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

api/types.go

@@ -90,6 +90,10 @@ type GenerateRequest struct {
 	// (request that thinking _not_ be used) and unset (use the old behavior
 	// before this option was introduced)
 	Think *ThinkValue `json:"think,omitempty"`
+
+	// DebugRenderOnly is a debug option that, when set to true, returns the rendered
+	// template instead of calling the model.
+	DebugRenderOnly bool `json:"_debug_render_only,omitempty"`
 }
 
 // ChatRequest describes a request sent by [Client.Chat].
@@ -120,6 +124,10 @@ type ChatRequest struct {
 	// responding. Can be a boolean (true/false) or a string ("high", "medium", "low")
 	// for supported models.
 	Think *ThinkValue `json:"think,omitempty"`
+
+	// DebugRenderOnly is a debug option that, when set to true, returns the rendered
+	// template instead of calling the model.
+	DebugRenderOnly bool `json:"_debug_render_only,omitempty"`
 }
 
 type Tools []Tool
@@ -308,6 +316,19 @@ type ChatResponse struct {
 	Metrics
 }
 
+// DebugInfo contains debug information for template rendering
+type DebugInfo struct {
+	RenderedTemplate string `json:"rendered_template"`
+	ImageCount       int    `json:"image_count,omitempty"`
+}
+
+// DebugTemplateResponse is returned when _debug_render_only is set to true
+type DebugTemplateResponse struct {
+	Model     string    `json:"model"`
+	CreatedAt time.Time `json:"created_at"`
+	DebugInfo DebugInfo `json:"_debug_info"`
+}
+
 type Metrics struct {
 	TotalDuration      time.Duration `json:"total_duration,omitempty"`
 	LoadDuration       time.Duration `json:"load_duration,omitempty"`

