diff --git a/java/com/google/gitiles/ArchiveServlet.java b/java/com/google/gitiles/ArchiveServlet.java
index 3f03455..ed9fedd 100644
--- a/java/com/google/gitiles/ArchiveServlet.java
+++ b/java/com/google/gitiles/ArchiveServlet.java
@@ -14,10 +14,10 @@
 
 package com.google.gitiles;
 
-import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
 import static javax.servlet.http.HttpServletResponse.SC_OK;
 
 import com.google.common.base.Strings;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import java.io.IOException;
 import java.util.Optional;
 import javax.servlet.ServletException;
@@ -50,15 +50,13 @@
 
     ObjectId treeId = getTree(view, repo, rev);
     if (treeId.equals(ObjectId.zeroId())) {
-      res.sendError(SC_NOT_FOUND);
-      return;
+      throw new GitilesRequestFailureException(FailureReason.INCORRECT_OBJECT_TYPE);
     }
 
     Optional<ArchiveFormat> format =
         ArchiveFormat.byExtension(view.getExtension(), getAccess(req).getConfig());
     if (!format.isPresent()) {
-      res.setStatus(SC_NOT_FOUND);
-      return;
+      throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_RESPONSE_FORMAT);
     }
     String filename = getFilename(view, rev, view.getExtension());
     setDownloadHeaders(req, res, filename, format.get().getMimeType());
diff --git a/java/com/google/gitiles/BaseServlet.java b/java/com/google/gitiles/BaseServlet.java
index 4b8a139..02a3f1a 100644
--- a/java/com/google/gitiles/BaseServlet.java
+++ b/java/com/google/gitiles/BaseServlet.java
@@ -30,6 +30,7 @@
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Maps;
 import com.google.common.net.HttpHeaders;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import com.google.gson.FieldNamingPolicy;
 import com.google.gson.GsonBuilder;
 import java.io.BufferedWriter;
@@ -119,8 +120,7 @@
         break;
       case DEFAULT:
       default:
-        res.sendError(SC_BAD_REQUEST);
-        break;
+        throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_RESPONSE_FORMAT);
     }
   }
 
@@ -147,7 +147,7 @@
    * @param res in-progress response.
    */
   protected void doGetHtml(HttpServletRequest req, HttpServletResponse res) throws IOException {
-    res.sendError(SC_BAD_REQUEST);
+    throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_RESPONSE_FORMAT);
   }
 
   /**
@@ -157,7 +157,7 @@
    * @param res in-progress response.
    */
   protected void doGetText(HttpServletRequest req, HttpServletResponse res) throws IOException {
-    res.sendError(SC_BAD_REQUEST);
+    throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_RESPONSE_FORMAT);
   }
 
   /**
@@ -167,7 +167,7 @@
    * @param res in-progress response.
    */
   protected void doGetJson(HttpServletRequest req, HttpServletResponse res) throws IOException {
-    res.sendError(SC_BAD_REQUEST);
+    throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_RESPONSE_FORMAT);
   }
 
   protected static Map<String, Object> getData(HttpServletRequest req) {
diff --git a/java/com/google/gitiles/DefaultErrorHandlingFilter.java b/java/com/google/gitiles/DefaultErrorHandlingFilter.java
new file mode 100644
index 0000000..958b800
--- /dev/null
+++ b/java/com/google/gitiles/DefaultErrorHandlingFilter.java
@@ -0,0 +1,63 @@
+// Copyright 2019 Google LLC
+//
+// 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
+//
+//     https://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 com.google.gitiles;
+
+import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;
+import static javax.servlet.http.HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
+import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
+import static org.eclipse.jgit.http.server.GitSmartHttpTools.sendError;
+
+import java.io.IOException;
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import org.eclipse.jgit.errors.AmbiguousObjectException;
+import org.eclipse.jgit.errors.RepositoryNotFoundException;
+import org.eclipse.jgit.transport.ServiceMayNotContinueException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/** Convert exceptions into HTTP response. */
+public class DefaultErrorHandlingFilter extends AbstractHttpFilter {
+  private static final Logger log = LoggerFactory.getLogger(DefaultErrorHandlingFilter.class);
+
+  /** HTTP header that indicates an error detail. */
+  public static final String GITILES_ERROR = "X-Gitiles-Error";
+
+  @Override
+  public void doFilter(HttpServletRequest req, HttpServletResponse res, FilterChain chain)
+      throws IOException, ServletException {
+    try {
+      chain.doFilter(req, res);
+    } catch (GitilesRequestFailureException e) {
+      res.setHeader(GITILES_ERROR, e.getReason().toString());
+      String publicMessage = e.getPublicErrorMessage();
+      if (publicMessage != null) {
+        res.sendError(e.getReason().getHttpStatusCode(), publicMessage);
+      } else {
+        res.sendError(e.getReason().getHttpStatusCode());
+      }
+    } catch (RepositoryNotFoundException e) {
+      res.sendError(SC_NOT_FOUND);
+    } catch (AmbiguousObjectException e) {
+      res.sendError(SC_BAD_REQUEST);
+    } catch (ServiceMayNotContinueException e) {
+      sendError(req, res, e.getStatusCode(), e.getMessage());
+    } catch (IOException | ServletException err) {
+      log.warn("Internal server error", err);
+      res.sendError(SC_INTERNAL_SERVER_ERROR);
+    }
+  }
+}
diff --git a/java/com/google/gitiles/DescribeServlet.java b/java/com/google/gitiles/DescribeServlet.java
index 785d452..ebd2ea4 100644
--- a/java/com/google/gitiles/DescribeServlet.java
+++ b/java/com/google/gitiles/DescribeServlet.java
@@ -14,11 +14,9 @@
 
