diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index af1ee396841..e0973acbf45 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -1032,6 +1032,7 @@
 //
 // 	download    download modules to local cache
 // 	edit        edit go.mod from tools or scripts
+// 	editwork    edit go.work from tools or scripts
 // 	graph       print module requirement graph
 // 	init        initialize new module in current directory
 // 	initwork    initialize workspace file
@@ -1191,6 +1192,77 @@
 // See https://golang.org/ref/mod#go-mod-edit for more about 'go mod edit'.
 //
 //
+// Edit go.work from tools or scripts
+//
+// Usage:
+//
+// 	go mod editwork [editing flags] [go.work]
+//
+// Editwork provides a command-line interface for editing go.work,
+// for use primarily by tools or scripts. It only reads go.work;
+// it does not look up information about the modules involved.
+// If no file is specified, editwork looks for a go.work file in the current
+// directory and its parent directories
+//
+// The editing flags specify a sequence of editing operations.
+//
+// The -fmt flag reformats the go.work file without making other changes.
+// This reformatting is also implied by any other modifications that use or
+// rewrite the go.mod file. The only time this flag is needed is if no other
+// flags are specified, as in 'go mod editwork -fmt'.
+//
+// The -directory=path and -dropdirectory=path flags
+// add and drop a directory from the go.work files set of module directories.
+//
+// The -replace=old[@v]=new[@v] flag adds a replacement of the given
+// module path and version pair. If the @v in old@v is omitted, a
+// replacement without a version on the left side is added, which applies
+// to all versions of the old module path. If the @v in new@v is omitted,
+// the new path should be a local module root directory, not a module
+// path. Note that -replace overrides any redundant replacements for old[@v],
+// so omitting @v will drop existing replacements for specific versions.
+//
+// The -dropreplace=old[@v] flag drops a replacement of the given
+// module path and version pair. If the @v is omitted, a replacement without
+// a version on the left side is dropped.
+//
+// The -directory, -dropdirectory, -replace, and -dropreplace,
+// editing flags may be repeated, and the changes are applied in the order given.
+//
+// The -go=version flag sets the expected Go language version.
+//
+// The -print flag prints the final go.work in its text format instead of
+// writing it back to go.mod.
+//
+// The -json flag prints the final go.work file in JSON format instead of
+// writing it back to go.mod. The JSON output corresponds to these Go types:
+//
+// 	type Module struct {
+// 		Path    string
+// 		Version string
+// 	}
+//
+// 	type GoWork struct {
+// 		Go        string
+// 		Directory []Directory
+// 		Replace   []Replace
+// 	}
+//
+// 	type Directory struct {
+// 		Path       string
+// 		ModulePath string
+// 	}
+//
+// 	type Replace struct {
+// 		Old Module
+// 		New Module
+// 	}
+//
+// See the workspaces design proposal at
+// https://go.googlesource.com/proposal/+/master/design/45713-workspace.md for
+// more information.
+//
+//
 // Print module requirement graph
 //
 // Usage:
diff --git a/src/cmd/go/internal/modcmd/editwork.go b/src/cmd/go/internal/modcmd/editwork.go
new file mode 100644
index 00000000000..f05d9245e7d
--- /dev/null
+++ b/src/cmd/go/internal/modcmd/editwork.go
@@ -0,0 +1,282 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// go mod editwork
+
+package modcmd
+
+import (
+	"bytes"
+	"cmd/go/internal/base"
+	"cmd/go/internal/lockedfile"
+	"cmd/go/internal/modload"
+	"context"
+	"encoding/json"
+	"errors"
+	"os"
+	"strings"
+
+	"golang.org/x/mod/modfile"
+)
+
+var cmdEditwork = &base.Command{
+	UsageLine: "go mod editwork [editing flags] [go.work]",
+	Short:     "edit go.work from tools or scripts",
+	Long: `Editwork provides a command-line interface for editing go.work,
+for use primarily by tools or scripts. It only reads go.work;
+it does not look up information about the modules involved.
+If no file is specified, editwork looks for a go.work file in the current
+directory and its parent directories
+
+The editing flags specify a sequence of editing operations.
+
+The -fmt flag reformats the go.work file without making other changes.
+This reformatting is also implied by any other modifications that use or
+rewrite the go.mod file. The only time this flag is needed is if no other
+flags are specified, as in 'go mod editwork -fmt'.
+
+The -directory=path and -dropdirectory=path flags
+add and drop a directory from the go.work files set of module directories.
