diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java
index dbe3099..476e8cc 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/BaseServlet.java
@@ -25,6 +25,7 @@
 import static javax.servlet.http.HttpServletResponse.SC_OK;
 import static org.eclipse.jgit.util.HttpSupport.ENCODING_GZIP;
 
+import com.google.common.base.Optional;
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Maps;
@@ -102,17 +103,12 @@
   @Override
   protected void doGet(HttpServletRequest req, HttpServletResponse res)
       throws IOException, ServletException {
-    FormatType format;
-    try {
-      format = FormatType.getFormatType(req);
-    } catch (IllegalArgumentException err) {
+    Optional<FormatType> format = getFormat(req);
+    if (!format.isPresent()) {
       res.sendError(SC_BAD_REQUEST);
       return;
     }
-    if (format == DEFAULT) {
-      format = getDefaultFormat(req);
-    }
-    switch (format) {
+    switch (format.get()) {
       case HTML:
         doGetHtml(req, res);
         break;
@@ -128,6 +124,14 @@
     }
   }
 
+  protected Optional<FormatType> getFormat(HttpServletRequest req) {
+    Optional<FormatType> format = FormatType.getFormatType(req);
+    if (format.isPresent() && format.get() == DEFAULT) {
+      return Optional.of(getDefaultFormat(req));
+    }
+    return format;
+  }
+
   /**
    * @param req in-progress request.
    * @return the default {@link FormatType} used when {@code ?format=} is not
diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/FormatType.java b/gitiles-servlet/src/main/java/com/google/gitiles/FormatType.java
index 9417a4c..1d2f61c 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/FormatType.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/FormatType.java
@@ -14,6 +14,8 @@
 
 package com.google.gitiles;
 
+import com.google.common.base.Enums;
+import com.google.common.base.Optional;
 import com.google.common.base.Strings;
 import com.google.common.net.HttpHeaders;
 
@@ -28,38 +30,36 @@
 
   private static final String FORMAT_TYPE_ATTRIBUTE = FormatType.class.getName();
 
-  public static FormatType getFormatType(HttpServletRequest req) {
-    FormatType result = (FormatType) req.getAttribute(FORMAT_TYPE_ATTRIBUTE);
+  public static Optional<FormatType> getFormatType(HttpServletRequest req) {
+    @SuppressWarnings("unchecked")
+    Optional<FormatType> result =
+        (Optional<FormatType>) req.getAttribute(FORMAT_TYPE_ATTRIBUTE);
     if (result != null) {
       return result;
     }
 
-    String format = req.getParameter("format");
-    if (format != null) {
-      for (FormatType type : FormatType.values()) {
-        if (format.equalsIgnoreCase(type.name())) {
-          return set(req, type);
-        }
-      }
-      throw new IllegalArgumentException("Invalid format " + format);
+    String fmt = req.getParameter("format");
+    if (!Strings.isNullOrEmpty(fmt)) {
+      return set(req, Enums.getIfPresent(FormatType.class, fmt.toUpperCase()));
     }
 
     String accept = req.getHeader(HttpHeaders.ACCEPT);
     if (Strings.isNullOrEmpty(accept)) {
-      return set(req, DEFAULT);
+      return set(req, Optional.of(DEFAULT));
     }
 
     for (String p : accept.split("[ ,;][ ,;]*")) {
       for (FormatType type : FormatType.values()) {
         if (p.equals(type.mimeType)) {
-          return set(req, type != HTML ? type : DEFAULT);
+          return set(req, Optional.of(type != HTML ? type : DEFAULT));
         }
       }
     }
-    return set(req, DEFAULT);
+    return set(req, Optional.of(DEFAULT));
   }
 
-  private static FormatType set(HttpServletRequest req, FormatType format) {
+  private static Optional<FormatType> set(HttpServletRequest req,
+      Optional<FormatType> format) {
     req.setAttribute(FORMAT_TYPE_ATTRIBUTE, format);
     return format;
   }
diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/HostIndexServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/HostIndexServlet.java
index 79d8927..2cc1351 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/HostIndexServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/HostIndexServlet.java
@@ -15,11 +15,13 @@
 package com.google.gitiles;
 
 import static com.google.common.base.Preconditions.checkNotNull;
+import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;
 import static javax.servlet.http.HttpServletResponse.SC_FORBIDDEN;
 import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
 import static javax.servlet.http.HttpServletResponse.SC_SERVICE_UNAVAILABLE;
 import static javax.servlet.http.HttpServletResponse.SC_UNAUTHORIZED;
 
+import com.google.common.base.Optional;
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Sets;
@@ -104,6 +106,37 @@
   }
 