 package com.google.gitiles;
 
-import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;
-import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
-
 import com.google.common.base.Joiner;
 import com.google.common.collect.ImmutableMap;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import com.google.gson.reflect.TypeToken;
 import java.io.IOException;
 import java.io.Writer;
@@ -84,21 +82,14 @@
     try {
       return repo.resolve(rev);
     } catch (RevisionSyntaxException e) {
-      renderTextError(
-          req,
-          res,
-          SC_BAD_REQUEST,
-          "Invalid revision syntax: " + RefServlet.sanitizeRefForText(rev));
-      return null;
+      throw new GitilesRequestFailureException(FailureReason.INCORECT_PARAMETER)
+          .withPublicErrorMessage(
+              "Invalid revision syntax: %s", RefServlet.sanitizeRefForText(rev));
     } catch (AmbiguousObjectException e) {
-      renderTextError(
-          req,
-          res,
-          SC_BAD_REQUEST,
-          String.format(
+      throw new GitilesRequestFailureException(FailureReason.AMBIGUOUS_OBJECT)
+          .withPublicErrorMessage(
               "Ambiguous short SHA-1 %s (%s)",
-              e.getAbbreviatedObjectId(), Joiner.on(", ").join(e.getCandidates())));
-      return null;
+              e.getAbbreviatedObjectId(), Joiner.on(", ").join(e.getCandidates()));
     }
   }
 
@@ -106,8 +97,7 @@
       Repository repo, GitilesView view, HttpServletRequest req, HttpServletResponse res)
       throws IOException {
     if (!getBooleanParam(view, CONTAINS_PARAM)) {
-      res.setStatus(SC_BAD_REQUEST);
-      return null;
+      throw new GitilesRequestFailureException(FailureReason.INCORECT_PARAMETER);
     }
     ObjectId id = resolve(repo, view, req, res);
     if (id == null) {
@@ -124,8 +114,7 @@
       throw new IOException(e);
     }
     if (name == null) {
-      res.setStatus(SC_NOT_FOUND);
-      return null;
+      throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
     }
     return name;
   }
@@ -137,8 +126,8 @@
     boolean all = getBooleanParam(view, ALL_PARAM);
     boolean tags = getBooleanParam(view, TAGS_PARAM);
     if (all && tags) {
-      renderTextError(req, res, SC_BAD_REQUEST, "Cannot specify both \"all\" and \"tags\"");
-      return null;
+      throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_REVISION_NAMES)
+          .withPublicErrorMessage("Cannot specify both \"all\" and \"tags\"");
     }
     if (all) {
       cmd.addPrefix(Constants.R_REFS);
diff --git a/java/com/google/gitiles/DiffServlet.java b/java/com/google/gitiles/DiffServlet.java
index d0e4409..5b1801d 100644
--- a/java/com/google/gitiles/DiffServlet.java
+++ b/java/com/google/gitiles/DiffServlet.java
@@ -15,11 +15,11 @@
 package com.google.gitiles;
 
 import static com.google.common.base.Preconditions.checkNotNull;
-import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
 
 import com.google.common.io.BaseEncoding;
 import com.google.gitiles.CommitData.Field;
 import com.google.gitiles.DateFormatter.Format;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.io.Writer;
@@ -67,8 +67,7 @@
       AbstractTreeIterator newTree;
       try {
         if (tw == null && !view.getPathPart().isEmpty()) {
-          res.setStatus(SC_NOT_FOUND);
-          return;
+          throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
         }
         isFile = tw != null && isFile(tw);
 
