diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..d645695
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,202 @@
+
+                                 Apache License
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+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
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+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
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+      the terms of any separate license agreement you may have executed
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+   6. Trademarks. This License does not grant permission to use the trade
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+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
diff --git a/README b/README
new file mode 100644
index 0000000..e4eaa20
--- /dev/null
+++ b/README
@@ -0,0 +1,6 @@
+A collection of libraries and commands for GWT's automated build
+infrastructure.
+
+The main tool of interest is the "presubmitter" command, which
+periodically polls Gerrit for new unverified changes and runs various
+presubmit checks on them.
diff --git a/checkstyle/checkstyle.go b/checkstyle/checkstyle.go
new file mode 100644
index 0000000..fe3ac31
--- /dev/null
+++ b/checkstyle/checkstyle.go
@@ -0,0 +1,77 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package checkstyle provides helper methods for invoking checkstyle
+// against GWT's source code.
+package checkstyle
+
+import (
+	"encoding/xml"
+	"flag"
+	"io"
+	"log"
+	"os"
+	"os/exec"
+)
+
+var checkstylejar = flag.String("checkstylejar", "../tools/antlib/checkstyle-all-4.2.jar", "path to checkstyle jar")
+
+// Error represents a specific instance of an error reported by checkstyle.
+type Error struct {
+	Line     int    `xml:"line,attr"`
+	Severity string `xml:"severity,attr"`
+	Message  string `xml:"message,attr"`
+}
+
+// File represents a collection of checkstyle errors for a single file.
+type File struct {
+	Name   string  `xml:"name,attr"`
+	Errors []Error `xml:"error"`
+}
+
+// ReadXML reads a checkstyle XML report from reader.
+func ReadXML(reader io.Reader) ([]File, error) {
+	var res struct {
+		Files []File `xml:"file"`
+	}
+	return res.Files, xml.NewDecoder(reader).Decode(&res)
+}
+
+// Run runs checkstyle using the specified config against the specified
+// list of files and returns the style errors found.
+func Run(config string, files []string) (outfiles []File, err error) {
+	if len(files) == 0 {
+		return []File{}, nil
+	}
+
+	cmd := exec.Command("java", append([]string{"-cp", *checkstylejar,
+		"-Dcheckstyle.header.file=eclipse/settings/code-style/google.header",
+		"com.puppycrawl.tools.checkstyle.Main", "-f", "xml", "-c", config},
+		files...)...)
+	reader, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, err
+	}
+	defer reader.Close()
+	cmd.Stderr = os.Stderr
+	log.Println("running checkstyle:", cmd.Args)
+	if err = cmd.Start(); err != nil {
+		return nil, err
+	}
+	// TODO(mdempsky): Check cmd.Wait() exit code?
+	defer cmd.Wait()
+	return ReadXML(reader)
+}
diff --git a/checkstyle/checkstyle_test.go b/checkstyle/checkstyle_test.go
new file mode 100644
index 0000000..ba7e99c
--- /dev/null
+++ b/checkstyle/checkstyle_test.go
@@ -0,0 +1,58 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package checkstyle_test
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"gwt.googlesource.com/buildglue.git/checkstyle"
+)
+
+func TestReadXML(t *testing.T) {
+	input := `
+	  <checkstyle>
+	    <file name="foo">
+	      <error line="15" severity="error" message="hello"/>
+	      <error line="27" severity="warning" message="bye bye"/>
+	    </file>
+	    <file name="blorp"/>
+	    <file name="bar">
+	      <error line="42" severity="info" message="woof"/>
+	    </file>
+	  </checkstyle>
+	`
+	expect := []checkstyle.File{
+		{Name: "foo", Errors: []checkstyle.Error{
+			{Line: 15, Severity: "error", Message: "hello"},
+			{Line: 27, Severity: "warning", Message: "bye bye"},
+		}},
+		{Name: "blorp"},
+		{Name: "bar", Errors: []checkstyle.Error{
+			{Line: 42, Severity: "info", Message: "woof"},
+		}},
