diff --git a/agents/calculator/calculator.go b/agents/calculator/calculator.go
new file mode 100644
index 0000000..125564b
--- /dev/null
+++ b/agents/calculator/calculator.go
@@ -0,0 +1,259 @@
+package calculator
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+	"unicode"
+
+	"github.com/volcengine/volcengine-go-sdk/service/arkruntime/model"
+)
+
+const (
+	ToolName         = "calculator"
+	ActivationPrompt = "执行简单、确定性的数学四则运算。当用户询问加减乘除、括号表达式、小数运算或需要准确计算表达式结果时，应直接调用此工具；不用于代数推导、方程求解、统计分析或复杂数学证明。"
+)
+
+type ToolArgs struct {
+	Expression string `json:"expression"`
+	Reason     string `json:"reason"`
+}
+
+func ToolDefinition(description string) *model.Tool {
+	description = strings.TrimSpace(description)
+	if description == "" {
+		description = ActivationPrompt
+	}
+	return &model.Tool{
+		Type: model.ToolTypeFunction,
+		Function: &model.FunctionDefinition{
+			Name:        ToolName,
+			Description: description,
+			Parameters: map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"expression": map[string]any{
+						"type":        "string",
+						"description": "要计算的四则运算表达式，例如 12.5*(3+4)/2。仅支持数字、+、-、*、/ 和括号。",
+					},
+					"reason": map[string]any{
+						"type":        "string",
+						"description": "调用计算器工具的原因。",
+					},
+				},
+				"required": []string{"expression"},
+			},
+		},
+	}
+}
+
+func ExecuteTool(args string) (string, error) {
+	var parsed ToolArgs
+	if err := json.Unmarshal([]byte(strings.TrimSpace(args)), &parsed); err != nil {
+		return "", fmt.Errorf("解析计算器工具参数失败: %w", err)
+	}
+	expression := strings.TrimSpace(parsed.Expression)
+	if expression == "" {
+		return "", errors.New("计算表达式不能为空")
+	}
+	result, err := Evaluate(expression)
+	if err != nil {
+		return "", err
+	}
+	return BuildResultContext(expression, result, parsed.Reason), nil
+}
+
+func BuildResultContext(expression string, result float64, routeReason string) string {
+	var b strings.Builder
+	b.WriteString("计算器工具结果。请优先使用这里的精确计算结果回答用户，不要重新心算。\n")
+	fmt.Fprintf(&b, "表达式: %s\n", strings.TrimSpace(expression))
+	fmt.Fprintf(&b, "结果: %s\n", FormatNumber(result))
+	if strings.TrimSpace(routeReason) != "" {
+		b.WriteString("调用原因: " + strings.TrimSpace(routeReason) + "\n")
+	}
+	return b.String()
+}
+
+func FormatNumber(value float64) string {
+	if math.IsInf(value, 0) || math.IsNaN(value) {
+		return fmt.Sprintf("%v", value)
+	}
+	return strconv.FormatFloat(value, 'f', -1, 64)
+}
+
+func Evaluate(expression string) (float64, error) {
+	parser := expressionParser{input: normalizeExpression(expression)}
+	value, err := parser.parseExpression()
+	if err != nil {
+		return 0, err
+	}
+	parser.skipSpaces()
+	if !parser.atEnd() {
+		return 0, fmt.Errorf("表达式包含不支持的字符: %q", parser.peek())
+	}
+	if math.IsInf(value, 0) || math.IsNaN(value) {
+		return 0, errors.New("计算结果无效")
+	}
+	return value, nil
+}
+
+func normalizeExpression(expression string) string {
+	replacer := strings.NewReplacer(
+		"×", "*",
+		"＊", "*",
+		"÷", "/",
+		"／", "/",
+		"（", "(",
+		"）", ")",
+		"＋", "+",
+		"－", "-",
+		"，", ".",
+	)
+	return replacer.Replace(expression)
