diff --git a/README.md b/README.md
index 6faa0e2..71d3595 100644
--- a/README.md
+++ b/README.md
@@ -111,6 +111,8 @@ Usage of go-callvis:
     	Enable verbose log.
   -file string
     	output filename - omit to use server mode
+  -cacheDir string
+    	Enable caching to avoid unnecessary re-rendering.
   -focus string
     	Focus specific package using name or import path. (default "main")
   -format string
diff --git a/analysis.go b/analysis.go
index 982e422..b2c5f4d 100644
--- a/analysis.go
+++ b/analysis.go
@@ -78,16 +78,18 @@ func mainPackages(pkgs []*ssa.Package) ([]*ssa.Package, error) {
 }
 
 type renderOpts struct {
-	focus   string
-	group   []string
-	ignore  []string
-	include []string
-	limit   []string
-	nointer bool
-	nostd   bool
+	cacheDir string
+	focus    string
+	group    []string
+	ignore   []string
+	include  []string
+	limit    []string
+	nointer  bool
+	refresh  bool
+	nostd    bool
 }
 
-func (a *analysis) render(opts renderOpts) ([]byte, error) {
+func (a *analysis) render(opts *renderOpts) ([]byte, error) {
 	var (
 		err      error
 		ssaPkg   *ssa.Package
diff --git a/handler.go b/handler.go
index e97bfbf..51432e3 100644
--- a/handler.go
+++ b/handler.go
@@ -3,20 +3,24 @@ package main
 import (
 	"errors"
 	"fmt"
+	"io"
 	"log"
 	"net/http"
+	"os"
+	"path/filepath"
 	"strings"
 )
 
 func analysisSetup() (r renderOpts) {
 	r = renderOpts{
-		focus:   *focusFlag,
-		group:   []string{*groupFlag},
-		ignore:  []string{*ignoreFlag},
-		include: []string{*includeFlag},
-		limit:   []string{*limitFlag},
-		nointer: *nointerFlag,
-		nostd:   *nostdFlag}
+		cacheDir: *cacheDir,
+		focus:    *focusFlag,
+		group:    []string{*groupFlag},
+		ignore:   []string{*ignoreFlag},
+		include:  []string{*includeFlag},
+		limit:    []string{*limitFlag},
+		nointer:  *nointerFlag,
+		nostd:    *nostdFlag}
 
 	return r
 }
@@ -76,6 +80,52 @@ func handler(w http.ResponseWriter, r *http.Request) {
 	logf(" => handling request:  %v", r.URL)
 	logf("----------------------")
 
+	opts := buildOptionsFromRequest(r)
+
+	var img string
+	if img = findCachedImg(opts); img != "" {
+		log.Println("serving file:", img)
+		http.ServeFile(w, r, img)
+		return
+	}
+
+	// Convert list-style args to []string
+	if e := processListArgs(opts); e != nil {
+		http.Error(w, "invalid parameters", http.StatusBadRequest)
+		return
+	}
+
+	output, err := Analysis.render(opts)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	if r.Form.Get("format") == "dot" {
+		log.Println("writing dot output..")
+		fmt.Fprint(w, string(output))
+		return
+	}
+
+	log.Printf("converting dot to %s..\n", *outputFormat)
+
+	img, err = dotToImage("", *outputFormat, output)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	err = cacheImg(opts, img)
+	if err != nil {
+		http.Error(w, "cache img error: "+err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	log.Println("serving file:", img)
+	http.ServeFile(w, r, img)
+}
+
+func buildOptionsFromRequest(r *http.Request) *renderOpts {
 	// get cmdline default for analysis
 	opts := analysisSetup()
 
@@ -91,6 +141,9 @@ func handler(w http.ResponseWriter, r *http.Request) {
 	if inter := r.FormValue("nointer"); inter != "" {
 		opts.nointer = true
 	}
+	if refresh := r.FormValue("refresh"); refresh != "" {
+		opts.refresh = true
+	}
 	if g := r.FormValue("group"); g != "" {
 		opts.group[0] = g
 	}
@@ -104,32 +157,89 @@ func handler(w http.ResponseWriter, r *http.Request) {
 		opts.include[0] = inc
 	}
 