@@ -77,9 +76,10 @@
         showCommit = isParentOf(walk, view.getOldRevision(), view.getRevision());
         oldTree = getTreeIterator(walk, view.getOldRevision().getId());
         newTree = getTreeIterator(walk, view.getRevision().getId());
-      } catch (MissingObjectException | IncorrectObjectTypeException e) {
-        res.setStatus(SC_NOT_FOUND);
-        return;
+      } catch (MissingObjectException e) {
+        throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND, e);
+      } catch (IncorrectObjectTypeException e) {
+        throw new GitilesRequestFailureException(FailureReason.INCORRECT_OBJECT_TYPE, e);
       }
 
       Map<String, Object> data = getData(req);
@@ -124,9 +124,10 @@
       try {
         oldTree = getTreeIterator(walk, view.getOldRevision().getId());
         newTree = getTreeIterator(walk, view.getRevision().getId());
-      } catch (MissingObjectException | IncorrectObjectTypeException e) {
-        res.setStatus(SC_NOT_FOUND);
-        return;
+      } catch (MissingObjectException e) {
+        throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND, e);
+      } catch (IncorrectObjectTypeException e) {
+        throw new GitilesRequestFailureException(FailureReason.INCORRECT_OBJECT_TYPE, e);
       }
 
       try (Writer writer = startRenderText(req, res);
diff --git a/java/com/google/gitiles/GitilesFilter.java b/java/com/google/gitiles/GitilesFilter.java
index 59e8acd..2c810bb 100644
--- a/java/com/google/gitiles/GitilesFilter.java
+++ b/java/com/google/gitiles/GitilesFilter.java
@@ -37,6 +37,7 @@
 import java.util.Iterator;
 import java.util.Map;
 import java.util.regex.Pattern;
+import javax.annotation.Nullable;
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
@@ -174,20 +175,22 @@
   private TimeCache timeCache;
   private BlameCache blameCache;
   private GitwebRedirectFilter gitwebRedirect;
+  private Filter errorHandler;
   private boolean initialized;
 
   GitilesFilter() {}
 
   GitilesFilter(
       Config config,
-      Renderer renderer,
-      GitilesUrls urls,
-      GitilesAccess.Factory accessFactory,
-      final RepositoryResolver<HttpServletRequest> resolver,
-      VisibilityCache visibilityCache,
-      TimeCache timeCache,
-      BlameCache blameCache,
-      GitwebRedirectFilter gitwebRedirect) {
+      @Nullable Renderer renderer,
+      @Nullable GitilesUrls urls,
+      @Nullable GitilesAccess.Factory accessFactory,
+      @Nullable RepositoryResolver<HttpServletRequest> resolver,
+      @Nullable VisibilityCache visibilityCache,
+      @Nullable TimeCache timeCache,
+      @Nullable BlameCache blameCache,
+      @Nullable GitwebRedirectFilter gitwebRedirect,
+      @Nullable Filter errorHandler) {
     this.config = checkNotNull(config, "config");
     this.renderer = renderer;
     this.urls = urls;
@@ -199,6 +202,7 @@
     if (resolver != null) {
       this.resolver = resolver;
     }
+    this.errorHandler = errorHandler;
   }
 
   @Override
@@ -232,6 +236,12 @@
     initialized = true;
   }
 
+  @Override
+  protected ServletBinder register(ServletBinder b) {
+    b.through(errorHandler);
+    return b;
+  }
+
   public synchronized BaseServlet getDefaultHandler(GitilesView.Type view) {
     checkNotInitialized();
     switch (view) {
@@ -300,6 +310,7 @@
     setDefaultTimeCache();
     setDefaultBlameCache();
     setDefaultGitwebRedirect();
+    setDefaultErrorHandler();
   }
 
   private void setDefaultConfig(FilterConfig filterConfig) throws ServletException {
@@ -407,6 +418,12 @@
     }
   }
 