+
+The -replace=old[@v]=new[@v] flag adds a replacement of the given
+module path and version pair. If the @v in old@v is omitted, a
+replacement without a version on the left side is added, which applies
+to all versions of the old module path. If the @v in new@v is omitted,
+the new path should be a local module root directory, not a module
+path. Note that -replace overrides any redundant replacements for old[@v],
+so omitting @v will drop existing replacements for specific versions.
+
+The -dropreplace=old[@v] flag drops a replacement of the given
+module path and version pair. If the @v is omitted, a replacement without
+a version on the left side is dropped.
+
+The -directory, -dropdirectory, -replace, and -dropreplace,
+editing flags may be repeated, and the changes are applied in the order given.
+
+The -go=version flag sets the expected Go language version.
+
+The -print flag prints the final go.work in its text format instead of
+writing it back to go.mod.
+
+The -json flag prints the final go.work file in JSON format instead of
+writing it back to go.mod. The JSON output corresponds to these Go types:
+
+	type Module struct {
+		Path    string
+		Version string
+	}
+
+	type GoWork struct {
+		Go        string
+		Directory []Directory
+		Replace   []Replace
+	}
+
+	type Directory struct {
+		Path       string
+		ModulePath string
+	}
+
+	type Replace struct {
+		Old Module
+		New Module
+	}
+
+See the workspaces design proposal at
+https://go.googlesource.com/proposal/+/master/design/45713-workspace.md for
+more information.
+`,
+}
+
+var (
+	editworkFmt   = cmdEditwork.Flag.Bool("fmt", false, "")
+	editworkGo    = cmdEditwork.Flag.String("go", "", "")
+	editworkJSON  = cmdEditwork.Flag.Bool("json", false, "")
+	editworkPrint = cmdEditwork.Flag.Bool("print", false, "")
+	workedits     []func(file *modfile.WorkFile) // edits specified in flags
+)
+
+func init() {
+	cmdEditwork.Run = runEditwork // break init cycle
+
+	cmdEditwork.Flag.Var(flagFunc(flagEditworkDirectory), "directory", "")
+	cmdEditwork.Flag.Var(flagFunc(flagEditworkDropDirectory), "dropdirectory", "")
+	cmdEditwork.Flag.Var(flagFunc(flagEditworkReplace), "replace", "")
+	cmdEditwork.Flag.Var(flagFunc(flagEditworkDropReplace), "dropreplace", "")
+
+	base.AddWorkfileFlag(&cmdEditwork.Flag)
+}
+
+func runEditwork(ctx context.Context, cmd *base.Command, args []string) {
+	anyFlags :=
+		*editworkGo != "" ||
+			*editworkJSON ||
+			*editworkPrint ||
+			*editworkFmt ||
+			len(workedits) > 0
+
+	if !anyFlags {
+		base.Fatalf("go mod edit: no flags specified (see 'go help mod edit').")
+	}
+
+	if *editworkJSON && *editworkPrint {
+		base.Fatalf("go mod edit: cannot use both -json and -print")
+	}
+
+	if len(args) > 1 {
+		base.Fatalf("go mod edit: too many arguments")
+	}
+	var gowork string
+	if len(args) == 1 {
+		gowork = args[0]
+	} else {
+		modload.InitWorkfile()
+		gowork = modload.WorkFilePath()
+	}
+
+	if *editworkGo != "" {
+		if !modfile.GoVersionRE.MatchString(*editworkGo) {
+			base.Fatalf(`go mod: invalid -go option; expecting something like "-go %s"`, modload.LatestGoVersion())
+		}
+	}
+
+	data, err := lockedfile.Read(gowork)
+	if err != nil {
+		base.Fatalf("go: %v", err)
+	}
+
+	workFile, err := modfile.ParseWork(gowork, data, nil)
+	if err != nil {
+		base.Fatalf("go: errors parsing %s:\n%s", base.ShortPath(gowork), err)
+	}
+
+	if *editworkGo != "" {
+		if err := workFile.AddGoStmt(*editworkGo); err != nil {
+			base.Fatalf("go: internal error: %v", err)
+		}
+	}
+
+	if len(workedits) > 0 {
+		for _, edit := range workedits {
+			edit(workFile)
+		}
+	}
+	workFile.SortBlocks()
+	workFile.Cleanup() // clean file after edits
+
+	if *editworkJSON {
+		editworkPrintJSON(workFile)
+		return
+	}
+
+	out := modfile.Format(workFile.Syntax)
+
+	if *editworkPrint {
+		os.Stdout.Write(out)
+		return
+	}
+
+	err = lockedfile.Transform(gowork, func(lockedData []byte) ([]byte, error) {
+		if !bytes.Equal(lockedData, data) {
+			return nil, errors.New("go.work changed during editing; not overwriting")
+		}
+		return out, nil
+	})
+	if err != nil {
+		base.Fatalf("go: %v", err)
+	}
+}
+
+// flagEditworkDirectory implements the -directory flag.
