diff --git a/tools/tinygoize/build.go b/tools/tinygoize/build.go
index a970331811..37da037cd8 100644
--- a/tools/tinygoize/build.go
+++ b/tools/tinygoize/build.go
@@ -20,8 +20,14 @@ const (
 	BuildCodeFatal
 )
 
-// Additional tags required for specific commands. Assume command names unique
-// despite being in different directories.
+type BuildRes struct {
+	err *exec.ExitError
+	excluded bool
+	output []byte
+}
+
+// Additional tags required for specific commands. Assumes command names are
+// unique despite being in different directories.
 var addBuildTags = map[string]string{
 	"gzip":     "noasm",
 	"insmod":   "noasm",
@@ -33,7 +39,7 @@ var addBuildTags = map[string]string{
 	"init":     "noasm",
 }
 
-// returns the needed build-tags for a given package
+// Returns the needed build-tags for a given package
 func buildTags(dir string) (tags string) {
 	parts := strings.Split(dir, "/")
 	cmd := parts[len(parts)-1]
@@ -65,35 +71,38 @@ func isExcluded(dir string) bool {
 }
 
 // "tinygo build" in directory 'dir'
-func build(id int, tinygo *string, dir string) (BuildCode, error) {
-
+func build(id int, tinygo *string, dir string) (res BuildRes, err error) {
 	wlog := func(format string, args ...interface{}) {
 		log.Printf("[%d] "+format, append([]interface{}{id}, args...)...)
 	}
-
 	wlog("%s Building...\n", dir)
-
 	tags := []string{"tinygo.enable"}
 	if addTags := buildTags(dir); addTags != "" {
 		tags = append(tags, addTags)
 	}
-	c := exec.Command(*tinygo, "build", "-tags", strings.Join(tags, ","))
-	c.Dir = dir
-	c.Stdout, c.Stderr = os.Stdout, os.Stderr
-	c.Env = append(os.Environ(), "GOOS=linux", "GOARCH=amd64")
-	err := c.Run()
+	cmd := exec.Command(*tinygo, "build", "-tags", strings.Join(tags, ","))
+	cmd.Env = append(os.Environ(), "GOOS=linux", "GOARCH=amd64")
+	cmd.Dir = dir
+	res.output, err = cmd.CombinedOutput()
 	if err != nil {
-		berr, ok := err.(*exec.ExitError)
+		var ok bool
+		res.err, ok = err.(*exec.ExitError)
 		if !ok {
-			return BuildCodeFatal, err
+			return
 		}
+		err = nil
 		if isExcluded(dir) {
 			wlog("%v EXCLUDED\n", dir)
-			return BuildCodeExclude, nil
+			res.excluded = true
+			return
+		}
+		lines := strings.Split(string(res.output), "\n")
+		for _,line := range lines {
+			wlog(line)
 		}
-		wlog("%v FAILED %v\n", dir, berr)
-		return BuildCodeFailed, nil
+		wlog("%v FAILED %v\n", dir, res.err)
+		return
 	}
 	wlog("%v PASS\n", dir)
-	return BuildCodeSuccess, nil
+	return
 }
diff --git a/tools/tinygoize/config.go b/tools/tinygoize/config.go
new file mode 100644
index 0000000000..b41f7ecfc7
--- /dev/null
+++ b/tools/tinygoize/config.go
@@ -0,0 +1,14 @@
+// Copyright 2017-2024 the u-root Authors. All rights reserved
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+type Config struct {
+	pathMD string
+	tinygo string
+	nWorkers int
+	checkOnly bool
+	verbose bool
+	dirs []string
+}
diff --git a/tools/tinygoize/constraints.go b/tools/tinygoize/constraints.go
index e95e683d4c..ed47f25f22 100644
--- a/tools/tinygoize/constraints.go
+++ b/tools/tinygoize/constraints.go
@@ -23,96 +23,118 @@ const (
 )
 
