diff --git a/src/core/sappyou.c b/src/core/sappyou.c
index 4763b4f..4e24eb8 100644
--- a/src/core/sappyou.c
+++ b/src/core/sappyou.c
@@ -34,14 +34,12 @@ int sappyou_free(Sappyou *sappyou) {
 
 int sappyou_load(Sappyou *sappyou) {
     if (sappyou->file == NULL) {
-        fprintf(stderr, "Failed to load sappyou: input file not specified\n");
         return 1;
     }
     uint16_t signature[4];
     rewind(sappyou->file);
     fread(signature, 2, 4, sappyou->file);
     if (memcmp(signature, SAPPYOU_SIG, 8) != 0) {
-        fprintf(stderr, "Failed to load sappyou: invalid signature\n");
         return 1;
     }
     fread(&sappyou->created_ts, 8, 1, sappyou->file);
@@ -69,7 +67,6 @@ int sappyou_load(Sappyou *sappyou) {
 
 int sappyou_save(Sappyou *sappyou) {
     if (sappyou->file == NULL) {
-        fprintf(stderr, "Failed to save sappyou: output file not specified\n");
         return 1;
     }
     rewind(sappyou->file);
@@ -99,7 +96,6 @@ int sappyou_save(Sappyou *sappyou) {
 int sappyou_open(Sappyou *sappyou, const char *path) {
     sappyou->file = fopen(path, "r+b");
     if (sappyou->file == NULL) {
-        fprintf(stderr, "Failed to open sappyou: failed to open file '%s'\n", path);
         return 1;
     }
     return sappyou_load(sappyou);
@@ -108,7 +104,6 @@ int sappyou_open(Sappyou *sappyou, const char *path) {
 int sappyou_dump(Sappyou *sappyou, const char *path) {
     sappyou->file = fopen(path, "w+b");
     if (sappyou->file == NULL) {
-        fprintf(stderr, "Failed to dump sappyou: failed to write to file '%s'\n", path);
         return 1;
     }
     return sappyou_save(sappyou);
@@ -116,7 +111,6 @@ int sappyou_dump(Sappyou *sappyou, const char *path) {
 
 int tanzaku_add(Sappyou *sappyou, const char *name, const char *description) {
     if (sappyou->size == -1 && sappyou->hole_cnt == 0) {
-        fprintf(stderr, "Failed to add tanzaku: sappyou is full\n");
         return 1;
     }
     Tanzaku newbie;
@@ -148,11 +142,9 @@ int tanzaku_add(Sappyou *sappyou, const char *name, const char *description) {
 
 int tanzaku_rem(Sappyou *sappyou, uint64_t tanzaku_id) {
     if (tanzaku_id == HOLE_ID) {
-        fprintf(stderr, "Failed to remove tanzaku: got hole ID\n");
         return 1;
     }
     if (tanzaku_id >= sappyou->size) {
-        fprintf(stderr, "Failed to remove tanzaku: too big ID\n");
         return 1;
     }
     if (sappyou->database[tanzaku_id].id == HOLE_ID) {
diff --git a/src/core/sasahyou.c b/src/core/sasahyou.c
index aa049a1..1172337 100644
--- a/src/core/sasahyou.c
+++ b/src/core/sasahyou.c
@@ -35,14 +35,12 @@ int sasahyou_free(Sasahyou *sasahyou) {
 
 int sasahyou_load(Sasahyou *sasahyou) {
     if (sasahyou->file == NULL) {
-        fprintf(stderr, "Failed to load sasahyou: input file not specified\n");
         return 1;
     }
     uint16_t signature[4];
     rewind(sasahyou->file);
     fread(signature, 2, 4, sasahyou->file);
     if (memcmp(signature, SASAHYOU_SIG, 8) != 0) {
-        fprintf(stderr, "Failed to load sasahyou: invalid signature\n");
         return 1;
     }
     fread(&sasahyou->created_ts, 8, 1, sasahyou->file);
@@ -68,7 +66,6 @@ int sasahyou_load(Sasahyou *sasahyou) {
 
 int sasahyou_save(Sasahyou *sasahyou) {
     if (sasahyou->file == NULL) {
-        fprintf(stderr, "Failed to save sasahyou: output file not specified\n");
         return 1;
     }
     rewind(sasahyou->file);
@@ -95,7 +92,6 @@ int sasahyou_save(Sasahyou *sasahyou) {
 int sasahyou_open(Sasahyou *sasahyou, const char *path) {
     sasahyou->file = fopen(path, "r+b");
     if (sasahyou->file == NULL) {
-        fprintf(stderr, "Failed to open sasahyou: failed to open file '%s'\n", path);
         return 1;
     }
     return sasahyou_load(sasahyou);
@@ -104,7 +100,6 @@ int sasahyou_open(Sasahyou *sasahyou, const char *path) {
 int sasahyou_dump(Sasahyou *sasahyou, const char *path) {
     sasahyou->file = fopen(path, "w+b");
     if (sasahyou->file == NULL) {
-        fprintf(stderr, "Failed to dump sasahyou: failed to write to file '%s'\n", path);
         return 1;
     }
     return sasahyou_save(sasahyou);
@@ -112,7 +107,6 @@ int sasahyou_dump(Sasahyou *sasahyou, const char *path) {
 