   @Override
+  protected void doHead(HttpServletRequest req, HttpServletResponse res)
+      throws IOException {
+    Optional<FormatType> format = getFormat(req);
+    if (!format.isPresent()) {
+      res.sendError(SC_BAD_REQUEST);
+      return;
+    }
+
+    GitilesView view = ViewFilter.getView(req);
+    String prefix = view.getRepositoryPrefix();
+    if (prefix != null) {
+      Map<String, RepositoryDescription> descs =
+          list(req, res, prefix, Collections.<String> emptySet());
+      if (descs == null) {
+        return;
+      }
+    }
+    switch (format.get()) {
+      case HTML:
+      case JSON:
+      case TEXT:
+        res.setStatus(HttpServletResponse.SC_OK);
+        res.setContentType(format.get().getMimeType());
+        break;
+      default:
+        res.sendError(SC_BAD_REQUEST);
+        break;
+    }
+  }
+
+  @Override
   protected void doGetHtml(HttpServletRequest req, HttpServletResponse res) throws IOException {
     GitilesView view = ViewFilter.getView(req);
     String prefix = view.getRepositoryPrefix();
diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/RepositoryIndexServlet.java b/gitiles-servlet/src/main/java/com/google/gitiles/RepositoryIndexServlet.java
index 13185fa..d1dfbd8 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/RepositoryIndexServlet.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/RepositoryIndexServlet.java
@@ -15,7 +15,9 @@
 package com.google.gitiles;
 
 import static com.google.common.base.Preconditions.checkNotNull;
+import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;
 
+import com.google.common.base.Optional;
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
@@ -60,6 +62,28 @@
   }
 
   @Override
+  protected void doHead(HttpServletRequest req, HttpServletResponse res)
+      throws IOException {
+    // If the repository didn't exist a prior filter would have 404 replied.
+    Optional<FormatType> format = getFormat(req);
+    if (!format.isPresent()) {
+      res.sendError(SC_BAD_REQUEST);
+      return;
+    }
+    switch (format.get()) {
+      case HTML:
+      case JSON:
+        res.setStatus(HttpServletResponse.SC_OK);
+        res.setContentType(format.get().getMimeType());
+        break;
+      case TEXT:
+        default:
+        res.sendError(SC_BAD_REQUEST);
+        break;
+    }
+  }
+
+  @Override
   protected void doGetHtml(HttpServletRequest req, HttpServletResponse res) throws IOException {
     GitilesView view = ViewFilter.getView(req);
     Repository repo = ServletUtils.getRepository(req);
diff --git a/gitiles-servlet/src/test/java/com/google/gitiles/FakeHttpServletRequest.java b/gitiles-servlet/src/test/java/com/google/gitiles/FakeHttpServletRequest.java
index 5890e78..343b270 100644
--- a/gitiles-servlet/src/test/java/com/google/gitiles/FakeHttpServletRequest.java
+++ b/gitiles-servlet/src/test/java/com/google/gitiles/FakeHttpServletRequest.java
@@ -70,6 +70,7 @@
   private ListMultimap<String, String> parameters;
   private String hostName;
   private int port;
+  private String method;
   private String contextPath;
   private String servletPath;
   private String path;
@@ -79,6 +80,7 @@
     this.hostName = checkNotNull(hostName, "hostName");
     checkArgument(port > 0);
     this.port = port;
+    this.method = "GET";
     this.contextPath = checkNotNull(contextPath, "contextPath");
     this.servletPath = checkNotNull(servletPath, "servletPath");
     attributes = Maps.newConcurrentMap();
@@ -297,7 +299,11 @@
 
   @Override
   public String getMethod() {
-    return "GET";
+    return method;
+  }
+
+  public void setMethod(String m) {
+    method = m;
   }
 
   @Override
diff --git a/gitiles-servlet/src/test/java/com/google/gitiles/HostIndexServletTest.java b/gitiles-servlet/src/test/java/com/google/gitiles/HostIndexServletTest.java
index f96a37c..f98e7bf 100644
--- a/gitiles-servlet/src/test/java/com/google/gitiles/HostIndexServletTest.java
+++ b/gitiles-servlet/src/test/java/com/google/gitiles/HostIndexServletTest.java
@@ -34,6 +34,8 @@
 
 import java.util.Map;
 
+import javax.servlet.http.HttpServletResponse;
+
 /** Tests for {@link HostIndexServlet}. */
 @RunWith(JUnit4.class)
 public class HostIndexServletTest extends ServletTest {
@@ -152,4 +154,34 @@
   public void emptySubdirectoryList() throws Exception {
     assertNotFound("/no.repos/", null);
   }
+
+  @Test
+  public void headOnRoot() throws Exception {
+    FakeHttpServletRequest req = FakeHttpServletRequest.newRequest();
+    req.setMethod("HEAD");
+    req.setPathInfo("/");
+    FakeHttpServletResponse res = new FakeHttpServletResponse();
+    servlet.service(req, res);
+    assertThat(res.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
+  }
+
+  @Test
+  public void headOnMissingSubdir() throws Exception {
+    FakeHttpServletRequest req = FakeHttpServletRequest.newRequest();
+    req.setMethod("HEAD");
+    req.setPathInfo("/no.repos/");
+    FakeHttpServletResponse res = new FakeHttpServletResponse();
+    servlet.service(req, res);
+    assertThat(res.getStatus()).isEqualTo(HttpServletResponse.SC_NOT_FOUND);
+  }
+
+  @Test
+  public void headOnPopulatedSubdir() throws Exception {
+    FakeHttpServletRequest req = FakeHttpServletRequest.newRequest();
+    req.setMethod("HEAD");
+    req.setPathInfo("/foo/");
+    FakeHttpServletResponse res = new FakeHttpServletResponse();
+    servlet.service(req, res);
+    assertThat(res.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
+  }
 }