+	}
+
+	actual, err := checkstyle.ReadXML(strings.NewReader(input))
+	if err != nil {
+		t.Error("ReadXML returned failure:", err)
+	}
+	if fmt.Sprintf("%#v", expect) != fmt.Sprintf("%#v", actual) {
+		t.Errorf("expect %#v, actual %#v", expect, actual)
+	}
+}
diff --git a/cmd/lint/lint.go b/cmd/lint/lint.go
new file mode 100644
index 0000000..b4c9b13
--- /dev/null
+++ b/cmd/lint/lint.go
@@ -0,0 +1,30 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"flag"
+
+	"gwt.googlesource.com/buildglue.git/lint"
+)
+
+func main() {
+	flag.Parse()
+	if err := lint.Lint(flag.Arg(0)); err != nil {
+		panic(err)
+	}
+}
diff --git a/cmd/post-review/postreview.go b/cmd/post-review/postreview.go
new file mode 100644
index 0000000..8111689
--- /dev/null
+++ b/cmd/post-review/postreview.go
@@ -0,0 +1,44 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"flag"
+	"strings"
+
+	"gwt.googlesource.com/buildglue.git/gerrit"
+)
+
+var (
+	verified = flag.Int("verified", 0, "value for gerrit review verified label")
+)
+
+func main() {
+	flag.Parse()
+
+	ref, message := flag.Arg(0), flag.Arg(1)
+	if !strings.HasPrefix(ref, "refs/changes/") {
+		panic("ref doesn't start with \"refs/changes/\"")
+	}
+
+	review := gerrit.Review{Message: message}
+	if *verified != 0 {
+		review.Labels = &gerrit.Labels{Verified: *verified}
+	}
+
+	gerrit.Post(ref, review)
+}
diff --git a/cmd/presubmitter/presubmitter.go b/cmd/presubmitter/presubmitter.go
new file mode 100644
index 0000000..bcc47dc
--- /dev/null
+++ b/cmd/presubmitter/presubmitter.go
@@ -0,0 +1,101 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/*
+Presubmitter polls GWT's Gerrit server and runs presubmit checks when
+new changes are detected.
+
+To use presubmitter, you need to first setup a JSON-formatted creds file
+like:
+
+    {
+      "GerritUsername": "git-azurediamond.bash.org",
+      "GerritPassword": "hunter2",
+      "JenkinsToken": "opensesame"
+    }
+
+By default, presubmitter looks for this file at $HOME/.gwtcreds.  This
+can be changed using the -creds flag.
+
+Additionally, presubmitter expects to be run from the top-level
+directory of a GWT git repository that it can use for checking out
+uploaded changes.
+
+Lastly, presubmitter expects to find the checkstyle JAR at
+../tools/antlib/checkstyle-all-4.2.jar, but this can also be changed using
+the -checkstylejar flag.
+*/
+package main
+
+import (
+	"flag"
+	"log"
+	"sync"
+	"time"
+
+	"gwt.googlesource.com/buildglue.git/gerrit"
+	"gwt.googlesource.com/buildglue.git/jenkins"
+	"gwt.googlesource.com/buildglue.git/lint"
+)
+
+const query = "(project:gwt status:open -label:Verified=1 -label:Verified=-1 -label:Code-Review=-1 -label:Code-Review=-2 ownerin:\"Jenkins Trusted\" -age:1w) OR (project:gwt status:open -label:Verified=1 -label:Verified=-1 label:Code-Review=2 -age:1w)"
+
+const timeout = 90 * time.Minute
+
+// Running lint mutates the current directory, so we need to ensure we serialize it.
+var lintLock sync.Mutex
+
+func main() {
+	flag.Parse()
+
+	nextRetry := make(map[string]time.Time)
+	for {
+		refs, err := gerrit.Query(query)
+		if err != nil {
+			log.Println("error querying gerrit:", err)
+			time.Sleep(time.Minute)
+			continue
+		}
+		log.Println("found refs:", refs)
+
+		now := time.Now()
+		for _, ref := range refs {
+			if now.Before(nextRetry[ref]) {
+				continue
+			}
+			// TODO(mdempsky): Exponential back off.
+			nextRetry[ref] = now.Add(timeout)
+
+			log.Println("verifying ref:", ref)
+			go func(ref string) {
+				lintLock.Lock()
+				if err := lint.Lint(ref); err != nil {
+					lintLock.Unlock()
+					log.Println("lint error:", err)
+					return
+				}
+				lintLock.Unlock()
+
+				if err := jenkins.RunPresubmit(ref); err != nil {
+					log.Println("presubmit error:", err)
+					return
+				}
+			}(ref)
+		}
+
+		time.Sleep(time.Minute)
+	}
+}
diff --git a/creds/creds.go b/creds/creds.go
new file mode 100644
index 0000000..fe171e7
--- /dev/null
+++ b/creds/creds.go
@@ -0,0 +1,59 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package creds provides credentials for working with GWT build infrastructure.