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

server/routes_debug_test.go

@@ -0,0 +1,413 @@
+package server
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/ollama/ollama/api"
+	"github.com/ollama/ollama/discover"
+	"github.com/ollama/ollama/fs/ggml"
+	"github.com/ollama/ollama/llm"
+)
+
+func TestGenerateDebugRenderOnly(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	mock := mockRunner{
+		CompletionResponse: llm.CompletionResponse{
+			Done:               true,
+			DoneReason:         llm.DoneReasonStop,
+			PromptEvalCount:    1,
+			PromptEvalDuration: 1,
+			EvalCount:          1,
+			EvalDuration:       1,
+		},
+	}
+
+	s := Server{
+		sched: &Scheduler{
+			pendingReqCh:  make(chan *LlmRequest, 1),
+			finishedReqCh: make(chan *LlmRequest, 1),
+			expiredCh:     make(chan *runnerRef, 1),
+			unloadedCh:    make(chan any, 1),
+			loaded:        make(map[string]*runnerRef),
+			newServerFn:   newMockServer(&mock),
+			getGpuFn:      discover.GetGPUInfo,
+			getCpuFn:      discover.GetCPUInfo,
+			reschedDelay:  250 * time.Millisecond,
+			loadFn: func(req *LlmRequest, _ *ggml.GGML, _ discover.GpuInfoList, _ bool) bool {
+				// add small delay to simulate loading
+				time.Sleep(time.Millisecond)
+				req.successCh <- &runnerRef{
+					llama: &mock,
+				}
+				return false
+			},
+		},
+	}
+
+	go s.sched.Run(t.Context())
+
+	// Create a test model
+	stream := false
+	_, digest := createBinFile(t, ggml.KV{
+		"general.architecture":          "llama",
+		"llama.block_count":             uint32(1),
+		"llama.context_length":          uint32(8192),
+		"llama.embedding_length":        uint32(4096),
+		"llama.attention.head_count":    uint32(32),
+		"llama.attention.head_count_kv": uint32(8),
+		"tokenizer.ggml.tokens":         []string{""},
+		"tokenizer.ggml.scores":         []float32{0},
+		"tokenizer.ggml.token_type":     []int32{0},
+	}, []*ggml.Tensor{
+		{Name: "token_embd.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_norm.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.ffn_down.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.ffn_gate.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.ffn_up.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.ffn_norm.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_k.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_output.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_q.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_v.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "output.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+	})
+
+	w := createRequest(t, s.CreateHandler, api.CreateRequest{
+		Model:    "test-model",
+		Files:    map[string]string{"file.gguf": digest},
+		Template: "{{ .Prompt }}",
+		Stream:   &stream,
+	})
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected status 200, got %d", w.Code)
+	}
+
+	tests := []struct {
+		name            string
+		request         api.GenerateRequest
+		expectDebug     bool
+		expectTemplate  string
+		expectNumImages int
+	}{
+		{
+			name: "debug render only enabled",
+			request: api.GenerateRequest{
+				Model:           "test-model",
+				Prompt:          "Hello, world!",
+				DebugRenderOnly: true,
+			},
+			expectDebug:    true,
+			expectTemplate: "Hello, world!",
+		},
+		{
+			name: "debug render only disabled",
+			request: api.GenerateRequest{
+				Model:           "test-model",
+				Prompt:          "Hello, world!",
+				DebugRenderOnly: false,
+			},
+			expectDebug: false,
+		},
+		{
+			name: "debug render only with system prompt",
+			request: api.GenerateRequest{
+				Model:           "test-model",
+				Prompt:          "User question",
+				System:          "You are a helpful assistant",
+				DebugRenderOnly: true,
+			},
+			expectDebug:    true,
+			expectTemplate: "User question",
+		},
+		{
+			name: "debug render only with template",
+			request: api.GenerateRequest{
+				Model:           "test-model",
+				Prompt:          "Hello",
+				Template:        "PROMPT: {{ .Prompt }}",
+				DebugRenderOnly: true,
+			},
+			expectDebug:    true,
+			expectTemplate: "PROMPT: Hello",
+		},
+		{
+			name: "debug render only with images",
+			request: api.GenerateRequest{
+				Model:           "test-model",
+				Prompt:          "Describe this image",
+				Images:          []api.ImageData{[]byte("fake-image-data")},
+				DebugRenderOnly: true,
+			},
+			expectDebug:     true,
+			expectTemplate:  "[img-0]\n\nDescribe this image",
+			expectNumImages: 1,
+		},
+		{
+			name: "debug render only with raw mode",
+			request: api.GenerateRequest{
+				Model:           "test-model",
+				Prompt:          "Raw prompt text",
+				Raw:             true,
+				DebugRenderOnly: true,
+			},
+			expectDebug:    true,
+			expectTemplate: "Raw prompt text",
+		},
+	}
+
+	for _, tt := range tests {
+		// Test both with and without streaming
+		streamValues := []bool{false, true}
+		for _, stream := range streamValues {
+			streamSuffix := ""
+			if stream {
+				streamSuffix = " (streaming)"
+			}
+			t.Run(tt.name+streamSuffix, func(t *testing.T) {
+				req := tt.request
+				req.Stream = &stream
+				w := createRequest(t, s.GenerateHandler, req)
+
+				if tt.expectDebug {
+					if w.Code != http.StatusOK {
+						t.Errorf("expected status %d, got %d, body: %s", http.StatusOK, w.Code, w.Body.String())
+					}
+
+					var response api.DebugTemplateResponse
+					if err := json.Unmarshal(w.Body.Bytes(), &response); err != nil {
+						t.Fatalf("failed to unmarshal response: %v", err)
+					}
+
+					if response.Model != tt.request.Model {
+						t.Errorf("expected model %s, got %s", tt.request.Model, response.Model)
+					}
+
+					if tt.expectTemplate != "" && response.DebugInfo.RenderedTemplate != tt.expectTemplate {
+						t.Errorf("expected template %q, got %q", tt.expectTemplate, response.DebugInfo.RenderedTemplate)
+					}
+
+					if tt.expectNumImages > 0 && response.DebugInfo.ImageCount != tt.expectNumImages {
+						t.Errorf("expected image count %d, got %d", tt.expectNumImages, response.DebugInfo.ImageCount)
+					}
+				} else {
+					// When debug is disabled, it should attempt normal processing
+					if w.Code != http.StatusOK {
+						t.Errorf("expected status %d, got %d", http.StatusOK, w.Code)
+					}
+				}
+			})
+		}
+	}
+}
+
+func TestChatDebugRenderOnly(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	mock := mockRunner{