 // Modifies, adds, or removes //go:build line as appropriate with '!tinygo ||
-// tinygo.enable' for all .go files in dir depending on whether it 'builds' or
-// not as previously tested.
-func fixupConstraints(dir string, builds bool) (err error) {
-	p := printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
-
-	files, err := filepath.Glob(filepath.Join(dir, "*"))
+// tinygo.enable'
+func fixupFileConstraints(file string, builds bool, checkonly bool) (mustDoWork bool, err error) {
+	log.Printf("Process %s", file)
+	b, err := os.ReadFile(file)
 	if err != nil {
 		log.Fatal(err)
 	}
-nextFile:
-	for _, file := range files {
-		if !strings.HasSuffix(file, ".go") {
-			continue
-		}
-		log.Printf("Process %s", file)
-		b, err := os.ReadFile(file)
-		if err != nil {
-			log.Fatal(err)
-		}
-		fset := token.NewFileSet() // positions are relative to fset
-		f, err := parser.ParseFile(fset, file, string(b), parser.ParseComments|parser.SkipObjectResolution)
-		if err != nil {
-			log.Fatalf("parsing\n%v\n:%v", string(b), err)
-		}
+	fset := token.NewFileSet() // positions are relative to fset
+	f, err := parser.ParseFile(fset, file, string(b), parser.ParseComments|parser.SkipObjectResolution)
+	if err != nil {
+		log.Fatalf("parsing\n%v\n:%v", string(b), err)
+	}
 
-		goBuildPresent := false
+	goBuildPresent := false
 
-	done:
-		// modify existing //go:build line
-		for _, cg := range f.Comments {
-			for _, c := range cg.List {
-				if !strings.HasPrefix(c.Text, goBuild) {
-					continue
-				}
-				goBuildPresent = true
+	// modify existing //go:build line
+	for _, cg := range f.Comments {
+		for _, c := range cg.List {
+			if !strings.HasPrefix(c.Text, goBuild) {
+				continue
+			}
+			goBuildPresent = true
 
-				contains := strings.Contains(c.Text, constraint)
+			contains := strings.Contains(c.Text, constraint)
 
-				if (builds && !contains) || (!builds && contains) {
-					log.Printf("Skipped, constraint up-to-date: %s\n", file)
-					continue nextFile
-				}
+			if (builds && !contains) || (!builds && contains) {
+				log.Printf("Skipped, constraint up-to-date: %s\n", file)
+				return
+			}
+
+			if builds {
+				re := regexp.MustCompile(`\(?\s*!tinygo\s+\|\|\s+tinygo.enable\s*\)?(\s+\&\&)?`)
+				c.Text = re.ReplaceAllString(c.Text, "")
+				log.Printf("Stripping build constraint %v\n", file)
 
-				if builds {
-					re := regexp.MustCompile(`\(?\s*!tinygo\s+\|\|\s+tinygo.enable\s*\)?(\s+\&\&)?`)
-					c.Text = re.ReplaceAllString(c.Text, "")
-					log.Printf("Stripping build constraint %v\n", file)
-
-					// handle potentially now-empty build constraint
-					re = regexp.MustCompile(`^\s*//go:build\s*$`)
-					if re.MatchString(c.Text) {
-						filtered := []*ast.Comment{}
-						for _, comment := range cg.List {
-							if !re.MatchString(comment.Text) {
-								filtered = append(filtered, comment)
-							}
+				// handle potentially now-empty build constraint
+				re = regexp.MustCompile(`^\s*//go:build\s*$`)
+				if re.MatchString(c.Text) {
+					filtered := []*ast.Comment{}
+					for _, comment := range cg.List {
+						if !re.MatchString(comment.Text) {
+							filtered = append(filtered, comment)
 						}
-						cg.List = filtered
 					}
-				} else {
-					c.Text = goBuild + "(" + constraint + ") && (" + c.Text[len(goBuild):] + ")"
+					cg.List = filtered
 				}
-				break done
+			} else {
+				c.Text = goBuild + "(" + constraint + ") && (" + c.Text[len(goBuild):] + ")"
 			}
+			break
 		}
+	}
 
