object(struct object *obj)
     int res = compress_object(obj, compressed, &comp_size);
     if (res != Z_OK)
     {
-        defer(res);
+        defer(COMPRESSION_ERROR);
     }
     fwrite(compressed, comp_size, 1, save_file);
     free(compressed);
@@ -68,25 +173,29 @@ int read_object(char *checksum, struct object *obj)
 {
     if(!local_repo_exist())
     {
-        return -2;
+        return REPO_NOT_INITIALIZED;
     }
-    int result = 0;
+    int result = FS_OK;
 
     struct stat buffer;
-    if (stat(LOCAL_REPO"/objects", &buffer) != 0)
+    if (stat(OBJECTS_REPO, &buffer) != 0)
     {
         error_print("Object dir does not exist");
-        return -1;
+        return OBJECT_DOES_NOT_EXIST;
     }
 
-    DIR *objects_dir = opendir(LOCAL_REPO"/objects");
+    DIR *objects_dir = opendir(OBJECTS_REPO);
     int objects_dir_fd = dirfd(objects_dir);
 
     int save_file_fd = openat(objects_dir_fd, checksum, O_RDONLY, DEFAULT_FILE_MODE);    
     if (save_file_fd == -1)
     {
-        error_print("Object %s does not exist", checksum);
-        defer(-1);
+        if(errno == EACCES)
+        {    
+            error_print("Object %s does not exist", checksum);
+            defer(OBJECT_DOES_NOT_EXIST);
+        }
+        defer(FS_ERROR);
     }
     fstatat(objects_dir_fd, checksum, &buffer, 0);
     char* file_content = malloc(buffer.st_size);
@@ -96,9 +205,9 @@ int read_object(char *checksum, struct object *obj)
     fclose(save_file);
 
     int res = uncompress_object(obj, file_content, buffer.st_size);
-    if(res != 0)
+    if(res != Z_OK)
     {
-        defer(res);
+        defer(COMPRESSION_ERROR);
     }
     
     free(file_content);
@@ -110,12 +219,15 @@ defer:
 
 int main(void)
 {
-    struct object obj = {0};
-    obj.content = "Hello, world!\n";
-    obj.size = strlen(obj.content);
-    obj.object_type = "blob";
+    struct index index = {0};
+    load_index(&index);
 
-    return write_object(&obj);
+    // struct object obj = {0};
+    // obj.content = "Hello, world!\n";
+    // obj.size = strlen(obj.content);
+    // obj.object_type = "blob";
+
+    // return write_object(&obj);
 
     // read_object("af5626b4a114abcb82d63db7c8082c3c4756e51b", &obj);
 
@@ -124,5 +236,14 @@ int main(void)
     // debug_print("Content is %.*s", (int)obj.size, obj.content);
 
     // free_object(&obj);
-    // return 0;
+
+    add_to_index(&index, "src/fs.c");
+
+    dump_index(&index);
+
+    save_index(&index);
+
+    free_index(&index);
+
+    return 0;
 }
\ No newline at end of file
diff --git a/src/fs.h b/src/fs.h
index 249e271..d28898a 100644
--- a/src/fs.h
+++ b/src/fs.h
@@ -4,9 +4,23 @@
 #include "objects.h"
 
 #define LOCAL_REPO ".cgit"
+#define INDEX_FILE LOCAL_REPO"/index"
+#define OBJECTS_REPO LOCAL_REPO"/objects"
 #define DEFAULT_DIR_MODE 0755
 #define DEFAULT_FILE_MODE 0444
 
