diff --git a/README.md b/README.md
index 7c9ba2f..4837cc6 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,41 @@ No breaking changes will be made to exported APIs before v2.0.0.
 
 ## 💡 Usage
 
+### Handler options
+
+```go
+type Config struct {
+	DefaultLevel     slog.Level
+	ClientErrorLevel slog.Level
+	ServerErrorLevel slog.Level
+
+	WithUserAgent      bool
+	WithRequestID      bool
+	WithRequestBody    bool
+	WithRequestHeader  bool
+	WithResponseBody   bool
+	WithResponseHeader bool
+	WithSpanID         bool
+	WithTraceID        bool
+
+	Filters []Filter
+}
+```
+
+Attributes will be injected in log payload.
+
+Other global parameters:
+
+```go
+sloggin.TraceIDKey = "trace-id"
+sloggin.SpanIDKey = "span-id"
+sloggin.RequestBodyMaxSize  = 64 * 1024 // 64KB
+sloggin.ResponseBodyMaxSize = 64 * 1024 // 64KB
+sloggin.HiddenRequestHeaders = map[string]struct{}{ ... }
+sloggin.HiddenResponseHeaders = map[string]struct{}{ ... }
+sloggin.RequestIDHeaderKey = "X-Request-Id"
+```
+
 ### Minimal
 
 ```go
diff --git a/middleware.go b/middleware.go
index 906fead..1747c4a 100644
--- a/middleware.go
+++ b/middleware.go
@@ -18,6 +18,9 @@ const (
 )
 
 var (
+	TraceIDKey = "trace-id"
+	SpanIDKey  = "span-id"
+
 	RequestBodyMaxSize  = 64 * 1024 // 64KB
 	ResponseBodyMaxSize = 64 * 1024 // 64KB
 
@@ -168,11 +171,11 @@ func NewWithConfig(logger *slog.Logger, config Config) gin.HandlerFunc {
 		// otel
 		if config.WithTraceID {
 			traceID := trace.SpanFromContext(c.Request.Context()).SpanContext().TraceID().String()
-			baseAttributes = append(baseAttributes, slog.String("trace-id", traceID))
+			baseAttributes = append(baseAttributes, slog.String(TraceIDKey, traceID))
 		}
 		if config.WithSpanID {
 			spanID := trace.SpanFromContext(c.Request.Context()).SpanContext().SpanID().String()
-			baseAttributes = append(baseAttributes, slog.String("span-id", spanID))
+			baseAttributes = append(baseAttributes, slog.String(SpanIDKey, spanID))
 		}
 
 		// request body