+package creds
+
+import (
+	"encoding/json"
+	"flag"
+	"os"
+	"sync"
+)
+
+var credsFile = flag.String("creds", os.Getenv("HOME")+"/.gwtcreds", "path to GWT creds file")
+
+var creds struct {
+	GerritUsername string
+	GerritPassword string
+	JenkinsToken   string
+}
+
+func load() {
+	f, err := os.Open(*credsFile)
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+	if err = json.NewDecoder(f).Decode(&creds); err != nil {
+		panic(err)
+	}
+}
+
+var once sync.Once
+
+// GerritBasicAuth returns the username and password for calling Gerrit REST API
+// as Jenkins.
+func GerritBasicAuth() (string, string) {
+	once.Do(load)
+	return creds.GerritUsername, creds.GerritPassword
+}
+
+// JenkinsAuthToken returns the Jenkins auth token for triggering Jenkins builds.
+func JenkinsAuthToken() string {
+	once.Do(load)
+	return creds.JenkinsToken
+}
diff --git a/gerrit/doc.go b/gerrit/doc.go
new file mode 100644
index 0000000..1bfa631
--- /dev/null
+++ b/gerrit/doc.go
@@ -0,0 +1,18 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package gerrit provides methods for interfacing with Gerrit's REST API.
+package gerrit
diff --git a/gerrit/query.go b/gerrit/query.go
new file mode 100644
index 0000000..c044dd4
--- /dev/null
+++ b/gerrit/query.go
@@ -0,0 +1,81 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package gerrit
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+
+	"gwt.googlesource.com/buildglue.git/creds"
+)
+
+// Return a list of git references matched by the Gerrit search query q.
+//
+// See https://gerrit-review.googlesource.com/Documentation/user-search.html
+// for documentation about Gerrit search syntax.
+func Query(q string) ([]string, error) {
+	url := fmt.Sprintf("https://gwt-review.googlesource.com/a/changes/?o=CURRENT_REVISION&q=%s", url.QueryEscape(q))
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Add("Accept", "application/json")
+	req.SetBasicAuth(creds.GerritBasicAuth())
+
+	res, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+
+	return ParseRefs(res.Body)
+}
+
+// ParseRefs reads a list of Gerrit ChangeInfo entries from reader and returns
+// the refs for the current revisions.
+func ParseRefs(reader io.Reader) ([]string, error) {
+	r := bufio.NewReader(reader)
+
+	// First line of input is the XSSI guard (")]}'").
+	if _, err := r.ReadSlice('\n'); err != nil {
+		return nil, err
+	}
+
+	var changes []struct {
+		Current_revision string
+		Revisions        map[string]struct {
+			Fetch struct {
+				Http struct {
+					Ref string
+				}
+			}
+		}
+	}
+	if err := json.NewDecoder(r).Decode(&changes); err != nil {
+		return nil, err
+	}
+
+	var res []string
+	for _, change := range changes {
+		res = append(res, change.Revisions[change.Current_revision].Fetch.Http.Ref)
+	}
+	return res, nil
+}
diff --git a/gerrit/query_test.go b/gerrit/query_test.go
new file mode 100644
index 0000000..34b3e38
--- /dev/null
+++ b/gerrit/query_test.go
@@ -0,0 +1,66 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package gerrit_test
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"gwt.googlesource.com/buildglue.git/gerrit"
+)
+
+func TestParseRefs(t *testing.T) {
+	// Revelant snippet from https://gerrit-review.googlesource.com/Documentation/rest-api-changes.html#current-revision
+	input := `)]}'
+	[
+	  {
+	    "current_revision": "184ebe53805e102605d11f6b143486d15c23a09c",
+	    "revisions": {
+	      "184ebe53805e102605d11f6b143486d15c23a09c": {
+	        "fetch": {
+	          "http": {
+	            "ref": "refs/changes/97/97/1"
+	          }
+	        }
+	      }
+	    }
+	  },
+	  {
+	    "current_revision": "27cc4558b5a3d3387dd11ee2df7a117e7e581822",
+	    "revisions": {
+	      "27cc4558b5a3d3387dd11ee2df7a117e7e581822": {
+	        "fetch": {
+	          "http": {
+	            "ref": "refs/changes/99/4799/2"
+	          }
+	        }
+	      }
+	    }
+	  }
+	]
+	`
+	expect := []string{"refs/changes/97/97/1", "refs/changes/99/4799/2"}
+
+	actual, err := gerrit.ParseRefs(strings.NewReader(input))
+	if err != nil {
+		t.Error("failed to parse input:", err)
+	}
+	if fmt.Sprintf("%#v", expect) != fmt.Sprintf("%#v", actual) {
+		t.Errorf("expect %#v, actual %#v", expect, actual)
+	}
+}
diff --git a/gerrit/review.go b/gerrit/review.go
new file mode 100644
index 0000000..9f6a1b4
--- /dev/null
+++ b/gerrit/review.go
@@ -0,0 +1,84 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package gerrit
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+
+	"gwt.googlesource.com/buildglue.git/creds"
+)
+
+var (
+	dryRun = flag.Bool("dryrun", false, "write Gerrit reviews to stdout instead of posting them")
+)
+
+// Comment represents a single inline file comment.