+  private void setDefaultErrorHandler() {
+    if (errorHandler == null) {
+      errorHandler = new DefaultErrorHandlingFilter();
+    }
+  }
+
   private static String getBaseGitUrl(Config config) throws ServletException {
     String baseGitUrl = config.getString("gitiles", null, "baseGitUrl");
     if (baseGitUrl == null) {
diff --git a/java/com/google/gitiles/GitilesRequestFailureException.java b/java/com/google/gitiles/GitilesRequestFailureException.java
new file mode 100644
index 0000000..91f9cf8
--- /dev/null
+++ b/java/com/google/gitiles/GitilesRequestFailureException.java
@@ -0,0 +1,163 @@
+// Copyright 2019 Google LLC
+//
+// 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
+//
+//     https://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 com.google.gitiles;
+
+import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;
+import static javax.servlet.http.HttpServletResponse.SC_FORBIDDEN;
+import static javax.servlet.http.HttpServletResponse.SC_GONE;
+import static javax.servlet.http.HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
+import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
+import static javax.servlet.http.HttpServletResponse.SC_UNAUTHORIZED;
+
+import javax.annotation.Nullable;
+
+/**
+ * Indicates the request should be failed.
+ *
+ * <p>When an HTTP request should be failed, throw this exception instead of directly setting an
+ * HTTP status code. The exception is caught by an error handler in {@link GitilesFilter}. By
+ * default, {@link DefaultErrorHandlingFilter} handles this exception and set an appropriate HTTP
+ * status code. If you want to customize how the error is surfaced, like changing the error page
+ * rendering, replace this error handler from {@link GitilesServlet}.
+ *
+ * <h2>Extending the error space</h2>
+ *
+ * <p>{@link GitilesServlet} lets you customize some parts of Gitiles, and sometimes you would like
+ * to create a new {@link FailureReason}. For example, a customized {@code RepositoryResolver} might
+ * check a request quota and reject a request if a client sends too many requests. In that case, you
+ * can define your own {@link RuntimeException} and an error handler.
+ *
+ * <pre><code>
+ *   public final class MyRequestFailureException extends RuntimeException {
+ *     private final FailureReason reason;
+ *
+ *     public MyRequestFailureException(FailureReason reason) {
+ *       super();
+ *       this.reason = reason;
+ *     }
+ *
+ *     public FailureReason getReason() {
+ *       return reason;
+ *     }
+ *
+ *     enum FailureReason {
+ *       QUOTA_EXCEEDED(429);
+ *     }
+ *
+ *     private final int httpStatusCode;
+ *
+ *     FailureReason(int httpStatusCode) {
+ *       this.httpStatusCode = httpStatusCode;
+ *     }
+ *
+ *     public int getHttpStatusCode() {
+ *       return httpStatusCode;
+ *     }
+ *   }
+ *
+ *   public class MyErrorHandlingFilter extends AbstractHttpFilter {
+ *     private static final DefaultErrorHandlingFilter delegate =
+ *         new DefaultErrorHandlingFilter();
+ *
+ *     {@literal @}Override
+ *     public void doFilter(HttpServletRequest req, HttpServletResponse res, FilterChain chain)
+ *         throws IOException, ServletException {
+ *       try {
+ *         delegate.doFilter(req, res, chain);
+ *       } catch (MyRequestFailureException e) {
+ *         res.setHeader(DefaultErrorHandlingFilter.GITILES_ERROR, e.getReason().toString());
+ *         res.sendError(e.getReason().getHttpStatusCode());
+ *       }
+ *     }
+ *   }
+ * </code></pre>
+ *
+ * <p>{@code RepositoryResolver} can throw {@code MyRequestFailureException} and {@code
+ * MyErrorHandlingFilter} will handle that. You can control how the error should be surfaced.
+ */
+public final class GitilesRequestFailureException extends RuntimeException {
+  private final FailureReason reason;
+  private String publicErrorMessage;
+
+  public GitilesRequestFailureException(FailureReason reason) {
+    super();
+    this.reason = reason;
+  }
+
+  public GitilesRequestFailureException(FailureReason reason, Throwable cause) {
+    super(cause);
+    this.reason = reason;
+  }
+
+  public GitilesRequestFailureException withPublicErrorMessage(String format, Object... params) {
+    this.publicErrorMessage = String.format(format, params);
+    return this;
+  }
+
+  public FailureReason getReason() {
+    return reason;
+  }
+
+  @Nullable
+  public String getPublicErrorMessage() {
+    return publicErrorMessage;
+  }
+
+  /** The request failure reason. */
+  public enum FailureReason {
+    /** The object specified by the URL is ambiguous and Gitiles cannot identify one object. */
+    AMBIGUOUS_OBJECT(SC_BAD_REQUEST),
+    /** There's nothing to show for blame (e.g. the file is empty). */
+    BLAME_REGION_NOT_FOUND(SC_NOT_FOUND),
+    /** Cannot parse URL as a Gitiles URL. */
+    CANNOT_PARSE_GITILES_VIEW(SC_NOT_FOUND),
+    /** URL parameters are not valid. */
+    INCORECT_PARAMETER(SC_BAD_REQUEST),
+    /**
+     * The object specified by the URL is not suitable for the view (e.g. trying to show a blob as a
+     * tree).
+     */
+    INCORRECT_OBJECT_TYPE(SC_BAD_REQUEST),
+    /** Markdown rendering is not enabled. */
+    MARKDOWN_NOT_ENABLED(SC_NOT_FOUND),
+    /** Request is not authorized. */
+    NOT_AUTHORIZED(SC_UNAUTHORIZED),
+    /** Object is not found. */
+    OBJECT_NOT_FOUND(SC_NOT_FOUND),
+    /** Object is too large to show. */
+    OBJECT_TOO_LARGE(SC_INTERNAL_SERVER_ERROR),
+    /** Repository is not found. */
+    REPOSITORY_NOT_FOUND(SC_NOT_FOUND),
+    /** Gitiles is not enabled for the repository. */
+    SERVICE_NOT_ENABLED(SC_FORBIDDEN),
+    /** GitWeb URL cannot be converted to Gitiles URL. */
+    UNSUPPORTED_GITWEB_URL(SC_GONE),
+    /** The specified object's type is not supported. */
+    UNSUPPORTED_OBJECT_TYPE(SC_NOT_FOUND),
+    /** The specified format type is not supported. */
+    UNSUPPORTED_RESPONSE_FORMAT(SC_BAD_REQUEST),
+    /** The specified revision names are not supported. */
+    UNSUPPORTED_REVISION_NAMES(SC_BAD_REQUEST);
+
+    private final int httpStatusCode;
+
+    FailureReason(int httpStatusCode) {
+      this.httpStatusCode = httpStatusCode;
+    }
+
+    public int getHttpStatusCode() {
+      return httpStatusCode;
+    }
+  }
+}
diff --git a/java/com/google/gitiles/GitilesServlet.java b/java/com/google/gitiles/GitilesServlet.java
index 56f4c61..6d10c0c 100644
--- a/java/com/google/gitiles/GitilesServlet.java
+++ b/java/com/google/gitiles/GitilesServlet.java
@@ -52,6 +52,30 @@
       @Nullable TimeCache timeCache,
       @Nullable BlameCache blameCache,
       @Nullable GitwebRedirectFilter gitwebRedirect) {
+    this(
+        config,
+        renderer,
+        urls,
+        accessFactory,
+        resolver,
+        visibilityCache,
+        timeCache,
+        blameCache,
+        gitwebRedirect,
+        null);
+  }
+
+  public GitilesServlet(
+      Config config,
+      @Nullable Renderer renderer,
+      @Nullable GitilesUrls urls,
+      @Nullable GitilesAccess.Factory accessFactory,
+      @Nullable RepositoryResolver<HttpServletRequest> resolver,
+      @Nullable VisibilityCache visibilityCache,
+      @Nullable TimeCache timeCache,
+      @Nullable BlameCache blameCache,
+      @Nullable GitwebRedirectFilter gitwebRedirect,
+      @Nullable Filter errorHandler) {
     super(
         new GitilesFilter(
             config,
@@ -62,7 +86,8 @@
             visibilityCache,
             timeCache,
             blameCache,
-            gitwebRedirect));
+            gitwebRedirect,
+            errorHandler));
   }
 
