parsers/renderers: functiongemma (#13521)

convert/tokenizer_spm.go

@@ -49,7 +49,8 @@ func parseSentencePiece(fsys fs.FS) (*Vocabulary, error) {
 			tt := int32(sentencepiece.ModelProto_SentencePiece_NORMAL)
 
 			// temporary fix to handle gemma3 broken configs
-			if slices.Contains([]string{"<end_of_turn>", "<start_of_turn>"}, piece.GetPiece()) {
+			// TODO(parthsareen): allow reading of tokenizer.json to allow managing special tokens when using spm
+			if slices.Contains([]string{"<end_of_turn>", "<start_of_turn>", "<start_function_declaration>", "<end_function_declaration>", "<start_function_call>", "<end_function_call>", "<start_function_response>", "<end_function_response>", "<escape>"}, piece.GetPiece()) {
 				tt = int32(sentencepiece.ModelProto_SentencePiece_CONTROL)
 			}
 

model/parsers/functiongemma.go

+package parsers
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/ollama/ollama/api"
+)
+
+type FunctionGemmaParserState int
+
+const (
+	FunctionGemmaCollectingContent FunctionGemmaParserState = iota
+	FunctionGemmaCollectingToolCalls
+)
+
+const (
+	functionGemmaFunctionCallOpen  = "<start_function_call>"
+	functionGemmaFunctionCallClose = "<end_function_call>"
+)
+
+// This format uses <start_function_call>call:name{args}<end_function_call> for tool calls.
+type FunctionGemmaParser struct {
+	state  FunctionGemmaParserState
+	buffer strings.Builder
+	tools  []api.Tool
+}
+
+func (p *FunctionGemmaParser) HasToolSupport() bool     { return true }
+func (p *FunctionGemmaParser) HasThinkingSupport() bool { return false }
+
+func (p *FunctionGemmaParser) Init(tools []api.Tool, lastMessage *api.Message, thinkValue *api.ThinkValue) []api.Tool {
+	p.tools = tools
+	p.state = FunctionGemmaCollectingContent
+	return tools
+}
+
+type functionGemmaEvent interface {
+	isFunctionGemmaEvent()
+}
+
+type FunctionGemmaEventContent struct {
+	content string
+}
+
+type functionGemmaEventToolCall struct {
+	toolCall api.ToolCall
+}
+
+func (FunctionGemmaEventContent) isFunctionGemmaEvent()  {}
+func (functionGemmaEventToolCall) isFunctionGemmaEvent() {}
+
+func (p *FunctionGemmaParser) Add(s string, done bool) (content string, thinking string, calls []api.ToolCall, err error) {
+	p.buffer.WriteString(s)
+	events := p.parseEvents()
+
+	var toolCalls []api.ToolCall
+	var contentSb strings.Builder
+	for _, event := range events {
+		switch event := event.(type) {
+		case functionGemmaEventToolCall:
+			toolCalls = append(toolCalls, event.toolCall)
+		case FunctionGemmaEventContent:
+			contentSb.WriteString(event.content)
+		}
+	}
+
+	return contentSb.String(), "", toolCalls, nil
+}
+
+func (p *FunctionGemmaParser) parseEvents() []functionGemmaEvent {
+	var all []functionGemmaEvent
+
+	keepLooping := true
+	for keepLooping {
+		var events []functionGemmaEvent
+		events, keepLooping = p.eat()
+		if len(events) > 0 {
+			all = append(all, events...)
+		}
+	}
+
+	return all
+}
+
+// emitWithPartialCheck extracts unambiguous content before a potential partial tag