 int sasa_add(Sasahyou *sasahyou, const char *path) {
     if (sasahyou->size == -1 && sasahyou->hole_cnt == 0) {
-        fprintf(stderr, "Failed to add sasa: sasahyou is full\n");
         return 1;
     }
     Sasa newbie;
@@ -139,11 +133,9 @@ int sasa_add(Sasahyou *sasahyou, const char *path) {
 
 int sasa_rem(Sasahyou *sasahyou, uint64_t sasa_id) {
     if (sasa_id == HOLE_ID) {
-        fprintf(stderr, "Failed to remove sasa: got hole ID\n");
         return 1;
     }
     if (sasa_id >= sasahyou->size) {
-        fprintf(stderr, "Failed to remove sasa: too big ID\n");
         return 1;
     }
     if (sasahyou->database[sasa_id].id == HOLE_ID) {
diff --git a/src/core/shoppyou.c b/src/core/shoppyou.c
index b526cf0..c9de915 100644
--- a/src/core/shoppyou.c
+++ b/src/core/shoppyou.c
@@ -31,14 +31,12 @@ int shoppyou_free(Shoppyou *shoppyou) {
 
 int shoppyou_load(Shoppyou *shoppyou) {
     if (shoppyou->file == NULL) {
-        fprintf(stderr, "Failed to load shoppyou: input file not specified\n");
         return 1;
     }
     uint16_t signature[4];
     rewind(shoppyou->file);
     fread(signature, 2, 4, shoppyou->file);
     if (memcmp(signature, SHOPPYOU_SIG, 8) != 0) {
-        fprintf(stderr, "Failed to load shoppyou: invalid signature\n");
         return 1;
     }
     fread(&shoppyou->created_ts, 8, 1, shoppyou->file);
@@ -57,7 +55,6 @@ int shoppyou_load(Shoppyou *shoppyou) {
 
 int shoppyou_save(Shoppyou *shoppyou) {
     if (shoppyou->file == NULL) {
-        fprintf(stderr, "Failed to save shoppyou: output file not specified\n");
         return 1;
     }
     rewind(shoppyou->file);
@@ -81,7 +78,6 @@ int shoppyou_save(Shoppyou *shoppyou) {
 int shoppyou_open(Shoppyou *shoppyou, const char *path) {
     shoppyou->file = fopen(path, "r+b");
     if (shoppyou->file == NULL) {
-        fprintf(stderr, "Failed to open shoppyou: failed to open file '%s'\n", path);
         return 1;
     }
     shoppyou->holes = NULL;
@@ -91,7 +87,6 @@ int shoppyou_open(Shoppyou *shoppyou, const char *path) {
 int shoppyou_dump(Shoppyou *shoppyou, const char *path) {
     shoppyou->file = fopen(path, "w+b");
     if (shoppyou->file == NULL) {
-        fprintf(stderr, "Failed to dump shoppyou: failed to write to file '%s'\n", path);
         return 1;
     }
     return shoppyou_save(shoppyou);
@@ -99,11 +94,9 @@ int shoppyou_dump(Shoppyou *shoppyou, const char *path) {
 
 int kazari_add(Shoppyou *shoppyou, uint64_t sasa_id, uint64_t tanzaku_id) {
     if (sasa_id == HOLE_ID || tanzaku_id == HOLE_ID) {
-        fprintf(stderr, "Failed to add kazari: got hole ID\n");
         return 1;
     }
     if (shoppyou->size == -1 && shoppyou->hole_cnt == 0) {
-        fprintf(stderr, "Failed to add kazari: shoppyou is full\n");
         return 1;
     }
     Kazari newbie;
@@ -125,7 +118,6 @@ int kazari_add(Shoppyou *shoppyou, uint64_t sasa_id, uint64_t tanzaku_id) {
 
 int kazari_rem(Shoppyou *shoppyou, uint64_t sasa_id, uint64_t tanzaku_id) {
     if (sasa_id == HOLE_ID || tanzaku_id == HOLE_ID) {
-        fprintf(stderr, "Failed to remove kazari: got hole ID\n");
         return 1;
     }
     for (uint64_t i = 0; i < shoppyou->size; i++) {