   public GitilesServlet() {
diff --git a/java/com/google/gitiles/GitwebRedirectFilter.java b/java/com/google/gitiles/GitwebRedirectFilter.java
index f1e01bc..324af72 100644
--- a/java/com/google/gitiles/GitwebRedirectFilter.java
+++ b/java/com/google/gitiles/GitwebRedirectFilter.java
@@ -18,7 +18,6 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.net.HttpHeaders.LOCATION;
 import static java.nio.charset.StandardCharsets.UTF_8;
-import static javax.servlet.http.HttpServletResponse.SC_GONE;
 import static javax.servlet.http.HttpServletResponse.SC_MOVED_PERMANENTLY;
 
 import com.google.common.base.Splitter;
@@ -27,6 +26,7 @@
 import com.google.common.collect.LinkedListMultimap;
 import com.google.common.collect.ListMultimap;
 import com.google.gitiles.GitilesView.InvalidViewException;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 import java.net.URLDecoder;
@@ -117,8 +117,7 @@
     } else {
       // Gitiles does not provide an RSS feed (a=rss,atom,opml)
       // Any other URL is out of date and not valid anymore.
-      res.sendError(SC_GONE);
-      return;
+      throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_GITWEB_URL);
     }
 
     if (!Strings.isNullOrEmpty(project)) {
@@ -132,8 +131,7 @@
               .setServletPath(gitwebView.getServletPath())
               .toUrl();
     } catch (InvalidViewException e) {
-      res.setStatus(SC_GONE);
-      return;
+      throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_GITWEB_URL);
     }
     res.setStatus(SC_MOVED_PERMANENTLY);
     res.setHeader(LOCATION, url);
diff --git a/java/com/google/gitiles/HostIndexServlet.java b/java/com/google/gitiles/HostIndexServlet.java
index d23aa3c..ce2ec6b 100644
--- a/java/com/google/gitiles/HostIndexServlet.java
+++ b/java/com/google/gitiles/HostIndexServlet.java
@@ -15,16 +15,11 @@
 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 static org.eclipse.jgit.http.server.GitSmartHttpTools.sendError;
 