+func (p *FunctionGemmaParser) emitWithPartialCheck(bufStr, tag string) (unambiguous, ambiguous string) {
+	if overlapLen := overlap(bufStr, tag); overlapLen > 0 {
+		beforePartialTag := bufStr[:len(bufStr)-overlapLen]
+		return beforePartialTag, bufStr[len(beforePartialTag):]
+	}
+	return bufStr, ""
+}
+
+func (p *FunctionGemmaParser) eat() ([]functionGemmaEvent, bool) {
+	bufStr := p.buffer.String()
+	if bufStr == "" {
+		return nil, false
+	}
+
+	switch p.state {
+	case FunctionGemmaCollectingContent:
+		if strings.Contains(bufStr, functionGemmaFunctionCallOpen) {
+			split := strings.SplitN(bufStr, functionGemmaFunctionCallOpen, 2)
+			content := split[0]
+			p.buffer.Reset()
+			p.buffer.WriteString(split[1])
+			p.state = FunctionGemmaCollectingToolCalls
+			if content != "" {
+				return []functionGemmaEvent{FunctionGemmaEventContent{content: content}}, true
+			}
+			return nil, true
+		}
+		unambig, ambig := p.emitWithPartialCheck(bufStr, functionGemmaFunctionCallOpen)
+		p.buffer.Reset()
+		p.buffer.WriteString(ambig)
+		if unambig != "" {
+			return []functionGemmaEvent{FunctionGemmaEventContent{content: unambig}}, false
+		}
+		return nil, false
+
+	case FunctionGemmaCollectingToolCalls:
+		if strings.Contains(bufStr, functionGemmaFunctionCallClose) {
+			split := strings.SplitN(bufStr, functionGemmaFunctionCallClose, 2)
+			remaining := split[1]
+			p.buffer.Reset()
+			p.buffer.WriteString(remaining)
+
+			var events []functionGemmaEvent
+			if tc, err := p.parseToolCall(split[0]); err == nil {
+				events = append(events, functionGemmaEventToolCall{toolCall: tc})
+			}
+
+			if !strings.Contains(remaining, functionGemmaFunctionCallOpen) {
+				p.state = FunctionGemmaCollectingContent
+			}
+			return events, true
+		}
+		return nil, false
+	}
+
+	return nil, false
+}
+
+// Matches call:function_name{args}
+var functionGemmaCallRegex = regexp.MustCompile(`call:([^{]+)\{(.*)\}`)
+
+func (p *FunctionGemmaParser) parseToolCall(content string) (api.ToolCall, error) {
+	toolCall := api.ToolCall{}
+
+	// Extract function name and arguments
+	match := functionGemmaCallRegex.FindStringSubmatch(content)
+	if len(match) < 3 {
+		return toolCall, nil
+	}
+
+	toolCall.Function.Name = match[1]
+	argsStr := match[2]
+
+	// Parse arguments
+	toolCall.Function.Arguments = p.parseArguments(argsStr)
+
+	return toolCall, nil
+}
+
+// parseArguments parses the key:value,key:value format
+func (p *FunctionGemmaParser) parseArguments(argsStr string) api.ToolCallFunctionArguments {
+	args := make(api.ToolCallFunctionArguments)
+	if argsStr == "" {
+		return args
+	}
+
+	// Split by comma, but handle nested structures
+	parts := p.splitArguments(argsStr)
+
+	for _, part := range parts {
+		// Find the first colon to split key:value
+		colonIdx := strings.Index(part, ":")
+		if colonIdx == -1 {
+			continue
+		}
+
+		key := part[:colonIdx]
+		value := part[colonIdx+1:]
+
+		// Parse the value
+		args[key] = p.parseValue(value)
+	}
+
+	return args
+}
+