-		if !builds && !goBuildPresent {
-			// no //go:build line found: insert one
-			var cg ast.CommentGroup
-			cg.List = append(cg.List, &ast.Comment{Text: goBuild + constraint})
-
-			if len(f.Comments) > 0 {
-				// insert //go:build after first comment
-				// group, assumed copyright. Doesn't seem
-				// quite right but seems to work.
-				cg.List[0].Slash = f.Comments[0].List[0].Slash + 1
-				f.Comments = append([]*ast.CommentGroup{f.Comments[0], &cg}, f.Comments[1:]...)
-			} else {
-				// prepend //go:build
-				f.Comments = append([]*ast.CommentGroup{&cg}, f.Comments...)
-			}
+	// if it doesn't build but no //go:build found, insert one XXX skip space after copyright
+	if !builds && !goBuildPresent {
+		// no //go:build line found: insert one
+		var cg ast.CommentGroup
+		cg.List = append(cg.List, &ast.Comment{Text: goBuild + constraint})
+
+		if len(f.Comments) > 0 {
+			// insert //go:build after first comment
+			// group, assumed copyright. Doesn't seem
+			// quite right but seems to work.
+			cg.List[0].Slash = f.Comments[0].List[0].Slash + 1
+			f.Comments = append([]*ast.CommentGroup{f.Comments[0], &cg}, f.Comments[1:]...)
+		} else {
+			// prepend //go:build
+			f.Comments = append([]*ast.CommentGroup{&cg}, f.Comments...)
 		}
+	}
+
+	// Complete source file.
+	var buf bytes.Buffer
+	p := printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
+	if err = p.Fprint(&buf, fset, f); err != nil {
+		log.Fatalf("Printing:%v", err)
+	}
+
 
-		// Complete source file.
-		var buf bytes.Buffer
-		if err = p.Fprint(&buf, fset, f); err != nil {
-			log.Fatalf("Printing:%v", err)
+	if bytes.Equal(b, buf.Bytes()) {
+		log.Printf("Skipped, constraint up-to-date: %s\n", file)
+		return
+	} else {
+		mustDoWork = true
+	}
+	if checkonly {
+		return
+	}
+
+	if err := os.WriteFile(file, buf.Bytes(), 0o644); err != nil {
+		log.Fatal(err)
+	}
+	return
+}
+
+// fixup build constraint lines for all .go files in pkg
+func fixupPkgConstraints(dir string, builds bool, checkonly bool) (mustDoWork bool, err error) {
+	files, err := filepath.Glob(filepath.Join(dir, "*"))
+	if err != nil {
+		log.Fatal(err)
+	}
+	for _, file := range files {
+		if !strings.HasSuffix(file, ".go") {
+			continue
+		}
+		mdw, err2 := fixupFileConstraints(file, builds, checkonly)
+		if err2 != nil {
+			err = err2
+			return
 		}
-		if err := os.WriteFile(file, buf.Bytes(), 0o644); err != nil {
-			log.Fatal(err)
+		if mdw {
+			mustDoWork = true
 		}
 	}
 	return
diff --git a/tools/tinygoize/main.go b/tools/tinygoize/main.go
index f8f942407e..24961ed769 100644
--- a/tools/tinygoize/main.go
+++ b/tools/tinygoize/main.go
@@ -14,20 +14,14 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"io"
 	"os/exec"
-	"path/filepath"
-	"sort"
 	"strings"
 	"sync"
 	"runtime"
+	"golang.org/x/term"
 )
 
-// Track set of passing, failing, and excluded commands
-type BuildStatus struct {
-	passing  []string
-	failing  []string
-	excluded []string
-}
 
 // return trimmed output of "tinygo version"
 func tinygoVersion(tinygo *string) (string, error) {
@@ -38,44 +32,76 @@ func tinygoVersion(tinygo *string) (string, error) {
 	return strings.TrimSpace(string(out)), err
 }
 
-type BuildResult struct {
-	dir      string
-	code     BuildCode
-	err      error
+func progress(nComplete int, outOf int) {
+	isTerminal := term.IsTerminal(int(os.Stdin.Fd()))
+	if isTerminal {
+		fmt.Printf("\033[2K\r")
+	}
+	percent := 100 * ( float64(nComplete) / float64(outOf))
+	fmt.Printf("%v/%v %.2f%%", nComplete, outOf, percent)
+	if !isTerminal || nComplete == outOf {
+		fmt.Println()
+	}
 }
 
