diff --git a/cmd/tipgodoc/Dockerfile b/cmd/tip/Dockerfile
similarity index 63%
rename from cmd/tipgodoc/Dockerfile
rename to cmd/tip/Dockerfile
index 760ca0bb..8364cdb8 100644
--- a/cmd/tipgodoc/Dockerfile
+++ b/cmd/tip/Dockerfile
@@ -1,13 +1,13 @@
-FROM golang:1.4.2
+FROM golang:1.5
 
 RUN apt-get update && apt-get install --no-install-recommends -y -q build-essential git
 
 # golang puts its go install here (weird but true)
-ENV GOROOT_BOOTSTRAP /usr/src/go
+ENV GOROOT_BOOTSTRAP /usr/local/go
 
 # golang sets GOPATH=/go
-ADD . /go/src/tipgodoc
-RUN go install tipgodoc
-ENTRYPOINT ["/go/bin/tipgodoc"]
+ADD . /go/src/tip
+RUN go install tip
+ENTRYPOINT ["/go/bin/tip"]
 # Kubernetes expects us to listen on port 8080
 EXPOSE 8080 
diff --git a/cmd/tip/README b/cmd/tip/README
new file mode 100644
index 00000000..098755ce
--- /dev/null
+++ b/cmd/tip/README
@@ -0,0 +1,3 @@
+To deploy tip.golang.org:
+
+$ gcloud --project golang-org preview app deploy --set-default godoc.yaml
diff --git a/cmd/tip/godoc.go b/cmd/tip/godoc.go
new file mode 100644
index 00000000..99f770ec
--- /dev/null
+++ b/cmd/tip/godoc.go
@@ -0,0 +1,88 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"time"
+)
+
+type godocBuilder struct {
+}
+
+func (b godocBuilder) Signature(heads map[string]string) string {
+	return heads["go"] + "-" + heads["tools"]
+}
+
+var indexingMsg = []byte("Indexing in progress: result may be inaccurate")
+
+func (b godocBuilder) Init(dir, hostport string, heads map[string]string) (*exec.Cmd, error) {
+	goDir := filepath.Join(dir, "go")
+	toolsDir := filepath.Join(dir, "gopath/src/golang.org/x/tools")
+	if err := checkout(repoURL+"go", heads["go"], goDir); err != nil {
+		return nil, err
+	}
+	if err := checkout(repoURL+"tools", heads["tools"], toolsDir); err != nil {
+		return nil, err
+	}
+
+	make := exec.Command(filepath.Join(goDir, "src/make.bash"))
+	make.Dir = filepath.Join(goDir, "src")
+	if err := runErr(make); err != nil {
+		return nil, err
+	}
+	goBin := filepath.Join(goDir, "bin/go")
+	install := exec.Command(goBin, "install", "golang.org/x/tools/cmd/godoc")
+	install.Env = []string{
+		"GOROOT=" + goDir,
+		"GOPATH=" + filepath.Join(dir, "gopath"),
+		"GOROOT_BOOTSTRAP=" + os.Getenv("GOROOT_BOOTSTRAP"),
+	}
+	if err := runErr(install); err != nil {
+		return nil, err
+	}
+
+	godocBin := filepath.Join(goDir, "bin/godoc")
+	godoc := exec.Command(godocBin, "-http="+hostport, "-index", "-index_interval=-1s")
+	godoc.Env = []string{"GOROOT=" + goDir}
+	// TODO(adg): log this somewhere useful
+	godoc.Stdout = os.Stdout
+	godoc.Stderr = os.Stderr
+	if err := godoc.Start(); err != nil {
+		return nil, err
+	}
+	go func() {
+		// TODO(bradfitz): tell the proxy that this side is dead
+		if err := godoc.Wait(); err != nil {
+			log.Printf("process in %v exited: %v", dir, err)
+		}
+	}()
+
+	var err error
+	deadline := time.Now().Add(startTimeout)
+	for time.Now().Before(deadline) {
+		time.Sleep(time.Second)
+		var res *http.Response
+		res, err = http.Get(fmt.Sprintf("http://%v/search?q=FALLTHROUGH", hostport))
+		if err != nil {
+			continue
+		}
+		rbody, err := ioutil.ReadAll(res.Body)
+		res.Body.Close()
+		if err == nil && res.StatusCode == http.StatusOK &&
+			!bytes.Contains(rbody, indexingMsg) {
+			return godoc, nil
+		}
+	}
+	godoc.Process.Kill()
+	return nil, fmt.Errorf("timed out waiting for process in %v at %v (%v)", dir, hostport, err)
+}
diff --git a/cmd/tipgodoc/app.yaml b/cmd/tip/godoc.yaml
similarity index 80%
rename from cmd/tipgodoc/app.yaml
rename to cmd/tip/godoc.yaml
index f5d68943..93d0ec63 100644
--- a/cmd/tipgodoc/app.yaml
+++ b/cmd/tip/godoc.yaml
@@ -10,3 +10,6 @@ automatic_scaling:
 handlers:
 - url: /.*
   script: _go_app
+
+env_variables:
+  TIP_BUILDER: 'godoc'
diff --git a/cmd/tipgodoc/tip.go b/cmd/tip/tip.go
similarity index 66%
rename from cmd/tipgodoc/tip.go
rename to cmd/tip/tip.go
index 833c0d01..4b897a2d 100644
--- a/cmd/tipgodoc/tip.go
+++ b/cmd/tip/tip.go
@@ -8,7 +8,6 @@ package main
 
 import (
 	"bufio"
-	"bytes"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -30,10 +29,17 @@ const (
 	startTimeout = 5 * time.Minute
 )
 