+type Comment struct {
+	Line    int    `json:"line,omitempty"`
+	Message string `json:"message,omitempty"`
+}
+
+// Labels represents the Code-Review and Verified labels associated with a review.
+type Labels struct {
+	CodeReview int `json:"Code-Review,omitempty"`
+	Verified   int `json:"Verified,omitempty"`
+}
+
+// Review represents a complete Gerrit review post.
+type Review struct {
+	Message  string               `json:"message,omitempty"`
+	Labels   *Labels              `json:"labels,omitempty"`
+	Comments map[string][]Comment `json:"comments,omitempty"`
+}
+
+// Post publishes a review to a Gerrit review thread.
+// If the -dryrun flag is set to true, then it instead prints the review to stdout.
+func Post(ref string, review Review) error {
+	if *dryRun {
+		fmt.Printf("Review for %s:\n%#v\n", ref, review)
+		return nil
+	}
+
+	// ref is of the form "refs/changes/34/1234/7"; we want "1234" and "7".
+	path := strings.Split(ref, "/")
+	changeID, revisionID := path[3], path[4]
+	url := fmt.Sprintf("https://gwt-review.googlesource.com/a/changes/%s/revisions/%s/review", changeID, revisionID)
+
+	pr, pw := io.Pipe()
+	go func() {
+		pw.CloseWithError(json.NewEncoder(pw).Encode(review))
+	}()
+	req, err := http.NewRequest("POST", url, pr)
+	if err != nil {
+		return err
+	}
+
+	req.Header.Add("Content-Type", "application/json;charset=UTF-8")
+	req.SetBasicAuth(creds.GerritBasicAuth())
+
+	res, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+	res.Body.Close()
+	return nil
+}
diff --git a/git/git.go b/git/git.go
new file mode 100644
index 0000000..6063881
--- /dev/null
+++ b/git/git.go
@@ -0,0 +1,109 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package git provides helper methods for invoking Git commands.
+package git
+
+import (
+	"bufio"
+	"errors"
+	"io"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+)
+
+// Errors returned by this package.
+var (
+	NotOneLine = errors.New("git command output was not one line")
+)
+
+// Run invokes git with the specified arguments.
+func Run(args ...string) error {
+	cmd := exec.Command("git", args...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	return cmd.Run()
+}
+
+// Lines invokes git with the specified arguments and returns a slice of
+// the output lines.
+func Lines(args ...string) (res []string, err error) {
+	cmd := exec.Command("git", args...)
+	reader, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, err
+	}
+	defer reader.Close()
+	cmd.Stderr = os.Stderr
+	if err = cmd.Start(); err != nil {
+		return nil, err
+	}
+	defer func() {
+		errwait := cmd.Wait()
+		if err == nil {
+			err = errwait
+		}
+	}()
+	r := bufio.NewReader(reader)
+	for {
+		line, err := r.ReadString('\n')
+		if err == io.EOF {
+			break
+		} else if err != nil {
+			return nil, err
+		}
+		res = append(res, line[:len(line)-1])
+	}
+	return res, nil
+}
+
+// Lines invokes git with the specified arguments and returns a string
+// containing its single line of output.  Returns NotOneLine if the
+// git does not output a single line.
+func Line(args ...string) (string, error) {
+	lines, err := Lines(args...)