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Sets;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import com.google.gson.reflect.TypeToken;
 import com.google.template.soy.data.SoyListData;
 import com.google.template.soy.data.SoyMapData;
@@ -40,8 +35,6 @@
 import javax.annotation.Nullable;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
-import org.eclipse.jgit.errors.RepositoryNotFoundException;
-import org.eclipse.jgit.transport.ServiceMayNotContinueException;
 import org.eclipse.jgit.transport.resolver.ServiceNotAuthorizedException;
 import org.eclipse.jgit.transport.resolver.ServiceNotEnabledException;
 import org.slf4j.Logger;
@@ -66,27 +59,13 @@
     Map<String, RepositoryDescription> descs;
     try {
       descs = getAccess(req).listRepositories(prefix, branches);
-    } catch (RepositoryNotFoundException e) {
-      res.sendError(SC_NOT_FOUND);
-      return null;
     } catch (ServiceNotEnabledException e) {
-      res.sendError(SC_FORBIDDEN);
-      return null;
+      throw new GitilesRequestFailureException(FailureReason.SERVICE_NOT_ENABLED, e);
     } catch (ServiceNotAuthorizedException e) {
-      res.sendError(SC_UNAUTHORIZED);
-      return null;
-    } catch (ServiceMayNotContinueException e) {
-      sendError(req, res, e.getStatusCode(), e.getMessage());
-      return null;
-    } catch (IOException err) {
-      String name = urls.getHostName(req);
-      log.warn("Cannot scan repositories" + (name != null ? " for " + name : ""), err);
-      res.sendError(SC_SERVICE_UNAVAILABLE);
-      return null;
+      throw new GitilesRequestFailureException(FailureReason.NOT_AUTHORIZED, e);
     }
     if (prefix != null && descs.isEmpty()) {
-      res.sendError(SC_NOT_FOUND);
-      return null;
+      throw new GitilesRequestFailureException(FailureReason.REPOSITORY_NOT_FOUND);
     }
     return descs;
   }
@@ -103,15 +82,14 @@
   protected void doHead(HttpServletRequest req, HttpServletResponse res) throws IOException {
     Optional<FormatType> format = getFormat(req);
     if (!format.isPresent()) {
-      res.sendError(SC_BAD_REQUEST);
-      return;
+      throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_RESPONSE_FORMAT);
     }
 
     GitilesView view = ViewFilter.getView(req);
     String prefix = view.getRepositoryPrefix();
     if (prefix != null) {
       Map<String, RepositoryDescription> descs =
-          list(req, res, prefix, Collections.<String>emptySet());
+          list(req, res, prefix, Collections.emptySet());
       if (descs == null) {
         return;
       }
@@ -125,8 +103,7 @@
         break;
       case DEFAULT:
       default:
-        res.sendError(SC_BAD_REQUEST);
-        break;
+        throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_RESPONSE_FORMAT);
     }
   }
 
diff --git a/java/com/google/gitiles/LogServlet.java b/java/com/google/gitiles/LogServlet.java
index f1bdd95..3523846 100644
--- a/java/com/google/gitiles/LogServlet.java
+++ b/java/com/google/gitiles/LogServlet.java
@@ -15,8 +15,6 @@
 package com.google.gitiles;
 
 import static com.google.common.base.Preconditions.checkNotNull;
-import static javax.servlet.http.HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
-import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
 
 import com.google.common.base.Strings;
 import com.google.common.collect.Iterables;
@@ -27,6 +25,7 @@
 import com.google.common.primitives.Longs;
 import com.google.gitiles.CommitData.Field;
 import com.google.gitiles.DateFormatter.Format;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import com.google.gson.reflect.TypeToken;
 import java.io.IOException;
 import java.io.OutputStream;
@@ -42,7 +41,6 @@
 import org.eclipse.jgit.diff.DiffConfig;
 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
-import org.eclipse.jgit.errors.RevWalkException;
 import org.eclipse.jgit.http.server.ServletUtils;
 import org.eclipse.jgit.lib.AbbreviatedObjectId;
 import org.eclipse.jgit.lib.Constants;
@@ -97,8 +95,7 @@
       GitilesAccess access = getAccess(req);
       paginator = newPaginator(repo, view, access);
       if (paginator == null) {
-        res.setStatus(SC_NOT_FOUND);
-        return;
+        throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
       }
       DateFormatter df = new DateFormatter(access, Format.DEFAULT);
 