-var indexingMsg = []byte("Indexing in progress: result may be inaccurate")
-
 func main() {
-	p := new(Proxy)
+	const k = "TIP_BUILDER"
+	var b Builder
+	switch os.Getenv(k) {
+	case "godoc":
+		b = godocBuilder{}
+	default:
+		log.Fatalf("Unknown %v value: %q", k, os.Getenv(k))
+	}
+
+	p := &Proxy{builder: b}
 	go p.run()
 	http.Handle("/", p)
 
@@ -46,6 +52,8 @@ func main() {
 // Proxy implements the tip.golang.org server: a reverse-proxy
 // that builds and runs godoc instances showing the latest docs.
 type Proxy struct {
+	builder Builder
+
 	mu    sync.Mutex // protects the followin'
 	proxy http.Handler
 	cur   string    // signature of gorepo+toolsrepo
@@ -54,6 +62,11 @@ type Proxy struct {
 	err   error
 }
 
+type Builder interface {
+	Signature(heads map[string]string) string
+	Init(dir, hostport string, heads map[string]string) (*exec.Cmd, error)
+}
+
 func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if r.URL.Path == "/_tipstatus" {
 		p.serveStatus(w, r)
@@ -64,7 +77,7 @@ func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	err := p.err
 	p.mu.Unlock()
 	if proxy == nil {
-		s := "tip.golang.org is starting up"
+		s := "starting up"
 		if err != nil {
 			s = err.Error()
 		}
@@ -108,7 +121,7 @@ func (p *Proxy) poll() {
 		return
 	}
 
-	sig := heads["go"] + "-" + heads["tools"]
+	sig := p.builder.Signature(heads)
 
 	p.mu.Lock()
 	changes := sig != p.cur
@@ -125,7 +138,16 @@ func (p *Proxy) poll() {
 		newSide = "a"
 	}
 
-	cmd, hostport, err := initSide(newSide, heads["go"], heads["tools"])
+	dir := filepath.Join(os.TempDir(), "tip", newSide)
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		p.err = err
+		return
+	}
+	hostport := "localhost:8081"
+	if newSide == "b" {
+		hostport = "localhost:8082"
+	}
+	cmd, err := p.builder.Init(dir, hostport, heads)
 
 	p.mu.Lock()
 	defer p.mu.Unlock()
@@ -149,76 +171,6 @@ func (p *Proxy) poll() {
 	p.cmd = cmd
 }
 
-func initSide(side, goHash, toolsHash string) (godoc *exec.Cmd, hostport string, err error) {
-	dir := filepath.Join(os.TempDir(), "tipgodoc", side)
-	if err := os.MkdirAll(dir, 0755); err != nil {
-		return nil, "", err
-	}
-
-	goDir := filepath.Join(dir, "go")
-	toolsDir := filepath.Join(dir, "gopath/src/golang.org/x/tools")
-	if err := checkout(repoURL+"go", goHash, goDir); err != nil {
-		return nil, "", err
-	}
-	if err := checkout(repoURL+"tools", toolsHash, toolsDir); err != nil {
-		return nil, "", err
-	}
-
-	make := exec.Command(filepath.Join(goDir, "src/make.bash"))
-	make.Dir = filepath.Join(goDir, "src")
-	if err := runErr(make); err != nil {
-		return nil, "", err
-	}
-	goBin := filepath.Join(goDir, "bin/go")
-	install := exec.Command(goBin, "install", "golang.org/x/tools/cmd/godoc")
-	install.Env = []string{
-		"GOROOT=" + goDir,
-		"GOPATH=" + filepath.Join(dir, "gopath"),
-		"GOROOT_BOOTSTRAP=" + os.Getenv("GOROOT_BOOTSTRAP"),
-	}
-	if err := runErr(install); err != nil {
-		return nil, "", err
-	}
-
-	godocBin := filepath.Join(goDir, "bin/godoc")
-	hostport = "localhost:8081"
-	if side == "b" {
-		hostport = "localhost:8082"
-	}
-	godoc = exec.Command(godocBin, "-http="+hostport, "-index", "-index_interval=-1s")
-	godoc.Env = []string{"GOROOT=" + goDir}
-	// TODO(adg): log this somewhere useful
-	godoc.Stdout = os.Stdout
-	godoc.Stderr = os.Stderr
-	if err := godoc.Start(); err != nil {
-		return nil, "", err
-	}
-	go func() {
-		// TODO(bradfitz): tell the proxy that this side is dead
-		if err := godoc.Wait(); err != nil {
-			log.Printf("side %v exited: %v", side, err)
-		}
-	}()
-
-	deadline := time.Now().Add(startTimeout)
-	for time.Now().Before(deadline) {
-		time.Sleep(time.Second)
-		var res *http.Response
-		res, err = http.Get(fmt.Sprintf("http://%v/search?q=FALLTHROUGH", hostport))
-		if err != nil {
-			continue
-		}
-		rbody, err := ioutil.ReadAll(res.Body)
-		res.Body.Close()
-		if err == nil && res.StatusCode == http.StatusOK &&
-			!bytes.Contains(rbody, indexingMsg) {
-			return godoc, hostport, nil
-		}
-	}
-	godoc.Process.Kill()
-	return nil, "", fmt.Errorf("timed out waiting for side %v at %v (%v)", side, hostport, err)
-}
-
 func runErr(cmd *exec.Cmd) error {
 	out, err := cmd.CombinedOutput()
 	if err != nil {
diff --git a/cmd/tipgodoc/README b/cmd/tipgodoc/README
deleted file mode 100644
index 76ab9bdf..00000000
--- a/cmd/tipgodoc/README
+++ /dev/null
@@ -1,3 +0,0 @@
-To deploy as an App Engine Manged VM, use gcloud:
-
-$ gcloud --project golang-org preview app deploy --set-default app.yaml