-	// Convert list-style args to []string
-	if e := processListArgs(&opts); e != nil {
-		http.Error(w, "invalid parameters", http.StatusBadRequest)
-		return
+	return &opts
+}
+
+func findCachedImg(opts *renderOpts) string {
+	if opts.cacheDir == "" || opts.refresh {
+		return ""
 	}
 
-	output, err := Analysis.render(opts)
+	focus := opts.focus
+	if focus == "" {
+		focus = "all"
+	}
+	focusFilePath := focus + "." + *outputFormat
+	absFilePath := filepath.Join(opts.cacheDir, focusFilePath)
+
+	if exists, err := pathExists(absFilePath); err != nil || !exists {
+		log.Println("not cached img:", absFilePath)
+		return ""
+	}
+
+	log.Println("hit cached img")
+	return absFilePath
+}
+
+func cacheImg(opts *renderOpts, img string) error {
+	if opts.cacheDir == "" || img == "" {
+		return nil
+	}
+
+	focus := opts.focus
+	if focus == "" {
+		focus = "all"
+	}
+	absCacheDirPrefix := filepath.Join(opts.cacheDir, focus)
+	absCacheDirPath := strings.TrimRightFunc(absCacheDirPrefix, func(r rune) bool {
+		return r != '\\' && r != '/'
+	})
+	err := os.MkdirAll(absCacheDirPath, os.ModePerm)
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
-		return
+		return err
 	}
 
-	if r.Form.Get("format") == "dot" {
-		log.Println("writing dot output..")
-		fmt.Fprint(w, string(output))
-		return
+	absFilePath := absCacheDirPrefix + "." + *outputFormat
+	_, err = copyFile(img, absFilePath)
+	if err != nil {
+		return err
 	}
 
-	log.Printf("converting dot to %s..\n", *outputFormat)
+	return nil
+}
+
+func pathExists(path string) (bool, error) {
+	_, err := os.Stat(path)
+	if err == nil {
+		return true, nil
+	}
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	return false, err
+}
 
-	img, err := dotToImage("", *outputFormat, output)
+func copyFile(src, dst string) (int64, error) {
+	sourceFileStat, err := os.Stat(src)
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
-		return
+		return 0, err
 	}
 
-	log.Println("serving file:", img)
-	http.ServeFile(w, r, img)
+	if !sourceFileStat.Mode().IsRegular() {
+		return 0, fmt.Errorf("%s is not a regular file", src)
+	}
+
+	source, err := os.Open(src)
+	if err != nil {
+		return 0, err
+	}
+	defer source.Close()
+
+	destination, err := os.Create(dst)
+	if err != nil {
+		return 0, err
+	}
+	defer destination.Close()
+	nBytes, err := io.Copy(destination, source)
+	return nBytes, err
 }
diff --git a/main.go b/main.go
index 80aafa9..3c42f76 100644
--- a/main.go
+++ b/main.go
@@ -32,6 +32,7 @@ var (
 	skipBrowser  = flag.Bool("skipbrowser", false, "Skip opening browser.")
 	outputFile   = flag.String("file", "", "output filename - omit to use server mode")
 	outputFormat = flag.String("format", "svg", "output file format [svg | png | jpg | ...]")
+	cacheDir     = flag.String("cacheDir", "", "Enable caching to avoid unnecessary re-rendering, you can force rendering by adding 'refresh=true' to the URL query or emptying the cache directory")
 
 	debugFlag   = flag.Bool("debug", false, "Enable verbose log.")
 	versionFlag = flag.Bool("version", false, "Show version and exit.")
@@ -63,7 +64,7 @@ func outputDot(fname string, outputFormat string) {
 		log.Fatalf("%v\n", e)
 	}
 
-	output, err := Analysis.render(opts)
+	output, err := Analysis.render(&opts)
 	if err != nil {
 		log.Fatalf("%v\n", err)
 	}