+#define FS_OK (0)
+#define FS_ERROR (-1)
+#define COMPRESSION_ERROR (-2)
+#define REPO_NOT_INITIALIZED (-10)
+#define OBJECT_ALREADY_EXIST (-20)
+#define OBJECT_DOES_NOT_EXIST (-21)
+#define FILE_NOT_FOUND (-22)
+#define ENTRY_NOT_FOUND (-23)
+
+int local_repo_exist();
+int index_exist();
+
 int write_object(struct object *obj);
 int read_object(char *checksum, struct object *obj);
 
diff --git a/src/index.c b/src/index.c
new file mode 100644
index 0000000..42c266f
--- /dev/null
+++ b/src/index.c
@@ -0,0 +1,133 @@
+#include <stdlib.h>
+#include <string.h>
+
+#include "index.h"
+#include "includes.h"
+#include "fs.h"
+
+void free_entry(struct entry *entry)
+{
+    if (entry->checksum != NULL)
+        free(entry->checksum);
+    
+    if (entry->filename != NULL)
+        free(entry->filename);
+
+}
+
+void free_index(struct index *index)
+{
+    struct entry *current = index->first_entry;
+    struct entry *next;
+    while(current != NULL)
+    {
+        free_entry(current);
+        next = current->next;
+        free(current);
+        current = next;   
+    }
+}
+
+struct entry *find_entry(struct index *index, char* filename)
+{
+    struct entry *current = index->first_entry;
+    for (int i = 0; i < index->entries_size; i ++)
+    {
+        if (strncmp(filename, current->filename, strlen(filename)) == 0) {
+            return current;
+        }
+        current = current->next;
+    }
+
+    return NULL;
+}
+
+int add_to_index(struct index *index, char *filename)
+{
+    if(!local_repo_exist() || !index_exist())
+    {
+        return REPO_NOT_INITIALIZED;
+    }
+    
+    int result = FS_OK;
+    int new = 0;
+
+    struct entry *entry = find_entry(index, filename);
+    if (entry == NULL)
+    {
+        new = 1;
+        entry = calloc(sizeof(struct entry), 1);
+    } else {
+        free_entry(entry);
+    }
+
+    struct object object = {0};
+    if (blob_from_file(filename, &object) != 0)
+    {
+        return FILE_NOT_FOUND;
+    }
+
+    entry->filename = calloc(sizeof(char), strlen(filename) + 1);
+    strncat(entry->filename, filename, strlen(filename));
+    entry->checksum = calloc(sizeof(char), DIGEST_LENGTH * 2 + 1);
+    hash_object(&object, entry->checksum);
+    int res = write_object(&object);
+    if (res != FS_OK && res != OBJECT_ALREADY_EXIST)
+    {
+        defer(FS_ERROR);
+    }
+    
+    if(new)
+    {
+        if(index->entries_size == 0)
+        {
+            index->first_entry = entry;
+            index->last_entry = entry;
+        } else
+        {
+            entry->previous = index->last_entry;
+            index->last_entry->next = entry;
+            index->last_entry = entry;
+        }
+        index->entries_size = index->entries_size + 1;
+    }
+
+defer:
+    free_object(&object);
+    return result;
+}
+
+int remove_from_index(struct index *index, char *filename)
+{
+    if (!local_repo_exist() || !index_exist())
+    {
+        return REPO_NOT_INITIALIZED;
+    }
+
+    struct entry *entry = find_entry(index, filename);
+    if (entry == NULL)
+    {
+        return ENTRY_NOT_FOUND;
+    }
+
+    if(index->first_entry == entry)
+    {
+        index->first_entry = entry->next;
+    } else 
+    {
+        entry->previous->next = entry->next;
+    }
+
+    if (index->last_entry == entry)
+    {
+        index->last_entry = entry->previous;
+    } else 
+    {
+        entry->next->previous = entry->previous;
+    }
+
+    index->entries_size = index->entries_size - 1;
+    free_entry(entry);
+    free(entry);
+    return FS_OK;
+}
\ No newline at end of file
diff --git a/src/index.h b/src/index.h
new file mode 100644
index 0000000..74f632e
--- /dev/null
+++ b/src/index.h
@@ -0,0 +1,28 @@
+#ifndef INDEX_H
+#define INDEX_H
+
+#include <stddef.h>
+
+// Index file should follow the format
+// number of entries\n
+// entry1\n
+// entry2\n
+// ...
+struct entry {
+    char *checksum;
+    char *filename;
+    struct entry *previous;
+    struct entry *next;
+};
+
+struct index {
+    size_t entries_size;
+    struct entry *first_entry;
+    struct entry *last_entry;
+};
+
+void free_index(struct index *index);
+int add_to_index(struct index *index, char *filename);
+int remove_from_index(struct index *index, char *filename);
+
+#endif // INDEX_H
\ No newline at end of file
diff --git a/src/objects.c b/src/objects.c
index 3467525..afb35fe 100644
--- a/src/objects.c
+++ b/src/objects.c
@@ -1,22 +1,16 @@
 #include <assert.h>
 #include <math.h>
 #include <openssl/sha.h>
+#include <sys/stat.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <zlib.h>
 