+// splitArguments splits arguments by comma, respecting nested structures
+func (p *FunctionGemmaParser) splitArguments(argsStr string) []string {
+	var parts []string
+	var current strings.Builder
+	depth := 0
+	inEscape := false
+
+	for i := 0; i < len(argsStr); i++ {
+		ch := argsStr[i]
+
+		// Check for <escape> tags
+		if i+8 <= len(argsStr) && argsStr[i:i+8] == "<escape>" {
+			inEscape = !inEscape
+			current.WriteString("<escape>")
+			i += 7 // Skip the rest of <escape>
+			continue
+		}
+
+		if !inEscape {
+			switch ch {
+			case '{', '[':
+				depth++
+				current.WriteByte(ch)
+			case '}', ']':
+				depth--
+				current.WriteByte(ch)
+			case ',':
+				if depth == 0 {
+					if current.Len() > 0 {
+						parts = append(parts, current.String())
+						current.Reset()
+					}
+					continue
+				}
+				current.WriteByte(ch)
+			default:
+				current.WriteByte(ch)
+			}
+		} else {
+			current.WriteByte(ch)
+		}
+	}
+
+	if current.Len() > 0 {
+		parts = append(parts, current.String())
+	}
+
+	return parts
+}
+
+// parseValue parses a single value from the FunctionGemma format
+func (p *FunctionGemmaParser) parseValue(value string) any {
+	// Check for escaped string
+	if strings.HasPrefix(value, "<escape>") && strings.HasSuffix(value, "<escape>") {
+		// Remove the escape tags
+		return value[8 : len(value)-8]
+	}
+
+	// Check for boolean
+	if value == "true" {
+		return true
+	}
+	if value == "false" {
+		return false
+	}
+
+	// Check for number
+	if num, ok := parseNumber(value); ok {
+		return num
+	}
+
+	// Check for array
+	if strings.HasPrefix(value, "[") && strings.HasSuffix(value, "]") {
+		return p.parseArray(value[1 : len(value)-1])
+	}
+
+	// Check for object
+	if strings.HasPrefix(value, "{") && strings.HasSuffix(value, "}") {
+		return p.parseObject(value[1 : len(value)-1])
+	}
+
+	// Default to string
+	return value
+}
+
+// parseArray parses an array value
+func (p *FunctionGemmaParser) parseArray(content string) []any {
+	var result []any
+	parts := p.splitArguments(content)
+	for _, part := range parts {
+		result = append(result, p.parseValue(part))
+	}
+	return result
+}
+
+// parseObject parses an object value
+func (p *FunctionGemmaParser) parseObject(content string) map[string]any {
+	result := make(map[string]any)
+	parts := p.splitArguments(content)
+	for _, part := range parts {
+		colonIdx := strings.Index(part, ":")
+		if colonIdx == -1 {
+			continue
+		}
+		key := part[:colonIdx]
+		value := part[colonIdx+1:]
+		result[key] = p.parseValue(value)
+	}
+	return result
+}
+
+// parseNumber tries to parse a string as a number
+func parseNumber(s string) (any, bool) {
+	// Try integer first
+	var intVal int64
+	if _, err := fmt.Sscanf(s, "%d", &intVal); err == nil {
+		// Check if the entire string was consumed
+		if fmt.Sprintf("%d", intVal) == s {
+			return intVal, true
+		}
+	}
+
+	// Try float
+	var floatVal float64
+	if _, err := fmt.Sscanf(s, "%f", &floatVal); err == nil {
+		return floatVal, true
+	}
+
+	return nil, false
+}

