diff --git a/main.go b/main.go
index ad8cb2b..6d59bd7 100644
--- a/main.go
+++ b/main.go
@@ -3,7 +3,6 @@ package main
 import (
 	"bytes"
 	"context"
-	"encoding/csv"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -98,7 +97,7 @@ func newHandlerGetAPIV1Messages(cfg Config) http.HandlerFunc {
 			return
 		}
 
-		writeJSON(w, map[string]any{"messages": messages})
+		encodeJSONResponse(w, map[string]any{"messages": messages})
 	}
 }
 
@@ -120,7 +119,7 @@ func newHandlerGetAPIV1Threads(cfg Config) http.HandlerFunc {
 			return
 		}
 
-		writeJSON(w, map[string]any{"threads": threads})
+		encodeJSONResponse(w, map[string]any{"threads": threads})
 	}
 }
 
@@ -138,7 +137,7 @@ func newHandlerGetAPIV1ThreadsThread(cfg Config) http.HandlerFunc {
 			return
 		}
 
-		writeJSON(w, map[string]any{"thread": map[string]any{"messages": messages}})
+		encodeJSONResponse(w, map[string]any{"thread": map[string]any{"messages": messages}})
 	}
 }
 
@@ -169,7 +168,7 @@ func handlerPostAPIV1EventsSlackInitialize(w http.ResponseWriter, r *http.Reques
 		return
 	}
 
-	writeJSON(w, map[string]any{"challenge": challenge.Challenge})
+	encodeJSONResponse(w, map[string]any{"challenge": challenge.Challenge})
 }
 
 func _newHandlerPostAPIV1EventsSlack(cfg Config) http.HandlerFunc {
@@ -245,14 +244,24 @@ func parseSince(s string) (time.Time, error) {
 	return time.Time{}, fmt.Errorf("failed to parse since=%q", s)
 }
 
-func writeJSON(w http.ResponseWriter, v interface{}) error {
+func encodeResponse(w http.ResponseWriter, r *http.Request, v interface{}) error {
+	if strings.Contains(r.Header.Get("Accept"), "text/csv") {
+		return encodeCSVResponse(w, v)
+	}
+	return encodeJSONResponse(w, v)
+}
+
+func encodeJSONResponse(w http.ResponseWriter, v interface{}) error {
 	return json.NewEncoder(w).Encode(v)
 }
 
-func writeCSV(w http.ResponseWriter, fields []string, values [][]string) error {
-	enc := csv.NewWriter(w)
-	if err := enc.Write(fields); err != nil {
-		return err
-	}
-	return enc.WriteAll(values)
+func encodeCSVResponse(w http.ResponseWriter, v interface{}) error {
+	return errors.New("not impl")
+	/*
+		enc := csv.NewWriter(w)
+		if err := enc.Write(fields); err != nil {
+			return err
+		}
+		return enc.WriteAll(values)
+	*/
 }