 #include "includes.h"
+#include "utils.h"
 #include "objects.h"
 
-int decimal_len(size_t size)
-{
-    if (size == 0)
-        return 1;
-
-    return floor(log10(size)) + 1;
-}
-
 size_t header_size(struct object *obj)
 {
     return strlen(obj->object_type) + 2 + decimal_len(obj->size);
@@ -51,7 +45,7 @@ int full_object(struct object *obj, char *buffer, size_t buffer_size)
     return 0;
 }
 
-void hash_object(struct object *obj, char* result)
+void hash_object(struct object *obj, char *result)
 {
     unsigned char md_buffer[DIGEST_LENGTH] = {0};
     size_t data_size = object_size(obj);
@@ -62,7 +56,7 @@ void hash_object(struct object *obj, char* result)
 
     for (int i = 0; i < DIGEST_LENGTH; i++)
     {
-        sprintf((result + 2 * i), "%.2x", md_buffer[i]);
+        sprintf((result + (2 * i)), "%.2x", md_buffer[i]);
     }
 
     free(data);
@@ -113,11 +107,27 @@ int compress_object(struct object *obj, char* compressed, uLongf *comp_size)
     return res;
 }
 
+int blob_from_file(char *filename, struct object *object)
+{
+    FILE* file = fopen(filename, "r");
+    if (file == NULL)
+        return -1;
+
+    struct stat file_info;
+    if (stat(filename, &file_info) != 0)
+        return -1;
+    
+    object->object_type = "blob";
+    object->size = file_info.st_size;
+    object->content = realloc(object->content, object->size);
+    fread(object->content, 1, object->size, file);
+    fclose(file);
+
+    return 0;
+}
+
 void free_object(struct object *obj)
 {
-    if (obj->object_type != NULL)
-        free(obj->object_type);
-
     if (obj->content != NULL)
         free(obj->content);
 }
diff --git a/src/objects.h b/src/objects.h
index 65a48e6..5023e53 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2,6 +2,7 @@
 #define OBJECTS_H 1
 
 #include <stddef.h>
+#include <zconf.h>
 
 #define DIGEST_LENGTH 20
 #define HEADER_MAX_SIZE 20
@@ -18,6 +19,7 @@ int full_object(struct object *obj, char* buffer, size_t buffer_size);
 int uncompress_object(struct object *obj, char* compressed, uLongf comp_size);
 int compress_object(struct object *obj, char* compressed, uLongf *comp_size);
 void hash_object(struct object *obj, char* result);
+int blob_from_file(char *filename, struct object *object);
 void free_object(struct object *obj);
 
 #endif // OBJECTS_H
diff --git a/src/utils.c b/src/utils.c
new file mode 100644
index 0000000..83b58af
--- /dev/null
+++ b/src/utils.c
@@ -0,0 +1,11 @@
+#include <math.h>
+
+#include "utils.h"
+
+int decimal_len(size_t size)
+{
+    if (size == 0)
+        return 1;
+
+    return floor(log10(size)) + 1;
+}
diff --git a/src/utils.h b/src/utils.h
new file mode 100644
index 0000000..e4ef1e2
--- /dev/null
+++ b/src/utils.h
@@ -0,0 +1,8 @@
+#ifndef UTILS_H
+#define UTILS_H 1
+
+#include <stddef.h>
+
+int decimal_len(size_t size);
+
+#endif // UTILS_H
\ No newline at end of file