diff --git a/build/build.go b/build/build.go
index 9de1257f..14b5cdb9 100644
--- a/build/build.go
+++ b/build/build.go
@@ -1,6 +1,7 @@
 package build
 
 import (
+	"encoding/json"
 	"fmt"
 	"go/ast"
 	"go/build"
@@ -498,8 +499,10 @@ type Options struct {
 	MapToLocalDisk bool
 	Minify         bool
 	Color          bool
-	BuildTags      []string
 	Rebuild        bool
+	Analyze        bool
+	AnalyzeJson    bool
+	BuildTags      []string
 }
 
 func (o *Options) PrintError(format string, a ...interface{}) {
@@ -965,7 +968,7 @@ func (s *Session) WriteCommandPackage(archive *compiler.Archive, pkgObj string)
 		defer func() {
 			m.WriteTo(mapFile)
 			mapFile.Close()
-			fmt.Fprintf(codeFile, "//# sourceMappingURL=%s.map\n", filepath.Base(pkgObj))
+			fmt.Fprintf(sourceMapFilter.Writer, "//# sourceMappingURL=%s.map\n", filepath.Base(pkgObj))
 		}()
 
 		sourceMapFilter.MappingCallback = NewMappingCallback(m, s.options.GOROOT, s.options.GOPATH, s.options.MapToLocalDisk)
@@ -981,7 +984,27 @@ func (s *Session) WriteCommandPackage(archive *compiler.Archive, pkgObj string)
 	if err != nil {
 		return err
 	}
-	return compiler.WriteProgramCode(deps, sourceMapFilter)
+	infos, err := compiler.WriteProgramCode(deps, sourceMapFilter)
+	if s.options.Analyze {
+		if s.options.AnalyzeJson {
+			data, _ := json.MarshalIndent(&infos, "", "\t")
+			fmt.Println(string(data))
+		} else {
+			var maxSize int64
+			for _, info := range infos {
+				if info.Size > maxSize {
+					maxSize = info.Size
+				}
+			}
+			noff := len(strconv.FormatInt(maxSize, 10))
+			format := fmt.Sprintf("%%%vv\t%%v\n", noff)
+			fmt.Printf(format, "<Size>", "<ImportPath>")
+			for _, info := range infos {
+				fmt.Printf(format, info.Size, info.ImportPath)
+			}
+		}
+	}
+	return err
 }
 
 func NewMappingCallback(m *sourcemap.Map, goroot, gopath string, localMap bool) func(generatedLine, generatedColumn int, originalPos token.Position) {
diff --git a/compiler/compiler.go b/compiler/compiler.go
index 890d26f2..1e94c2ef 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -102,7 +102,7 @@ type dceInfo struct {
 	methodFilter string
 }
 
-func WriteProgramCode(pkgs []*Archive, w *SourceMapFilter) error {
+func WriteProgramCode(pkgs []*Archive, w *SourceMapFilter) ([]*PkgInfo, error) {
 	mainPkg := pkgs[len(pkgs)-1]
 	minify := mainPkg.Minified
 
@@ -152,31 +152,52 @@ func WriteProgramCode(pkgs []*Archive, w *SourceMapFilter) error {
 	}
 
 	if _, err := w.Write([]byte("\"use strict\";\n(function() {\n\n")); err != nil {
-		return err
+		return nil, err
 	}
 	preludeJS := prelude.Prelude
 	if minify {
 		preludeJS = prelude.Minified
 	}
 	if _, err := io.WriteString(w, preludeJS); err != nil {
-		return err
+		return nil, err
 	}
 	if _, err := w.Write([]byte("\n")); err != nil {
-		return err
+		return nil, err
 	}
 
 	// write packages
+	offset := w.offset
+
+	var infos []*PkgInfo
+	infos = append(infos, &PkgInfo{
+		Name:       "$prelude",
+		ImportPath: "$prelude",
+		Size:       w.offset,
+	})
 	for _, pkg := range pkgs {
 		if err := WritePkgCode(pkg, dceSelection, minify, w); err != nil {
-			return err
+			return nil, err
 		}
+		infos = append(infos, &PkgInfo{
+			Name:       pkg.Name,
+			ImportPath: pkg.ImportPath,
+			Imports:    pkg.Imports,
+			Size:       w.offset - offset,
+		})
+		offset = w.offset
 	}
 
 	if _, err := w.Write([]byte("$synthesizeMethods();\nvar $mainPkg = $packages[\"" + string(mainPkg.ImportPath) + "\"];\n$packages[\"runtime\"].$init();\n$go($mainPkg.$init, []);\n$flushConsole();\n\n}).call(this);\n")); err != nil {
-		return err
+		return nil, err
 	}
+	return infos, nil
+}
 
-	return nil
+type PkgInfo struct {
+	Name       string   `json:"Name"`
+	ImportPath string   `json:"ImportPath,omitempty"`
+	Imports    []string `json:"Imports,omitempty"`
+	Size       int64    `json:"Size"`
 }
 
 func WritePkgCode(pkg *Archive, dceSelection map[*Decl]struct{}, minify bool, w *SourceMapFilter) error {
@@ -260,9 +281,14 @@ type SourceMapFilter struct {
 	MappingCallback func(generatedLine, generatedColumn int, originalPos token.Position)
 	line            int
 	column          int
+	offset          int64
 	fileSet         *token.FileSet
 }
 
+func (f *SourceMapFilter) Offset() int64 {
+	return f.offset
+}
+
 func (f *SourceMapFilter) Write(p []byte) (n int, err error) {
 	var n2 int
 	for {
@@ -274,6 +300,7 @@ func (f *SourceMapFilter) Write(p []byte) (n int, err error) {
 
 		n2, err = f.Writer.Write(w)
 		n += n2
+		f.offset += int64(n2)
 		for {
 			i := bytes.IndexByte(w, '\n')
 			if i == -1 {
diff --git a/tool.go b/tool.go
index 1bc6ef57..3fb17edf 100644
--- a/tool.go
+++ b/tool.go
@@ -82,6 +82,8 @@ func main() {
 	compilerFlags.StringVar(&tags, "tags", "", "a list of build tags to consider satisfied during the build")
 	compilerFlags.BoolVar(&options.MapToLocalDisk, "localmap", false, "use local paths for sourcemap")
 	compilerFlags.BoolVarP(&options.Rebuild, "force", "a", false, "force rebuilding of packages that are already up-to-date")
+	compilerFlags.BoolVar(&options.Analyze, "analyze", false, "print analyze build package's info")
+	compilerFlags.BoolVar(&options.AnalyzeJson, "json", false, "print analyze build package's json info")
 
 	flagWatch := pflag.NewFlagSet("", 0)
 	flagWatch.BoolVarP(&options.Watch, "watch", "w", false, "watch for changes to the source files")
@@ -590,7 +592,7 @@ func (fs serveCommandFileSystem) Open(requestName string) (http.File, error) {
 				if err != nil {
 					return err
 				}
-				if err := compiler.WriteProgramCode(deps, sourceMapFilter); err != nil {
+				if _, err = compiler.WriteProgramCode(deps, sourceMapFilter); err != nil {
 					return err
 				}