+func flagEditworkDirectory(arg string) {
+	workedits = append(workedits, func(f *modfile.WorkFile) {
+		if err := f.AddDirectory(arg, ""); err != nil {
+			base.Fatalf("go mod: -directory=%s: %v", arg, err)
+		}
+	})
+}
+
+// flagEditworkDropDirectory implements the -dropdirectory flag.
+func flagEditworkDropDirectory(arg string) {
+	workedits = append(workedits, func(f *modfile.WorkFile) {
+		if err := f.DropDirectory(arg); err != nil {
+			base.Fatalf("go mod: -dropdirectory=%s: %v", arg, err)
+		}
+	})
+}
+
+// flagReplace implements the -replace flag.
+func flagEditworkReplace(arg string) {
+	var i int
+	if i = strings.Index(arg, "="); i < 0 {
+		base.Fatalf("go mod: -replace=%s: need old[@v]=new[@w] (missing =)", arg)
+	}
+	old, new := strings.TrimSpace(arg[:i]), strings.TrimSpace(arg[i+1:])
+	if strings.HasPrefix(new, ">") {
+		base.Fatalf("go mod: -replace=%s: separator between old and new is =, not =>", arg)
+	}
+	oldPath, oldVersion, err := parsePathVersionOptional("old", old, false)
+	if err != nil {
+		base.Fatalf("go mod: -replace=%s: %v", arg, err)
+	}
+	newPath, newVersion, err := parsePathVersionOptional("new", new, true)
+	if err != nil {
+		base.Fatalf("go mod: -replace=%s: %v", arg, err)
+	}
+	if newPath == new && !modfile.IsDirectoryPath(new) {
+		base.Fatalf("go mod: -replace=%s: unversioned new path must be local directory", arg)
+	}
+
+	workedits = append(workedits, func(f *modfile.WorkFile) {
+		if err := f.AddReplace(oldPath, oldVersion, newPath, newVersion); err != nil {
+			base.Fatalf("go mod: -replace=%s: %v", arg, err)
+		}
+	})
+}
+
+// flagDropReplace implements the -dropreplace flag.
+func flagEditworkDropReplace(arg string) {
+	path, version, err := parsePathVersionOptional("old", arg, true)
+	if err != nil {
+		base.Fatalf("go mod: -dropreplace=%s: %v", arg, err)
+	}
+	workedits = append(workedits, func(f *modfile.WorkFile) {
+		if err := f.DropReplace(path, version); err != nil {
+			base.Fatalf("go mod: -dropreplace=%s: %v", arg, err)
+		}
+	})
+}
+
+// editPrintJSON prints the -json output.
+func editworkPrintJSON(workFile *modfile.WorkFile) {
+	var f workfileJSON
+	if workFile.Go != nil {
+		f.Go = workFile.Go.Version
+	}
+	for _, d := range workFile.Directory {
+		f.Directory = append(f.Directory, directoryJSON{DiskPath: d.Path, ModPath: d.ModulePath})
+	}
+
+	for _, r := range workFile.Replace {
+		f.Replace = append(f.Replace, replaceJSON{r.Old, r.New})
+	}
+	data, err := json.MarshalIndent(&f, "", "\t")
+	if err != nil {
+		base.Fatalf("go: internal error: %v", err)
+	}
+	data = append(data, '\n')
+	os.Stdout.Write(data)
+}
+
+// workfileJSON is the -json output data structure.
+type workfileJSON struct {
+	Go        string `json:",omitempty"`
+	Directory []directoryJSON
+	Replace   []replaceJSON
+}
+
+type directoryJSON struct {
+	DiskPath string
+	ModPath  string `json:",omitempty"`
+}
diff --git a/src/cmd/go/internal/modcmd/mod.go b/src/cmd/go/internal/modcmd/mod.go
index 3586b44c1ad..29aad583240 100644
--- a/src/cmd/go/internal/modcmd/mod.go
+++ b/src/cmd/go/internal/modcmd/mod.go
@@ -23,6 +23,7 @@ See 'go help modules' for an overview of module functionality.
 	Commands: []*base.Command{
 		cmdDownload,
 		cmdEdit,
+		cmdEditwork,
 		cmdGraph,
 		cmdInit,
 		cmdInitwork,
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index de8adbafc44..5dd946215bf 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -249,6 +249,12 @@ func InitWorkfile() {
 	}
 }
 
+// WorkFilePath returns the path of the go.work file, or "" if not in
+// workspace mode. WorkFilePath must be called after InitWorkfile.