+}
+
+type expressionParser struct {
+	input string
+	pos   int
+}
+
+func (p *expressionParser) parseExpression() (float64, error) {
+	value, err := p.parseTerm()
+	if err != nil {
+		return 0, err
+	}
+	for {
+		p.skipSpaces()
+		switch p.peek() {
+		case '+':
+			p.pos++
+			rhs, err := p.parseTerm()
+			if err != nil {
+				return 0, err
+			}
+			value += rhs
+		case '-':
+			p.pos++
+			rhs, err := p.parseTerm()
+			if err != nil {
+				return 0, err
+			}
+			value -= rhs
+		default:
+			return value, nil
+		}
+	}
+}
+
+func (p *expressionParser) parseTerm() (float64, error) {
+	value, err := p.parseFactor()
+	if err != nil {
+		return 0, err
+	}
+	for {
+		p.skipSpaces()
+		switch p.peek() {
+		case '*':
+			p.pos++
+			rhs, err := p.parseFactor()
+			if err != nil {
+				return 0, err
+			}
+			value *= rhs
+		case '/':
+			p.pos++
+			rhs, err := p.parseFactor()
+			if err != nil {
+				return 0, err
+			}
+			if rhs == 0 {
+				return 0, errors.New("除数不能为 0")
+			}
+			value /= rhs
+		default:
+			return value, nil
+		}
+	}
+}
+
+func (p *expressionParser) parseFactor() (float64, error) {
+	p.skipSpaces()
+	switch p.peek() {
+	case '+':
+		p.pos++
+		return p.parseFactor()
+	case '-':
+		p.pos++
+		value, err := p.parseFactor()
+		if err != nil {
+			return 0, err
+		}
+		return -value, nil
+	case '(':
+		p.pos++
+		value, err := p.parseExpression()
+		if err != nil {
+			return 0, err
+		}
+		p.skipSpaces()
+		if p.peek() != ')' {
+			return 0, errors.New("缺少右括号")
+		}
+		p.pos++
+		return value, nil
+	default:
+		return p.parseNumber()
+	}
+}
+
+func (p *expressionParser) parseNumber() (float64, error) {
+	p.skipSpaces()
+	start := p.pos
+	dotSeen := false
+	for !p.atEnd() {
+		r := p.peek()
+		if r == '.' {
+			if dotSeen {
+				break
+			}
+			dotSeen = true
+			p.pos++
+			continue
+		}
+		if !unicode.IsDigit(rune(r)) {
+			break
+		}
+		p.pos++
+	}
+	if start == p.pos {
+		if p.atEnd() {
+			return 0, errors.New("表达式不完整")
+		}
+		return 0, fmt.Errorf("期望数字，遇到 %q", p.peek())
+	}
+	value, err := strconv.ParseFloat(p.input[start:p.pos], 64)
+	if err != nil {
+		return 0, fmt.Errorf("解析数字失败: %w", err)
+	}
+	return value, nil
+}
+
+func (p *expressionParser) skipSpaces() {
+	for !p.atEnd() && unicode.IsSpace(rune(p.peek())) {
+		p.pos++
+	}
+}
+
+func (p *expressionParser) peek() byte {
+	if p.atEnd() {
+		return 0
+	}
+	return p.input[p.pos]
+}
+
+func (p *expressionParser) atEnd() bool {
+	return p.pos >= len(p.input)
+}
diff --git a/agents/calculator/calculator_test.go b/agents/calculator/calculator_test.go
new file mode 100644
index 0000000..f5f5e8b
--- /dev/null
+++ b/agents/calculator/calculator_test.go
@@ -0,0 +1,52 @@
+package calculator
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestEvaluateBasicArithmetic(t *testing.T) {
+	tests := []struct {
+		expression string
+		want       float64
+	}{
+		{expression: "1+2*3", want: 7},
+		{expression: "(1+2)*3", want: 9},
+		{expression: "12.5*(3+4)/2", want: 43.75},
+		{expression: "-2 + 3", want: 1},
+		{expression: "（8＋4）÷3", want: 4},