-func worker(id int, tinygo *string, tasks <-chan string, results chan<- BuildResult, wg *sync.WaitGroup) {
-	defer wg.Done()
+// Track set of passing, failing, and excluded commands
+type BuildStatus struct {
+	passing  []string
+	failing  []string
+	excluded []string
+	modified []string
+}
+
+type WorkerResult struct {
+	dir string
+	buildRes BuildRes
+	didWork  bool // whether files in the package need(ed) constraint update
+	err error
+}
+
+func worker(id int, conf *Config, tasks <-chan string, results chan<- WorkerResult, workGroup *sync.WaitGroup) {
+	defer workGroup.Done()
 	for dir := range tasks {
-		code, err := build(id, tinygo, dir)
-		// Send the result back to the main routine
-		results <- BuildResult {
-			dir:      dir,
-			code:      code,
-			err:      err,
+		br, err := build(id, &conf.tinygo, dir)
+		var dw bool
+		if err == nil && !br.excluded {
+			dw, err = fixupPkgConstraints(dir, br.err == nil, conf.checkOnly)
+		}
+
+		// send result back to main routine
+		results <- WorkerResult {
+			dir: dir,
+			buildRes: br,
+			didWork: dw,
+			err: err,
 		}
 	}
 }
 
 // "tinygo build" in each of directories 'dirs'
-func buildDirs(tinygo *string, nWorkers int, dirs []string) (status BuildStatus, err error) {
-	if nWorkers <= 0 {
+func buildDirs(conf *Config) (status BuildStatus, err error) {
+	jobs := len(conf.dirs)
+	nWorkers := conf.nWorkers
+	if conf.nWorkers <= 0 {
 		nWorkers = runtime.NumCPU()
 	}
+	if nWorkers > jobs {
+		nWorkers = jobs
+	}
 	tasks := make(chan string)
-	results := make(chan BuildResult)
+	results := make(chan WorkerResult)
 	var wg sync.WaitGroup
 
 	// Start workers
 	log.Printf("Spawning %v workers", nWorkers)
 	for id := 0; id < nWorkers; id++ {
 		wg.Add(1)
-		go worker(id, tinygo, tasks, results, &wg)
+		go worker(id+1, conf, tasks, results, &wg)
 	}
 
 	// Assign tasks
 	go func() {
-		for _, dir := range dirs {
+		for _, dir := range conf.dirs {
 			tasks <- dir
 		}
 		close(tasks) // close channel signals workers to exit when done
@@ -87,99 +113,52 @@ func buildDirs(tinygo *string, nWorkers int, dirs []string) (status BuildStatus,
 		close(results) // close results channel after all workers done
 	}()
 