+	if err != nil {
+		return "", err
+	}
+	if len(lines) != 1 {
+		return "", NotOneLine
+	}
+	return lines[0], err
+}
+
+// Blame returns the set of line numbers from file that were added or modified
+// in Git revision rev.  Rev must be a full 20 char hex revision id.  Lines are
+// numbered from 1.
+func Blame(rev, file string) (map[int]bool, error) {
+	lines, err := Lines("blame", "--porcelain", rev+"^..", "--", file)
+	if err != nil {
+		return nil, err
+	}
+	res := make(map[int]bool)
+	for _, s := range lines {
+		if !strings.HasPrefix(s, rev+" ") {
+			continue
+		}
+		i, err := strconv.Atoi(strings.Split(s, " ")[2])
+		if err != nil {
+			return nil, err
+		}
+		res[i] = true
+	}
+	return res, nil
+}
diff --git a/jenkins/jenkins.go b/jenkins/jenkins.go
new file mode 100644
index 0000000..f4d5a60
--- /dev/null
+++ b/jenkins/jenkins.go
@@ -0,0 +1,45 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package jenkins provides helper methods for interacting with GWT's Jenkins server.
+package jenkins
+
+import (
+	"net/http"
+	"net/url"
+
+	"gwt.googlesource.com/buildglue.git/creds"
+)
+
+// RunPresubmit queues a Jenkins presubmit build.
+func RunPresubmit(ref string) error {
+	url := (&url.URL{
+		Scheme: "http",
+		Host:   "localhost:8080",
+		Path:   "/job/gwt.presubmit/buildWithParameters",
+		RawQuery: url.Values{
+			"token":  {creds.JenkinsAuthToken()},
+			"COMMIT": {ref},
+		}.Encode(),
+	}).String()
+
+	// TODO(mdempsky): Check for failed return codes?
+	resp, err := http.Get(url)
+	if err == nil {
+		resp.Body.Close()
+	}
+	return err
+}
diff --git a/lint/lint.go b/lint/lint.go
new file mode 100644
index 0000000..a3931ab
--- /dev/null
+++ b/lint/lint.go
@@ -0,0 +1,231 @@
+/*
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package lint provides helper methods for quickly running lint checks
+// against a proposed change on Gerrit.
+package lint
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"strings"
+
+	"gwt.googlesource.com/buildglue.git/checkstyle"
+	"gwt.googlesource.com/buildglue.git/gerrit"
+	"gwt.googlesource.com/buildglue.git/git"
+)
+
+// Errors that can be returned by Lint.
+var (
+	LintFailed = errors.New("commit failed lint checking")
+)
+
+// Should be kept in sync with GWT's build.xml files.
+var checks = []struct {
+	config   string
+	includes []string
+	excludes []string
+}{
+	{
+		config: "eclipse/settings/code-style/gwt-checkstyle.xml",
+		includes: []string{
+			"dev/core/src/",
+			"dev/core/super/com/google/gwt/dev/jjs/intrinsic/",
+			"user/src/",
+			"user/super/com/google/gwt/emul/",
+			"user/super/com/google/gwt/junit/translatable/",
+		},
+		excludes: []string{
+			"dev/core/src/com/google/gwt/dev/shell/remoteui/RemoteMessageProto.java",
+			"dev/core/src/com/google/gwt/dev/asm/",
+			"dev/core/src/com/google/gwt/dev/js/rhino/",
+			"dev/core/src/org/eclipse/",
+			"dev/core/src/org/apache/",
+			"user/src/javax/validation/",
+			"user/src/org/hibernate/validator/",
+		},
+	},
+	{
+		config: "eclipse/settings/code-style/gwt-checkstyle-tests.xml",
+		includes: []string{
+			"user/test/com/google/",
+			"user/test/test/",
+		},
+	},
+}
+
+// Match returns true if file is a ".java" file that starts with a string
+// from includes but does not start with any strings from excludes.
+func match(file string, includes, excludes []string) bool {
+	if !strings.HasSuffix(file, ".java") {
+		return false
+	}
+	for _, exclude := range excludes {
+		if strings.HasPrefix(file, exclude) {
+			return false
+		}
+	}
+	for _, include := range includes {
+		if strings.HasPrefix(file, include) {
+			return true
+		}
+	}
+	return false
+}
+
+// Matches returns the sublist of files that match the provided includes
+// and excludes rules.