@@ -133,10 +130,6 @@
             .renderStreaming(paginator, null, renderer, w, df, LogSoyData.FooterBehavior.NEXT);
         w.flush();
       }
-    } catch (RevWalkException e) {
-      log.warn("Error in rev walk", e);
-      res.setStatus(SC_INTERNAL_SERVER_ERROR);
-      return;
     } finally {
       if (paginator != null) {
         paginator.getWalk().close();
@@ -160,8 +153,7 @@
       GitilesAccess access = getAccess(req);
       paginator = newPaginator(repo, view, access);
       if (paginator == null) {
-        res.setStatus(SC_NOT_FOUND);
-        return;
+        throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
       }
       DateFormatter df = new DateFormatter(access, Format.DEFAULT);
       CommitJsonData.Log result = new CommitJsonData.Log();
diff --git a/java/com/google/gitiles/PathServlet.java b/java/com/google/gitiles/PathServlet.java
index 0ecb875..dac38d3 100644
--- a/java/com/google/gitiles/PathServlet.java
+++ b/java/com/google/gitiles/PathServlet.java
@@ -16,8 +16,6 @@
 
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.gitiles.TreeSoyData.resolveTargetUrl;
-import static javax.servlet.http.HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
-import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
 import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
 import static org.eclipse.jgit.lib.Constants.OBJ_COMMIT;
 import static org.eclipse.jgit.lib.Constants.OBJ_TREE;
@@ -29,6 +27,7 @@
 import com.google.common.collect.Maps;
 import com.google.common.io.BaseEncoding;
 import com.google.common.primitives.Bytes;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.io.Writer;
@@ -131,8 +130,7 @@
     try (RevWalk rw = new RevWalk(repo);
         WalkResult wr = WalkResult.forPath(rw, view, false)) {
       if (wr == null) {
-        res.setStatus(SC_NOT_FOUND);
-        return;
+        throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
       }
       switch (wr.type) {
         case TREE:
@@ -149,12 +147,10 @@
           showGitlink(req, res, wr);
           break;
         default:
-          log.error("Bad file type: {}", wr.type);
-          res.setStatus(SC_NOT_FOUND);
-          break;
+          throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_OBJECT_TYPE);
       }
     } catch (LargeObjectException e) {
-      res.setStatus(SC_INTERNAL_SERVER_ERROR);
+      throw new GitilesRequestFailureException(FailureReason.OBJECT_TOO_LARGE, e);
     }
   }
 
@@ -166,8 +162,7 @@
     try (RevWalk rw = new RevWalk(repo);
         WalkResult wr = WalkResult.forPath(rw, view, false)) {
       if (wr == null) {
-        res.setStatus(SC_NOT_FOUND);
-        return;
+        throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
       }
 
       // Write base64 as plain text without modifying any other headers, under
@@ -185,11 +180,10 @@
           break;
         case GITLINK:
         default:
-          renderTextError(req, res, SC_NOT_FOUND, "Not a file");
-          break;
+          throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_OBJECT_TYPE);
       }
     } catch (LargeObjectException e) {
-      res.setStatus(SC_INTERNAL_SERVER_ERROR);
+      throw new GitilesRequestFailureException(FailureReason.OBJECT_TOO_LARGE, e);
     }
   }
 
@@ -252,8 +246,7 @@
     try (RevWalk rw = new RevWalk(repo);
         WalkResult wr = WalkResult.forPath(rw, view, recursive)) {
       if (wr == null) {
-        res.setStatus(SC_NOT_FOUND);
-        return;
+        throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
       }
       switch (wr.type) {
         case REGULAR_FILE:
@@ -275,11 +268,10 @@
         case GITLINK:
         case SYMLINK:
         default:
-          res.setStatus(SC_NOT_FOUND);
-          break;
+          throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_OBJECT_TYPE);
       }
     } catch (LargeObjectException e) {
-      res.setStatus(SC_INTERNAL_SERVER_ERROR);
+      throw new GitilesRequestFailureException(FailureReason.OBJECT_TOO_LARGE, e);
     }
   }
 