+	}
+	for _, tt := range tests {
+		got, err := Evaluate(tt.expression)
+		if err != nil {
+			t.Fatalf("Evaluate(%q) error: %v", tt.expression, err)
+		}
+		if got != tt.want {
+			t.Fatalf("Evaluate(%q) = %v, want %v", tt.expression, got, tt.want)
+		}
+	}
+}
+
+func TestEvaluateErrors(t *testing.T) {
+	for _, expression := range []string{"1/0", "1+", "(1+2", "2^3"} {
+		if _, err := Evaluate(expression); err == nil {
+			t.Fatalf("Evaluate(%q) expected error", expression)
+		}
+	}
+}
+
+func TestToolDefinitionAndExecuteTool(t *testing.T) {
+	definition := ToolDefinition("custom calculator")
+	if definition.Function == nil || definition.Function.Name != ToolName || definition.Function.Description != "custom calculator" {
+		t.Fatalf("unexpected definition: %#v", definition)
+	}
+	text, err := ExecuteTool(`{"expression":"12.5*(3+4)/2","reason":"用户询问计算结果"}`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range []string{"计算器工具结果", "12.5*(3+4)/2", "43.75", "用户询问计算结果"} {
+		if !strings.Contains(text, want) {
+			t.Fatalf("tool result missing %q:\n%s", want, text)
+		}
+	}
+}
diff --git a/config/config.go b/config/config.go
index 9356a35..66bb234 100644
--- a/config/config.go
+++ b/config/config.go
@@ -17,6 +17,7 @@ const (
 	defaultToolRouterTimeout    = 30
 	defaultToolRouterMaxTokens  = 512
 	defaultToolRouterSystemText = `你可以按需直接调用可用工具来回答用户问题。
+用户询问简单数学计算、四则运算、加减乘除、括号表达式或明确要求算出数值结果时，调用 calculator。
 如果用户问题包含今天、今日、明天、昨天、本周、本月、本年、最近等相对时间，且后续需要搜索或查询数据库，应先调用 time 获取绝对日期范围。
 需要实时网页资料、新闻、当前版本、近期事件、网页核验或用户明确要求联网时，调用 search。
 需要查询本地业务数据、日程、会议、待办、记录、统计或时间范围内数据时，调用 sql。
@@ -105,6 +106,7 @@ func DefaultToolRouterConfig() ToolRouterConfig {
 		MaxTokens:    defaultToolRouterMaxTokens,
 		SystemPrompt: defaultToolRouterSystemText,
 		Tools: []ToolRouteConfig{
+			{Name: "calculator", Enabled: true, Description: ""},
 			{Name: "time", Enabled: true, Description: ""},
 			{Name: "search", Enabled: true, Description: ""},
 			{Name: "sql", Enabled: true, Description: ""},
diff --git a/main_test.go b/main_test.go
index 9cb7879..1a69333 100644
--- a/main_test.go
+++ b/main_test.go
@@ -46,7 +46,7 @@ func TestNormalizeToolRouterConfigDefaults(t *testing.T) {
 	if strings.TrimSpace(cfg.ToolRouter.SystemPrompt) == "" {
 		t.Fatal("system prompt should be defaulted")
 	}
-	if len(cfg.ToolRouter.Tools) != 3 || cfg.ToolRouter.Tools[0].Name != "time" || cfg.ToolRouter.Tools[1].Name != "search" || cfg.ToolRouter.Tools[2].Name != "sql" || !cfg.ToolRouter.Tools[0].Enabled || !cfg.ToolRouter.Tools[1].Enabled || !cfg.ToolRouter.Tools[2].Enabled {
+	if len(cfg.ToolRouter.Tools) != 4 || cfg.ToolRouter.Tools[0].Name != "calculator" || cfg.ToolRouter.Tools[1].Name != "time" || cfg.ToolRouter.Tools[2].Name != "search" || cfg.ToolRouter.Tools[3].Name != "sql" || !cfg.ToolRouter.Tools[0].Enabled || !cfg.ToolRouter.Tools[1].Enabled || !cfg.ToolRouter.Tools[2].Enabled || !cfg.ToolRouter.Tools[3].Enabled {
 		t.Fatalf("unexpected tools: %#v", cfg.ToolRouter.Tools)
 	}
 }
@@ -66,7 +66,7 @@ func TestNormalizeOpenAIConfigDefaultsContextWindow(t *testing.T) {