model/parsers/functiongemma_test.go

+package parsers
+
+import (
+	"testing"
+
+	"github.com/ollama/ollama/api"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFunctionGemmaParser(t *testing.T) {
+	tests := []struct {
+		name          string
+		chunks        []string
+		tools         []api.Tool
+		expectedCalls []api.ToolCall
+		expectedText  string
+	}{
+		{
+			name:          "plain_content",
+			chunks:        []string{"H", "e", "l", "l", "o", ",", " ", "w", "o", "r", "l", "d", "!"},
+			expectedCalls: nil,
+			expectedText:  "Hello, world!",
+		},
+		{
+			name: "simple_tool_call",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "get", "_", "weather", "{",
+				"city", ":", "<", "escape", ">", "Paris", "<", "escape", ">",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			tools: []api.Tool{
+				{
+					Type: "function",
+					Function: api.ToolFunction{
+						Name: "get_weather",
+						Parameters: api.ToolFunctionParameters{
+							Type: "object",
+							Properties: map[string]api.ToolProperty{
+								"city": {Type: api.PropertyType{"string"}},
+							},
+						},
+					},
+				},
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "get_weather",
+						Arguments: api.ToolCallFunctionArguments{"city": "Paris"},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "content_before_tool_call",
+			chunks: []string{
+				"L", "et", " ", "me", " ", "check", ".",
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "get", "_", "weather", "{",
+				"city", ":", "<", "escape", ">", "Paris", "<", "escape", ">",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "get_weather",
+						Arguments: api.ToolCallFunctionArguments{"city": "Paris"},
+					},
+				},
+			},
+			expectedText: "Let me check.",
+		},
+		{
+			name: "numeric_arguments",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "add", "{",
+				"a", ":", "1", ",", "b", ":", "2",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "add",
+						Arguments: api.ToolCallFunctionArguments{"a": int64(1), "b": int64(2)},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "boolean_arguments",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "set", "_", "flag", "{",
+				"enabled", ":", "true", ",", "verbose", ":", "false",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "set_flag",
+						Arguments: api.ToolCallFunctionArguments{"enabled": true, "verbose": false},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "multiple_tool_calls",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "get", "_", "weather", "{",
+				"city", ":", "<", "escape", ">", "Paris", "<", "escape", ">",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "get", "_", "weather", "{",
+				"city", ":", "<", "escape", ">", "London", "<", "escape", ">",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "get_weather",
+						Arguments: api.ToolCallFunctionArguments{"city": "Paris"},
+					},
+				},
+				{
+					Function: api.ToolCallFunction{
+						Name:      "get_weather",
+						Arguments: api.ToolCallFunctionArguments{"city": "London"},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "array_argument",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "process", "{",
+				"items", ":", "[",
+				"<", "escape", ">", "a", "<", "escape", ">", ",",
+				"<", "escape", ">", "b", "<", "escape", ">", ",",
+				"<", "escape", ">", "c", "<", "escape", ">",
+				"]",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "process",
+						Arguments: api.ToolCallFunctionArguments{"items": []any{"a", "b", "c"}},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "object_argument",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "update", "{",
+				"data", ":", "{",
+				"name", ":", "<", "escape", ">", "test", "<", "escape", ">", ",",
+				"value", ":", "42",
+				"}",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name: "update",
+						Arguments: api.ToolCallFunctionArguments{
+							"data": map[string]any{"name": "test", "value": int64(42)},
+						},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name:          "empty_input",
+			chunks:        []string{},
+			expectedCalls: nil,
+			expectedText:  "",
+		},
+		{
+			name: "tool_call_with_no_arguments",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "get", "_", "time", "{", "}",
+				"<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "get_time",
+						Arguments: api.ToolCallFunctionArguments{},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "content_with_angle_brackets",
+			chunks: []string{
+				"The", " ", "result", " ", "is", " ", "a", " ", "<", "value", ">", " ", "tag",
+			},
+			expectedCalls: nil,
+			expectedText:  "The result is a <value> tag",
+		},