+	nComplete := 0
 	for result := range results {
+		nComplete += 1
+		progress(nComplete, jobs)
+
 		if result.err != nil {
 			break
 		}
-		switch result.code {
-			case BuildCodeExclude:
-				status.excluded = append(status.excluded, result.dir)
-			case BuildCodeFailed:
-				status.failing = append(status.failing, result.dir)
-			case BuildCodeSuccess:
-				status.passing = append(status.passing, result.dir)
-		}
-	}
-	return
-}
-
-func writeMarkdown(file *os.File, pathMD *string, tgVersion *string, status BuildStatus) (err error) {
-	// (not string literal because conflict with markdown back-tick)
-	fmt.Fprintf(file, "---\n\n")
-	fmt.Fprintf(file, "DO NOT EDIT.\n\n")
-	fmt.Fprintf(file, "Generated via `go run tools/tinygoize/main.go`\n\n")
-	fmt.Fprintf(file, "%v\n\n", *tgVersion)
-	fmt.Fprintf(file, "---\n\n")
-
-	fmt.Fprintf(file, `# Status of u-root + tinygo
-This document aims to track the process of enabling all u-root commands
-to be built using tinygo. It will be updated as more commands can be built via:
-
-    u-root> go run tools/tinygoize/* cmds/{core,exp,extra}/*
-
-Commands that cannot be built with tinygo have a \"(!tinygo || tinygo.enable)\"
-build constraint. Specify the "tinygo.enable" build tag to attempt to build
-them.
-
-    tinygo build -tags tinygo.enable cmds/core/ls
-
-The list below is the result of building each command for Linux, x86_64.
-
-The necessary additions to tinygo will be tracked in
-[#2979](https://github.com/u-root/u-root/issues/2979).
-
----
-
-## Commands Build Status
-`)
-
-	linkText := func(dir string) string {
-		// ignoring err here because pathMD already opened(exists) and
-		// dir already checked
-		relPath, _ := filepath.Rel(filepath.Dir(*pathMD), dir)
-		return fmt.Sprintf("[%v](%v)", dir, relPath)
-	}
-
-	processSet := func(header string, dirs []string) {
-		fmt.Fprintf(file, "\n### %v (%v commands)\n", header, len(dirs))
-		sort.Strings(dirs)
-
-		if len(dirs) == 0 {
-			fmt.Fprintf(file, "NONE\n")
+		if result.buildRes.excluded {
+			status.excluded = append(status.excluded, result.dir)
+		} else if result.buildRes.err != nil {
+			status.failing = append(status.failing, result.dir)
+		} else {
+			status.passing = append(status.passing, result.dir)
 		}
-		for _, dir := range dirs {
-			msg := fmt.Sprintf(" - %v", linkText(dir))
-			tags := buildTags(dir)
-			if len(tags) > 0 {
-				msg += fmt.Sprintf(" tags: %v", tags)
-			}
-			fmt.Fprintf(file, "%v\n", msg)
+		if result.didWork {
+			status.modified = append(status.modified, result.dir)
 		}
 	}
-
-	processSet("EXCLUDED", status.excluded)
-	processSet("FAILING", status.failing)
-	processSet("PASSING", status.passing)
-
 	return
 }
 
 func main() {
-	pathMD := flag.String("o", "-", "Output file for markdown summary, '-' or '' for STDOUT")
-	tinygo := flag.String("tinygo", "tinygo", "Path to tinygo")
-	nWorkers := flag.Int("j", 0, "Allow 'j' jobs at once; NumCPU() jobs with no arg.")
+	conf := Config{}
+	flag.StringVar(&conf.pathMD, "o", "-", "Output file for markdown summary, '-' or '' for STDOUT")
+	flag.StringVar(&conf.tinygo, "tinygo", "tinygo", "Path to tinygo")
+	flag.IntVar(&conf.nWorkers, "j", 0, "Allow 'j' jobs at once; NumCPU() jobs with no arg.")
+	flag.BoolVar(&conf.checkOnly, "n", false, "Check-only, do not modify sources")
+	flag.BoolVar(&conf.verbose, "v", false, "Verbose")
 
 	flag.Parse()
+	conf.dirs = flag.Args()
+
+	if !conf.verbose {
+		log.SetOutput(io.Discard)
+	}
 
-	tgVersion, err := tinygoVersion(tinygo)
+	tgVersion, err := tinygoVersion(&conf.tinygo)
 	if err != nil {
 		log.Fatal(err)
 	}
 	log.Printf("%s\n", tgVersion)
 
 	file := os.Stdout
-	if len(*pathMD) > 0 && *pathMD != "-" {
-		file, err = os.Create(*pathMD)
+	if len(conf.pathMD) > 0 && conf.pathMD != "-" {
+		file, err = os.Create(conf.pathMD)
 		if err != nil {
 			fmt.Printf("Error creating opening file: %v\n", err)
 			os.Exit(1)
@@ -188,30 +167,46 @@ func main() {
 	}
 
 	// generate list of commands that pass / fail / are excluded
-	status, err := buildDirs(tinygo, *nWorkers, flag.Args())
+	status, err := buildDirs(&conf)
 	if nil != err {
 		log.Fatal(err)
 	}
 