+func WorkFilePath() string {
+	return workFilePath
+}
+
 // Init determines whether module mode is enabled, locates the root of the
 // current module (if any), sets environment variables for Git subprocesses, and
 // configures the cfg, codehost, load, modfetch, and search packages for use
diff --git a/src/cmd/go/testdata/script/work_edit.txt b/src/cmd/go/testdata/script/work_edit.txt
new file mode 100644
index 00000000000..0717086ee7c
--- /dev/null
+++ b/src/cmd/go/testdata/script/work_edit.txt
@@ -0,0 +1,157 @@
+# Test editing go.work files.
+
+go mod initwork m
+cmp go.work go.work.want_initial
+
+go mod editwork -directory n
+cmp go.work go.work.want_directory_n
+
+go mod editwork -go 1.18
+cmp go.work go.work.want_go_118
+
+go mod editwork -dropdirectory m
+cmp go.work go.work.want_dropdirectory_m
+
+go mod editwork -replace=x.1@v1.3.0=y.1@v1.4.0 -replace='x.1@v1.4.0 = ../z'
+cmp go.work go.work.want_add_replaces
+
+go mod editwork -directory n -directory ../a -directory /b -directory c -directory c
+cmp go.work go.work.want_multidirectory
+
+go mod editwork -dropdirectory /b -dropdirectory n
+cmp go.work go.work.want_multidropdirectory
+
+go mod editwork -dropreplace='x.1@v1.4.0'
+cmp go.work go.work.want_dropreplace
+
+go mod editwork -print -go 1.19 -directory b -dropdirectory c -replace 'x.1@v1.4.0 = ../z' -dropreplace x.1 -dropreplace x.1@v1.3.0
+cmp stdout go.work.want_print
+
+go mod editwork -json -go 1.19 -directory b -dropdirectory c -replace 'x.1@v1.4.0 = ../z' -dropreplace x.1 -dropreplace x.1@v1.3.0
+cmp stdout go.work.want_json
+
+go mod editwork -print -fmt -workfile unformatted
+cmp stdout formatted
+
+-- go.work.want_initial --
+go 1.17
+
+directory m
+-- go.work.want_directory_n --
+go 1.17
+
+directory (
+	m
+	n
+)
+-- go.work.want_go_118 --
+go 1.18
+
+directory (
+	m
+	n
+)
+-- go.work.want_dropdirectory_m --
+go 1.18
+
+directory n
+-- go.work.want_add_replaces --
+go 1.18
+
+directory n
+
+replace (
+	x.1 v1.3.0 => y.1 v1.4.0
+	x.1 v1.4.0 => ../z
+)
+-- go.work.want_multidirectory --
+go 1.18
+
+directory (
+	../a
+	/b
+	c
+	n
+)
+
+replace (
+	x.1 v1.3.0 => y.1 v1.4.0
+	x.1 v1.4.0 => ../z
+)
+-- go.work.want_multidropdirectory --
+go 1.18
+
+directory (
+	../a
+	c
+)
+
+replace (
+	x.1 v1.3.0 => y.1 v1.4.0
+	x.1 v1.4.0 => ../z
+)
+-- go.work.want_dropreplace --
+go 1.18
+
+directory (
+	../a
+	c
+)
+
+replace x.1 v1.3.0 => y.1 v1.4.0
+-- go.work.want_print --
+go 1.19
+
+directory (
+	../a
+	b
+)
+
+replace x.1 v1.4.0 => ../z
+-- go.work.want_json --
+{
+	"Go": "1.19",
+	"Directory": [
+		{
+			"DiskPath": "../a"
+		},
+		{
+			"DiskPath": "b"
+		}
+	],
+	"Replace": [
+		{
+			"Old": {
+				"Path": "x.1",
+				"Version": "v1.4.0"
+			},
+			"New": {
+				"Path": "../z"
+			}
+		}
+	]
+}
+-- unformatted --
+go 1.17
+ directory (
+ a
+  b
+  c
+  )
+  replace (
+  x.1 v1.3.0 => y.1 v1.4.0
+                            x.1 v1.4.0 => ../z
+                            )
+-- formatted --
+go 1.17
+
+directory (
+	a
+	b
+	c
+)
+
+replace (
+	x.1 v1.3.0 => y.1 v1.4.0
+	x.1 v1.4.0 => ../z
+)
\ No newline at end of file