+		{
+			name: "float_argument",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "set", "_", "temp", "{",
+				"value", ":", "3", ".", "14",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "set_temp",
+						Arguments: api.ToolCallFunctionArguments{"value": 3.14},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "content_after_tool_call",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "test", "{", "}",
+				"<", "end", "_", "function", "_", "call", ">",
+				"Done", "!",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "test",
+						Arguments: api.ToolCallFunctionArguments{},
+					},
+				},
+			},
+			expectedText: "Done!",
+		},
+		{
+			name: "unicode_content_and_arguments",
+			chunks: []string{
+				"こんにちは", " ",
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "greet", "{",
+				"name", ":", "<", "escape", ">", "日本語", "<", "escape", ">",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "greet",
+						Arguments: api.ToolCallFunctionArguments{"name": "日本語"},
+					},
+				},
+			},
+			expectedText: "こんにちは ",
+		},
+		{
+			name: "multiple_params_sorted",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "search", "{",
+				"query", ":", "<", "escape", ">", "test", "<", "escape", ">", ",",
+				"limit", ":", "10", ",",
+				"offset", ":", "0",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name: "search",
+						Arguments: api.ToolCallFunctionArguments{
+							"query":  "test",
+							"limit":  int64(10),
+							"offset": int64(0),
+						},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "nested_object_argument",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "create", "{",
+				"config", ":", "{",
+				"settings", ":", "{",
+				"enabled", ":", "true", ",",
+				"name", ":", "<", "escape", ">", "test", "<", "escape", ">",
+				"}",
+				"}",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name: "create",
+						Arguments: api.ToolCallFunctionArguments{
+							"config": map[string]any{
+								"settings": map[string]any{
+									"enabled": true,
+									"name":    "test",
+								},
+							},
+						},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "partial_start_tag_in_content",
+			chunks: []string{
+				"Hello", " ", "<", "start", " ", "world",
+			},
+			expectedCalls: nil,
+			expectedText:  "Hello <start world",
+		},
+		{
+			name: "parallel_tool_calls",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "get", "_", "weather", "{",
+				"city", ":", "<", "escape", ">", "Paris", "<", "escape", ">",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "get", "_", "time", "{",
+				"timezone", ":", "<", "escape", ">", "UTC", "<", "escape", ">",
+				"}", "<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "get_weather",
+						Arguments: api.ToolCallFunctionArguments{"city": "Paris"},
+					},
+				},
+				{
+					Function: api.ToolCallFunction{
+						Name:      "get_time",
+						Arguments: api.ToolCallFunctionArguments{"timezone": "UTC"},
+					},
+				},
+			},
+			expectedText: "",
+		},
+		{
+			name: "content_between_tool_calls",
+			chunks: []string{
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "first", "{", "}",
+				"<", "end", "_", "function", "_", "call", ">",
+				"Some", " ", "text", " ", "here",
+				"<", "start", "_", "function", "_", "call", ">",
+				"call", ":", "second", "{", "}",
+				"<", "end", "_", "function", "_", "call", ">",
+			},
+			expectedCalls: []api.ToolCall{
+				{
+					Function: api.ToolCallFunction{
+						Name:      "first",
+						Arguments: api.ToolCallFunctionArguments{},
+					},
+				},
+				{
+					Function: api.ToolCallFunction{
+						Name:      "second",
+						Arguments: api.ToolCallFunctionArguments{},
+					},
+				},
+			},
+			expectedText: "Some text here",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			parser := &FunctionGemmaParser{}
+			parser.Init(tt.tools, nil, nil)
+
+			var allContent string
+			var allCalls []api.ToolCall
+
+			for i, chunk := range tt.chunks {
+				done := i == len(tt.chunks)-1
+				content, _, calls, err := parser.Add(chunk, done)
+				assert.NoError(t, err)
+				allContent += content
+				allCalls = append(allCalls, calls...)
+			}
+
+			// Handle empty chunks case
+			if len(tt.chunks) == 0 {
+				content, _, calls, err := parser.Add("", true)
+				assert.NoError(t, err)
+				allContent = content
+				allCalls = calls
+			}
+
+			assert.Equal(t, tt.expectedText, allContent)
+			assert.Equal(t, tt.expectedCalls, allCalls)
+		})
+	}
+}
+
+func TestFunctionGemmaParser_HasSupport(t *testing.T) {
+	parser := &FunctionGemmaParser{}
+	assert.True(t, parser.HasToolSupport())
+	assert.False(t, parser.HasThinkingSupport())
+}

