diff --git a/audit/logging.go b/audit/logging.go
new file mode 100644
index 0000000..ab6af47
--- /dev/null
+++ b/audit/logging.go
@@ -0,0 +1,88 @@
+package audit
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"path"
+	"time"
+
+	config "codeberg.org/vnpower/pixivfe/v2/config"
+)
+
+const DevDir_Response = "/tmp/pixivfe-dev/resp"
+
+var optionSaveResponse bool
+
+func Init(saveResponse bool) error {
+	optionSaveResponse = saveResponse
+	if optionSaveResponse {
+		return os.MkdirAll(DevDir_Response, 0o700)
+	} else {
+		return nil
+	}
+}
+
+type ServerPerformance struct {
+	StartTime   time.Time
+	EndTime     time.Time
+	RemoteAddr  string
+	Method      string
+	Path        string
+	Status      int
+	Error       error
+	SkipLogging bool
+}
+
+type APIPerformance struct {
+	StartTime        time.Time
+	EndTime          time.Time
+	Response         *http.Response
+	Error            error
+	Method           string
+	Url              string
+	Token            string
+	Body             string
+	ResponseFilename string
+}
+
+func LogServerRoundTrip(perf ServerPerformance) {
+	if perf.Error != nil {
+		log.Printf("Internal Server Error: %s", perf.Error)
+	}
+
+	if !perf.SkipLogging {
+		// todo: log.Printf("%v +%v %v %v %v %v %v", time, latency, ip, method, path, status, err)
+	}
+}
+
+func LogAPIRoundTrip(perf APIPerformance) {
+	if perf.Response != nil {
+		if perf.Body != "" && optionSaveResponse {
+			var err error
+			perf.ResponseFilename, err = writeResponseBodyToFile(perf.Body)
+			if err != nil {
+				log.Println("When saving response to file: ", err)
+			}
+		}
+		if !(300 > perf.Response.StatusCode && perf.Response.StatusCode >= 200) {
+			log.Println("(WARN) non-2xx response from pixiv:")
+		}
+	}
+	// structured logging
+	if config.GlobalServerConfig.InDevelopment {
+		// todo
+	} else {
+		// todo
+	}
+}
+
+func writeResponseBodyToFile(body string) (string, error) {
+	filename := path.Join(DevDir_Response, time.Now().UTC().Format(time.RFC3339Nano))
+	err := os.WriteFile(filename, []byte(body), 0o600)
+	if err != nil {
+		return "", err
+	}
+	return filename, nil
+}
diff --git a/audit/trace_route.go b/audit/trace_route.go
deleted file mode 100644
index 1d15d92..0000000
--- a/audit/trace_route.go
+++ /dev/null
@@ -1,27 +0,0 @@
-package audit
-
-import (
-	"log"
-	"time"
-)
-
-type RoutePerf struct {
-	StartTime   time.Time
-	EndTime     time.Time
-	RemoteAddr  string
-	Method      string
-	Path        string
-	Status      int
-	Err         error
-	SkipLogging bool
-}
-
-func TraceRoute(data RoutePerf) {
-	if data.Err != nil {
-		log.Printf("Internal Server Error: %s", data.Err)
-	}
-
-	if !data.SkipLogging {
-		// todo: log.Printf("%v +%v %v %v %v %v %v", time, latency, ip, method, path, status, err)
-	}
-}
diff --git a/audit/trace_webapi.go b/audit/trace_webapi.go
deleted file mode 100644
index c72d324..0000000
--- a/audit/trace_webapi.go
+++ /dev/null
@@ -1,59 +0,0 @@
-package audit
-
-import (
-	"fmt"
-	"log"
-	"net/http"
-	"os"
-	"path"
-	"time"
-
-	config "codeberg.org/vnpower/pixivfe/v2/config"
-)
-
-const DevDir_Response = "/tmp/pixivfe-dev/resp"
-
-var optionSaveResponse bool
-
-func Init(saveResponse bool) error {
-	optionSaveResponse = saveResponse
-	if optionSaveResponse {
-		return os.MkdirAll(DevDir_Response, 0o700)
-	} else {
-		return nil
-	}
-}
-
-func LogAPIRoundTrip(resp *http.Response, err error, method, url, token, body string, start_time, end_time time.Time) {
-	if config.GlobalServerConfig.InDevelopment {
-		errs := ""
-		if err != nil {
-			errs = fmt.Sprintf("ERR %v", err)
-		}
-		if resp != nil {
-			filename := ""
-			if body != "" && optionSaveResponse {
-				var err error
-				filename, err = writeResponseBodyToFile(body)
-				if err != nil {
-					log.Println(err)
-				}
-			}
-			if !(300 > resp.StatusCode && resp.StatusCode >= 200) {
-				log.Println("(WARN) non-2xx response from pixiv:")
-			}
-			log.Println("->", method, url, "->", resp.StatusCode, filename, errs)
-		} else {
-			log.Println("->", method, url, errs)
-		}
-	}
-}
-
-func writeResponseBodyToFile(body string) (string, error) {
-	filename := path.Join(DevDir_Response, time.Now().UTC().Format(time.RFC3339Nano))
-	err := os.WriteFile(filename, []byte(body), 0o600)
-	if err != nil {
-		return "", err
-	}
-	return filename, nil
-}
diff --git a/core/requests.go b/core/requests.go
index 3e285f3..7831f38 100644
--- a/core/requests.go
+++ b/core/requests.go
@@ -25,7 +25,7 @@ func API_GET(context context.Context, url string, token string) (SimpleHTTPRespo
 	start_time := time.Now()
 	res, resp, err := _API_GET(context, url, token)
 	end_time := time.Now()
-	audit.LogAPIRoundTrip(resp, err, "GET", url, token, res.Body, start_time, end_time)
+	audit.LogAPIRoundTrip(audit.APIPerformance{resp, err, "GET", url, token, res.Body, start_time, end_time})
 	if err != nil {
 		return SimpleHTTPResponse{}, fmt.Errorf("While GET %s: %w", url, err)
 	}
@@ -102,7 +102,7 @@ func API_POST(r *http.Request, url, payload, token, csrf string, isJSON bool) er
 	start_time := time.Now()
 	resp, err := _API_POST(r, url, payload, token, csrf, isJSON)
 	end_time := time.Now()
-	audit.LogAPIRoundTrip(resp, err, "POST", url, token, "", start_time, end_time)
+	audit.LogAPIRoundTrip(audit.APIPerformance{Response: resp, Error: err, Method: "POST", Url: url, Token: token, Body: "", StartTime: start_time, EndTime: end_time})
 	if err != nil {
 		return fmt.Errorf("While POST %s: %w", url, err)
 	}
diff --git a/handlers/logger.go b/handlers/logger.go
index d6f3652..e7eaf6f 100644
--- a/handlers/logger.go
+++ b/handlers/logger.go
@@ -44,14 +44,14 @@ func LogRequest(f func(w http.ResponseWriter, r *http.Request)) func(w http.Resp
 
 		end_time := time.Now()
 
-		audit.TraceRoute(audit.RoutePerf{
+		audit.LogServerRoundTrip(audit.ServerPerformance{
 			StartTime:   start_time,
 			EndTime:     end_time,
 			RemoteAddr:  r.RemoteAddr,
 			Method:      r.Method,
 			Path:        r.URL.Path,
 			Status:      w.statusCode,
-			Err:         GetUserContext(r).Err,
+			Error:         GetUserContext(r).Err,
 			SkipLogging: CanRequestSkipLogger(r),
 		})
 	}