 	}
 }
 
-func TestNormalizeToolRouterConfigAddsTimeBeforeSQL(t *testing.T) {
+func TestNormalizeToolRouterConfigAddsCalculatorAndTimeBeforeSQL(t *testing.T) {
 	cfg := &config.Config{ToolRouter: config.ToolRouterConfig{
 		Enabled:      true,
 		Timeout:      1,
@@ -82,9 +82,9 @@ func TestNormalizeToolRouterConfigAddsTimeBeforeSQL(t *testing.T) {
 		t.Fatal(err)
 	}
 	if !changed {
-		t.Fatal("expected time tool to be added")
+		t.Fatal("expected calculator and time tools to be added")
 	}
-	if len(cfg.ToolRouter.Tools) < 3 || cfg.ToolRouter.Tools[0].Name != "time" || cfg.ToolRouter.Tools[2].Name != "sql" {
+	if len(cfg.ToolRouter.Tools) < 4 || cfg.ToolRouter.Tools[0].Name != "calculator" || cfg.ToolRouter.Tools[1].Name != "time" || cfg.ToolRouter.Tools[3].Name != "sql" {
 		t.Fatalf("unexpected tool order: %#v", cfg.ToolRouter.Tools)
 	}
 }
@@ -112,6 +112,7 @@ func TestAvailableAgentToolsUsesConfigOrderAndEnabled(t *testing.T) {
 		Enabled: true,
 		Tools: []config.ToolRouteConfig{
 			{Name: "search", Enabled: true},
+			{Name: "calculator", Enabled: true, Description: "custom calculator"},
 			{Name: "time", Enabled: true, Description: "custom time"},
 			{Name: "sql", Enabled: false},
 		},
@@ -121,14 +122,14 @@ func TestAvailableAgentToolsUsesConfigOrderAndEnabled(t *testing.T) {
 	}
 
 	tools := toolrouter.AvailableAgentTools(router, ai.ActiveProfile(), nil, nil, nil)
-	if len(tools) != 1 {
+	if len(tools) != 2 {
 		t.Fatalf("tools length = %d", len(tools))
 	}
-	if tools[0].Name() != "time" {
-		t.Fatalf("tool name = %s", tools[0].Name())
+	if tools[0].Name() != "calculator" || tools[1].Name() != "time" {
+		t.Fatalf("unexpected tools: %#v", tools)
 	}
 	definition := tools[0].Definition()
-	if definition.Function == nil || definition.Function.Description != "custom time" {
+	if definition.Function == nil || definition.Function.Description != "custom calculator" {
 		t.Fatalf("unexpected definition: %#v", definition)
 	}
 }
diff --git a/toolrouter/tools.go b/toolrouter/tools.go
index 2784dff..0c16733 100644
--- a/toolrouter/tools.go
+++ b/toolrouter/tools.go
@@ -6,6 +6,7 @@ import (
 	"strings"
 	"time"
 
+	"aichat/agents/calculator"
 	searchagent "aichat/agents/search"
 	sqlquery "aichat/agents/sql"
 	timeagent "aichat/agents/time"
@@ -47,6 +48,18 @@ func availableAgentTools(state *State, profile *llm.Profile, searchState *search
 		}
 		description := strings.TrimSpace(item.Description)
 		switch item.Name {
+		case calculator.ToolName:
+			tools = append(tools, AgentTool{
+				name:       calculator.ToolName,
+				definition: calculator.ToolDefinition(description),
+				execute: func(ctx context.Context, args string) (string, error) {
+					result, err := calculator.ExecuteTool(args)
+					if err == nil && emit != nil {
+						emit(stream.Frame{Type: "trace", Tool: calculator.ToolName, Stage: "calculate", Status: "success", Message: "四则运算完成"})
+					}
+					return result, err
+				},
+			})
 		case timeagent.ToolName:
 			tools = append(tools, AgentTool{
 				name:       timeagent.ToolName,