model/parsers/parsers.go

@@ -66,6 +66,8 @@ func ParserForName(name string) Parser {
 		return &Olmo3ThinkParser{}
 	case "nemotron-3-nano":
 		return &Nemotron3NanoParser{}
+	case "functiongemma":
+		return &FunctionGemmaParser{}
 	default:
 		return nil
 	}

model/renderers/functiongemma.go

+package renderers
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/ollama/ollama/api"
+)
+
+type FunctionGemmaRenderer struct{}
+
+const defaultSystemMessage = "You can do function calling with the following functions:"
+
+func (r *FunctionGemmaRenderer) Render(messages []api.Message, tools []api.Tool, thinkValue *api.ThinkValue) (string, error) {
+	var sb strings.Builder
+
+	sb.WriteString("<bos>")
+
+	var systemMessage string
+	var loopMessages []api.Message
+	if len(messages) > 0 && (messages[0].Role == "system" || messages[0].Role == "developer") {
+		systemMessage = messages[0].Content
+		loopMessages = messages[1:]
+	} else {
+		loopMessages = messages
+	}
+
+	if systemMessage != "" || len(tools) > 0 {
+		sb.WriteString("<start_of_turn>developer\n")
+		if systemMessage != "" {
+			sb.WriteString(strings.TrimSpace(systemMessage))
+		}
+		if len(tools) > 0 {
+			if systemMessage != "" {
+				sb.WriteString("\n")
+			}
+			if strings.TrimSpace(systemMessage) != defaultSystemMessage {
+				// Only add default message if user does not provide it
+				sb.WriteString(defaultSystemMessage)
+			}
+		}
+		for _, tool := range tools {
+			sb.WriteString(r.renderToolDeclaration(tool))
+		}
+		sb.WriteString("<end_of_turn>\n")
+	}
+
+	// Track previous message type for tool response handling
+	prevMessageType := ""
+
+	for i, message := range loopMessages {
+		switch message.Role {
+		case "assistant":
+			if prevMessageType != "tool_response" {
+				sb.WriteString("<start_of_turn>model\n")
+			}
+			prevMessageType = ""
+
+			if message.Content != "" {
+				sb.WriteString(strings.TrimSpace(message.Content))
+			}
+
+			if len(message.ToolCalls) > 0 {
+				for _, tc := range message.ToolCalls {
+					sb.WriteString(r.formatToolCall(tc))
+				}
+				// After tool calls, expect tool responses
+				if i+1 < len(loopMessages) && loopMessages[i+1].Role == "tool" {
+					sb.WriteString("<start_function_response>")
+					prevMessageType = "tool_call"
+				} else {
+					sb.WriteString("<end_of_turn>\n")
+				}
+			} else {
+				sb.WriteString("<end_of_turn>\n")
+			}
+
+		case "user":
+			if prevMessageType != "tool_response" {
+				sb.WriteString("<start_of_turn>user\n")
+			}
+			prevMessageType = ""
+			sb.WriteString(strings.TrimSpace(message.Content))
+			sb.WriteString("<end_of_turn>\n")
+
+		case "tool":
+			toolName := ""
+			// Find the tool name from the previous assistant's tool call
+			for j := i - 1; j >= 0; j-- {
+				if loopMessages[j].Role == "assistant" && len(loopMessages[j].ToolCalls) > 0 {
+					// Count how many tool messages came before this one
+					toolIdx := 0
+					for k := j + 1; k < i; k++ {
+						if loopMessages[k].Role == "tool" {
+							toolIdx++
+						}
+					}
+					if toolIdx < len(loopMessages[j].ToolCalls) {
+						toolName = loopMessages[j].ToolCalls[toolIdx].Function.Name
+					}
+					break
+				}
+			}
+
+			if prevMessageType != "tool_call" {
+				sb.WriteString("<start_function_response>")
+			}
+			sb.WriteString("response:" + toolName + "{" + r.formatArgValue(message.Content) + "}<end_function_response>")
+			prevMessageType = "tool_response"
+
+		default:
+			sb.WriteString("<start_of_turn>" + message.Role + "\n")
+			sb.WriteString(strings.TrimSpace(message.Content))
+			sb.WriteString("<end_of_turn>\n")
+		}
+	}
+
+	if prevMessageType != "tool_response" {
+		sb.WriteString("<start_of_turn>model\n")
+	}
+
+	return sb.String(), nil
+}
+
+func (r *FunctionGemmaRenderer) renderToolDeclaration(tool api.Tool) string {
+	var sb strings.Builder
+