+func matches(files, includes, excludes []string) []string {
+	res := []string{}
+	for _, file := range files {
+		if match(file, includes, excludes) {
+			res = append(res, file)
+		}
+	}
+	return res
+}
+
+type linter struct {
+	rev      string
+	comments map[string][]gerrit.Comment
+	failed   bool
+}
+
+func newLinter(rev string) *linter {
+	return &linter{
+		rev:      rev,
+		comments: make(map[string][]gerrit.Comment),
+	}
+}
+
+func (l *linter) comment(file string, line int, severity, message string) {
+	comment := gerrit.Comment{Line: line, Message: fmt.Sprintf("[%s] %s", severity, message)}
+	l.comments[file] = append(l.comments[file], comment)
+	if severity == "error" {
+		l.failed = true
+	}
+}
+
+func (l *linter) checkStyle(config string, files []string) error {
+	out, err := checkstyle.Run(config, files)
+	if err != nil {
+		log.Println("running checkstyle failed:", err)
+		return err
+	}
+	for _, file := range out {
+		if len(file.Errors) == 0 {
+			continue
+		}
+		blameable, err := git.Blame(l.rev, file.Name)
+		if err != nil {
+			return err
+		}
+		for _, err := range file.Errors {
+			if blameable[err.Line] {
+				l.comment(file.Name, err.Line, err.Severity, err.Message)
+			}
+		}
+	}
+	return nil
+}
+
+func (l *linter) checkMessage(commitmsg []string) {
+	warn := func(line int, message string) {
+		// Gerrit includes some extra header lines before the commit message.
+		// TODO(mdempsky): Is it always exactly six lines?
+		l.comment("/COMMIT_MSG", line+6, "warning", message)
+	}
+
+	if len(commitmsg) >= 1 && len(commitmsg[0]) > 50 {
+		warn(1, "Subject line should be 50 characters or fewer.")
+	}
+	if len(commitmsg) >= 3 && len(commitmsg[1]) > 0 {
+		warn(2, "Subject line and body should be separated by a blank line.")
+	}
+	for i, line := range commitmsg {
+		if i >= 2 && len(line) > 72 {
+			warn(i+1, "Commit message lines should be 72 characters or fewer.")
+			break
+		}
+	}
+}
+
+func (l *linter) review() gerrit.Review {
+	res := gerrit.Review{}
+	if l.failed {
+		res.Message = ("Oops, this change failed the fast style check! " +
+			"Please fix all errors and try again.")
+		res.Labels = &gerrit.Labels{Verified: -1}
+	} else if len(l.comments) != 0 {
+		res.Message = ("This change passed the fast style check, " +
+			"but still triggered some non-error warnings. " +
+			"Please review and fix if appropriate.")
+	} else {
+		res.Message = ("Woo hoo, this change passed the fast style check " +
+			"with ZERO new warnings! You rock!")
+	}
+	if len(l.comments) != 0 {
+		res.Comments = l.comments
+	}
+	return res
+}
+
+// Lint fetches ref from Gerrit, inspects the commit message and runs checkstyle against
+// any added or modified files, and posts a review to Gerrit with the results.
+// Returns a LintFailed error if any lint errors were found.
+func Lint(ref string) error {
+	if err := git.Run("fetch", "https://gwt.googlesource.com/gwt", ref); err != nil {
+		log.Println("fetch failed:", err)
+		return err
+	}
+	rev, err := git.Line("rev-parse", "FETCH_HEAD")
+	if err != nil {
+		return err
+	}
+	if err = git.Run("checkout", rev); err != nil {
+		return err
+	}
+	files, err := git.Lines("diff-tree", "-r", "--name-only", "--diff-filter=AM", rev+"^", rev)
+	if err != nil {
+		return err
+	}
+
+	log.Println("running lint checks")
+
+	linter := newLinter(rev)
+	for _, check := range checks {
+		if err := linter.checkStyle(check.config, matches(files, check.includes, check.excludes)); err != nil {
+			log.Println("checkstyle error:", err)
+			return err
+		}
+	}
+
+	commitmsg, err := git.Lines("show", "-s", "--pretty=format:%B", rev)
+	if err != nil {
+		return err
+	}
+	linter.checkMessage(commitmsg)
+
+	if err = gerrit.Post(ref, linter.review()); err != nil {
+		return err
+	}
+
+	if linter.failed {
+		return LintFailed
+	}
+	return nil
+}