 	// fix-up constraints in failing files
-	for _, f := range status.failing {
-		err = fixupConstraints(f, false)
-		if nil != err {
-			log.Fatal(err)
-		}
-	}
-
-	// fix-up constraints in passing files
-	for _, f := range status.passing {
-		err = fixupConstraints(f, true)
-		if nil != err {
-			log.Fatal(err)
-		}
-	}
+	// for _, f := range status.failing {
+	// 	dw, err := fixupPkgConstraints(f, false, conf.checkOnly)
+	// 	if nil != err {
+	// 		log.Fatal(err)
+	// 	}
+	// 	if dw {
+	// 		modified = append(modified, f)
+	// 	}
+	// }
+
+	// // fix-up constraints in passing files
+	// for _, f := range status.passing {
+	// 	dw, err := fixupPkgConstraints(f, true, conf.checkOnly)
+	// 	if nil != err {
+	// 		log.Fatal(err)
+	// 	}
+	// 	if dw {
+	// 		modified = append(modified, f)
+	// 	}
+	// }
 
 	// write markdown output
-	err = writeMarkdown(file, pathMD, &tgVersion, status)
+	err = writeMarkdown(file, &conf.pathMD, &tgVersion, status)
 	if nil != err {
 		log.Fatal(err)
 	}
+
+	if len(status.modified) > 0 {
+		fmt.Println("Updates required in package(s):")
+		for _,modded := range status.modified {
+			fmt.Println(modded)
+		}
+		os.Exit(1)
+	} else {
+		fmt.Println("Build constraints up to date.")
+	}
 }
diff --git a/tools/tinygoize/markdown.go b/tools/tinygoize/markdown.go
new file mode 100644
index 0000000000..9093197f52
--- /dev/null
+++ b/tools/tinygoize/markdown.go
@@ -0,0 +1,70 @@
+package main
+
+import (
+	"fmt"
+	"path/filepath"
+	"sort"
+	"os"
+)
+
+func writeMarkdown(file *os.File, pathMD *string, tgVersion *string, status BuildStatus) (err error) {
+	// (not string literal because conflict with markdown back-tick)
+	fmt.Fprintf(file, "---\n\n")
+	fmt.Fprintf(file, "DO NOT EDIT.\n\n")
+	fmt.Fprintf(file, "Generated via `go run tools/tinygoize/main.go`\n\n")
+	fmt.Fprintf(file, "%v\n\n", *tgVersion)
+	fmt.Fprintf(file, "---\n\n")
+
+	fmt.Fprintf(file, `# Status of u-root + tinygo
+This document aims to track the process of enabling all u-root commands
+to be built using tinygo. It will be updated as more commands can be built via:
+
+    u-root> go run tools/tinygoize/* cmds/{core,exp,extra}/*
+
+Commands that cannot be built with tinygo have a \"(!tinygo || tinygo.enable)\"
+build constraint. Specify the "tinygo.enable" build tag to attempt to build
+them.
+
+    tinygo build -tags tinygo.enable cmds/core/ls
+
+The list below is the result of building each command for Linux, x86_64.
+
+The necessary additions to tinygo will be tracked in
+[#2979](https://github.com/u-root/u-root/issues/2979).
+
+---
+
+## Commands Build Status
+`)
+
+	linkText := func(dir string) string {
+		// ignoring err here because pathMD already opened(exists) and
+		// dir already checked
+		relPath, _ := filepath.Rel(filepath.Dir(*pathMD), dir)
+		return fmt.Sprintf("[%v](%v)", dir, relPath)
+	}
+
+	processSet := func(header string, dirs []string) {
+		fmt.Fprintf(file, "\n### %v (%v commands)\n", header, len(dirs))
+		sort.Strings(dirs)
+
+		if len(dirs) == 0 {
+			fmt.Fprintf(file, "NONE\n")
+		}
+		for _, dir := range dirs {
+			msg := fmt.Sprintf(" - %v", linkText(dir))
+			tags := buildTags(dir)
+			if len(tags) > 0 {
+				msg += fmt.Sprintf(" tags: %v", tags)
+			}
+			fmt.Fprintf(file, "%v\n", msg)
+		}
+	}
+
+	processSet("EXCLUDED", status.excluded)
+	processSet("FAILING", status.failing)
+	processSet("PASSING", status.passing)
+
+	return
+}
+