+		CompletionResponse: llm.CompletionResponse{
+			Done:               true,
+			DoneReason:         llm.DoneReasonStop,
+			PromptEvalCount:    1,
+			PromptEvalDuration: 1,
+			EvalCount:          1,
+			EvalDuration:       1,
+		},
+	}
+
+	s := Server{
+		sched: &Scheduler{
+			pendingReqCh:  make(chan *LlmRequest, 1),
+			finishedReqCh: make(chan *LlmRequest, 1),
+			expiredCh:     make(chan *runnerRef, 1),
+			unloadedCh:    make(chan any, 1),
+			loaded:        make(map[string]*runnerRef),
+			newServerFn:   newMockServer(&mock),
+			getGpuFn:      discover.GetGPUInfo,
+			getCpuFn:      discover.GetCPUInfo,
+			reschedDelay:  250 * time.Millisecond,
+			loadFn: func(req *LlmRequest, _ *ggml.GGML, _ discover.GpuInfoList, _ bool) bool {
+				// add small delay to simulate loading
+				time.Sleep(time.Millisecond)
+				req.successCh <- &runnerRef{
+					llama: &mock,
+				}
+				return false
+			},
+		},
+	}
+
+	go s.sched.Run(t.Context())
+
+	// Create a test model
+	stream := false
+	_, digest := createBinFile(t, ggml.KV{
+		"general.architecture":          "llama",
+		"llama.block_count":             uint32(1),
+		"llama.context_length":          uint32(8192),
+		"llama.embedding_length":        uint32(4096),
+		"llama.attention.head_count":    uint32(32),
+		"llama.attention.head_count_kv": uint32(8),
+		"tokenizer.ggml.tokens":         []string{""},
+		"tokenizer.ggml.scores":         []float32{0},
+		"tokenizer.ggml.token_type":     []int32{0},
+	}, []*ggml.Tensor{
+		{Name: "token_embd.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_norm.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.ffn_down.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.ffn_gate.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.ffn_up.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.ffn_norm.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_k.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_output.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_q.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "blk.0.attn_v.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+		{Name: "output.weight", Shape: []uint64{1}, WriterTo: bytes.NewReader(make([]byte, 4))},
+	})
+
+	w := createRequest(t, s.CreateHandler, api.CreateRequest{
+		Model:    "test-model",
+		Files:    map[string]string{"file.gguf": digest},
+		Template: "{{ if .Tools }}{{ .Tools }}{{ end }}{{ range .Messages }}{{ .Role }}: {{ .Content }}\n{{ end }}",
+		Stream:   &stream,
+	})
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected status 200, got %d", w.Code)
+	}
+
+	tests := []struct {
+		name            string
+		request         api.ChatRequest
+		expectDebug     bool
+		expectTemplate  string
+		expectNumImages int
+	}{
+		{
+			name: "chat debug render only enabled",
+			request: api.ChatRequest{
+				Model: "test-model",
+				Messages: []api.Message{
+					{Role: "system", Content: "You are a helpful assistant"},
+					{Role: "user", Content: "Hello"},
+				},
+				DebugRenderOnly: true,
+			},
+			expectDebug:    true,
+			expectTemplate: "system: You are a helpful assistant\nuser: Hello\n",
+		},
+		{
+			name: "chat debug render only disabled",
+			request: api.ChatRequest{
+				Model: "test-model",
+				Messages: []api.Message{
+					{Role: "user", Content: "Hello"},
+				},
+				DebugRenderOnly: false,
+			},
+			expectDebug: false,
+		},
+		{
+			name: "chat debug with assistant message",
+			request: api.ChatRequest{
+				Model: "test-model",
+				Messages: []api.Message{
+					{Role: "user", Content: "Hello"},
+					{Role: "assistant", Content: "Hi there!"},
+					{Role: "user", Content: "How are you?"},
+				},
+				DebugRenderOnly: true,
+			},
+			expectDebug:    true,
+			expectTemplate: "user: Hello\nassistant: Hi there!\nuser: How are you?\n",
+		},
+		{
+			name: "chat debug with images",
+			request: api.ChatRequest{
+				Model: "test-model",
+				Messages: []api.Message{
+					{
+						Role:    "user",
+						Content: "What's in this image?",
+						Images:  []api.ImageData{[]byte("fake-image-data")},
+					},
+				},
+				DebugRenderOnly: true,
+			},
+			expectDebug:     true,
+			expectTemplate:  "user: [img-0]What's in this image?\n",
+			expectNumImages: 1,
+		},
+		{
+			name: "chat debug with tools",
+			request: api.ChatRequest{
+				Model: "test-model",
+				Messages: []api.Message{
+					{Role: "user", Content: "Get the weather"},
+				},
+				Tools: api.Tools{
+					{
+						Type: "function",
+						Function: api.ToolFunction{
+							Name:        "get_weather",
+							Description: "Get weather information",
+						},
+					},
+				},
+				DebugRenderOnly: true,
+			},
+			expectDebug:    true,
+			expectTemplate: "[{\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"description\":\"Get weather information\",\"parameters\":{\"type\":\"\",\"required\":null,\"properties\":null}}}]user: Get the weather\n",
+		},
+	}
+
+	for _, tt := range tests {
+		// Test both with and without streaming
+		streamValues := []bool{false, true}
+		for _, stream := range streamValues {
+			streamSuffix := ""
+			if stream {
+				streamSuffix = " (streaming)"
+			}
+			t.Run(tt.name+streamSuffix, func(t *testing.T) {
+				req := tt.request
+				req.Stream = &stream
+				w := createRequest(t, s.ChatHandler, req)
+
+				if tt.expectDebug {
+					if w.Code != http.StatusOK {
+						t.Errorf("expected status %d, got %d, body: %s", http.StatusOK, w.Code, w.Body.String())
+					}
+
+					var response api.DebugTemplateResponse
+					if err := json.Unmarshal(w.Body.Bytes(), &response); err != nil {
+						t.Fatalf("failed to unmarshal response: %v", err)
+					}
+
+					if response.Model != tt.request.Model {
+						t.Errorf("expected model %s, got %s", tt.request.Model, response.Model)
+					}
+
+					if tt.expectTemplate != "" && response.DebugInfo.RenderedTemplate != tt.expectTemplate {
+						t.Errorf("expected template %q, got %q", tt.expectTemplate, response.DebugInfo.RenderedTemplate)
+					}
+
+					if tt.expectNumImages > 0 && response.DebugInfo.ImageCount != tt.expectNumImages {
+						t.Errorf("expected image count %d, got %d", tt.expectNumImages, response.DebugInfo.ImageCount)
+					}
+				} else {
+					// When debug is disabled, it should attempt normal processing
+					if w.Code != http.StatusOK {
+						t.Errorf("expected status %d, got %d", http.StatusOK, w.Code)
+					}
+				}
+			})
+		}
+	}
+}