+	fn := tool.Function
+	sb.WriteString("<start_function_declaration>declaration:" + fn.Name + "{")
+	sb.WriteString("description:<escape>" + fn.Description + "<escape>")
+
+	if fn.Parameters.Properties != nil || fn.Parameters.Type != "" {
+		sb.WriteString(",parameters:{")
+
+		needsComma := false
+
+		// Only include properties:{} if there are actual properties
+		if len(fn.Parameters.Properties) > 0 {
+			sb.WriteString("properties:{")
+			r.writeProperties(&sb, fn.Parameters.Properties)
+			sb.WriteString("}")
+			needsComma = true
+		}
+
+		if len(fn.Parameters.Required) > 0 {
+			if needsComma {
+				sb.WriteString(",")
+			}
+			sb.WriteString("required:[")
+			for i, req := range fn.Parameters.Required {
+				if i > 0 {
+					sb.WriteString(",")
+				}
+				sb.WriteString("<escape>" + req + "<escape>")
+			}
+			sb.WriteString("]")
+			needsComma = true
+		}
+
+		if fn.Parameters.Type != "" {
+			if needsComma {
+				sb.WriteString(",")
+			}
+			sb.WriteString("type:<escape>" + strings.ToUpper(fn.Parameters.Type) + "<escape>")
+		}
+
+		sb.WriteString("}")
+	}
+
+	sb.WriteString("}<end_function_declaration>")
+	return sb.String()
+}
+
+func (r *FunctionGemmaRenderer) writeProperties(sb *strings.Builder, props map[string]api.ToolProperty) {
+	keys := make([]string, 0, len(props))
+	for k := range props {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
+	first := true
+	for _, name := range keys {
+		prop := props[name]
+		if !first {
+			sb.WriteString(",")
+		}
+		first = false
+
+		sb.WriteString(name + ":{description:<escape>")
+		sb.WriteString(prop.Description)
+		sb.WriteString("<escape>")
+
+		if len(prop.Type) > 0 {
+			sb.WriteString(",type:<escape>" + strings.ToUpper(prop.Type[0]) + "<escape>")
+		}
+
+		sb.WriteString("}")
+	}
+}
+
+func (r *FunctionGemmaRenderer) formatToolCall(tc api.ToolCall) string {
+	var sb strings.Builder
+	sb.WriteString("<start_function_call>call:" + tc.Function.Name + "{")
+
+	keys := make([]string, 0, len(tc.Function.Arguments))
+	for k := range tc.Function.Arguments {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
+	first := true
+	for _, key := range keys {
+		value := tc.Function.Arguments[key]
+		if !first {
+			sb.WriteString(",")
+		}
+		first = false
+		sb.WriteString(key + ":" + r.formatArgValue(value))
+	}
+
+	sb.WriteString("}<end_function_call>")
+	return sb.String()
+}
+
+func (r *FunctionGemmaRenderer) formatArgValue(value any) string {
+	switch v := value.(type) {
+	case string:
+		return "<escape>" + v + "<escape>"
+	case bool:
+		if v {
+			return "true"
+		}
+		return "false"
+	case float64:
+		if v == float64(int64(v)) {
+			return fmt.Sprintf("%d", int64(v))
+		}
+		return fmt.Sprintf("%v", v)
+	case int, int64, int32:
+		return fmt.Sprintf("%d", v)
+	case map[string]any:
+		return r.formatMapValue(v)
+	case []any:
+		return r.formatArrayValue(v)
+	default:
+		return fmt.Sprintf("%v", v)
+	}
+}
+
+func (r *FunctionGemmaRenderer) formatMapValue(m map[string]any) string {
+	var sb strings.Builder
+	sb.WriteString("{")
+
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
+	first := true
+	for _, key := range keys {
+		if !first {
+			sb.WriteString(",")
+		}
+		first = false
+		sb.WriteString(key + ":" + r.formatArgValue(m[key]))
+	}
+
+	sb.WriteString("}")
+	return sb.String()
+}
+
+func (r *FunctionGemmaRenderer) formatArrayValue(arr []any) string {
+	var sb strings.Builder
+	sb.WriteString("[")
+
+	for i, item := range arr {
+		if i > 0 {
+			sb.WriteString(",")
+		}
+		sb.WriteString(r.formatArgValue(item))
+	}
+
+	sb.WriteString("]")
+	return sb.String()
+}

model/renderers/renderer.go

@@ -78,6 +78,8 @@ func rendererForName(name string) Renderer {
 		return renderer
 	case "nemotron-3-nano":
 		return &Nemotron3NanoRenderer{}
+	case "functiongemma":
+		return &FunctionGemmaRenderer{}
 	default:
 		return nil
 	}