server: add debug option for printing out prompt instead of calling model

server/routes.go

@@ -314,6 +314,19 @@ func (s *Server) GenerateHandler(c *gin.Context) {
 		prompt = b.String()
 	}
 
+	// If debug mode is enabled, return the rendered template instead of calling the model
+	if req.DebugRenderOnly {
+		c.JSON(http.StatusOK, api.DebugTemplateResponse{
+			Model:     req.Model,
+			CreatedAt: time.Now().UTC(),
+			DebugInfo: api.DebugInfo{
+				RenderedTemplate: prompt,
+				ImageCount:       len(images),
+			},
+		})
+		return
+	}
+
 	var thinkingState *thinking.Parser
 	if !useHarmony {
 		openingTag, closingTag := thinking.InferTags(m.Template.Template)
@@ -1597,6 +1610,19 @@ func (s *Server) ChatHandler(c *gin.Context) {
 		return
 	}
 
+	// If debug mode is enabled, return the rendered template instead of calling the model
+	if req.DebugRenderOnly {
+		c.JSON(http.StatusOK, api.DebugTemplateResponse{
+			Model:     req.Model,
+			CreatedAt: time.Now().UTC(),
+			DebugInfo: api.DebugInfo{
+				RenderedTemplate: prompt,
+				ImageCount:       len(images),
+			},
+		})
+		return
+	}
+
 	useHarmony := shouldUseHarmony(*m)
 
 	// Validate Think value: string values currently only allowed for gptoss models