diff --git a/java/com/google/gitiles/RefServlet.java b/java/com/google/gitiles/RefServlet.java
index 2b16ef5..fd93126 100644
--- a/java/com/google/gitiles/RefServlet.java
+++ b/java/com/google/gitiles/RefServlet.java
@@ -16,7 +16,6 @@
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
-import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
@@ -25,6 +24,7 @@
 import com.google.common.collect.Ordering;
 import com.google.common.primitives.Ints;
 import com.google.common.util.concurrent.UncheckedExecutionException;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import com.google.gson.reflect.TypeToken;
 import java.io.IOException;
 import java.io.Writer;
@@ -59,8 +59,7 @@
   @Override
   protected void doGetHtml(HttpServletRequest req, HttpServletResponse res) throws IOException {
     if (!ViewFilter.getView(req).getPathPart().isEmpty()) {
-      res.setStatus(SC_NOT_FOUND);
-      return;
+      throw new GitilesRequestFailureException(FailureReason.INCORECT_PARAMETER);
     }
     List<Map<String, Object>> tags;
     try (RevWalk walk = new RevWalk(ServletUtils.getRepository(req))) {
diff --git a/java/com/google/gitiles/RepositoryFilter.java b/java/com/google/gitiles/RepositoryFilter.java
index fa9d601..a25a8de 100644
--- a/java/com/google/gitiles/RepositoryFilter.java
+++ b/java/com/google/gitiles/RepositoryFilter.java
@@ -16,11 +16,9 @@
 
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.gitiles.ViewFilter.getRegexGroup;
-import static javax.servlet.http.HttpServletResponse.SC_FORBIDDEN;
-import static javax.servlet.http.HttpServletResponse.SC_UNAUTHORIZED;
-import static org.eclipse.jgit.http.server.GitSmartHttpTools.sendError;
 import static org.eclipse.jgit.http.server.ServletUtils.ATTRIBUTE_REPOSITORY;
 
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import java.io.IOException;
 import javax.servlet.FilterChain;
 import javax.servlet.ServletException;
@@ -28,12 +26,12 @@
 import javax.servlet.http.HttpServletResponse;
 import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.Repository;
-import org.eclipse.jgit.transport.ServiceMayNotContinueException;
 import org.eclipse.jgit.transport.resolver.RepositoryResolver;
 import org.eclipse.jgit.transport.resolver.ServiceNotAuthorizedException;
 import org.eclipse.jgit.transport.resolver.ServiceNotEnabledException;
 
 class RepositoryFilter extends AbstractHttpFilter {
+
   private final RepositoryResolver<HttpServletRequest> resolver;
 
   RepositoryFilter(RepositoryResolver<HttpServletRequest> resolver) {
@@ -53,15 +51,13 @@
         // to HostIndexServlet which will attempt to list repositories
         // or send SC_NOT_FOUND there.
         chain.doFilter(req, res);
-      } catch (ServiceMayNotContinueException e) {
-        sendError(req, res, e.getStatusCode(), e.getMessage());
       } finally {
         req.removeAttribute(ATTRIBUTE_REPOSITORY);
       }
     } catch (ServiceNotEnabledException e) {
-      sendError(req, res, SC_FORBIDDEN);
+      throw new GitilesRequestFailureException(FailureReason.SERVICE_NOT_ENABLED, e);
     } catch (ServiceNotAuthorizedException e) {
-      res.sendError(SC_UNAUTHORIZED);
+      throw new GitilesRequestFailureException(FailureReason.NOT_AUTHORIZED, e);
     }
   }
 }
diff --git a/java/com/google/gitiles/RepositoryIndexServlet.java b/java/com/google/gitiles/RepositoryIndexServlet.java
index 8e13155..d057512 100644
--- a/java/com/google/gitiles/RepositoryIndexServlet.java
+++ b/java/com/google/gitiles/RepositoryIndexServlet.java
@@ -15,7 +15,6 @@
 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.Strings;
 import com.google.common.collect.ImmutableList;
@@ -23,6 +22,7 @@
 import com.google.common.collect.Maps;
 import com.google.common.html.types.SafeHtml;
 import com.google.gitiles.DateFormatter.Format;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import com.google.gitiles.doc.MarkdownConfig;
 import com.google.gson.reflect.TypeToken;
 import java.io.IOException;
@@ -65,8 +65,7 @@
     // 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;
+      throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_RESPONSE_FORMAT);
     }
     switch (format.get()) {
       case HTML:
@@ -77,8 +76,7 @@
       case TEXT:
       case DEFAULT:
       default:
-        res.sendError(SC_BAD_REQUEST);
-        break;
+        throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_RESPONSE_FORMAT);
     }
   }
 
diff --git a/java/com/google/gitiles/RevisionServlet.java b/java/com/google/gitiles/RevisionServlet.java
index 597c053..8bf661f 100644
--- a/java/com/google/gitiles/RevisionServlet.java
+++ b/java/com/google/gitiles/RevisionServlet.java
@@ -15,7 +15,6 @@
 package com.google.gitiles;
 
 import static com.google.common.base.Preconditions.checkNotNull;
-import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
 import static org.eclipse.jgit.lib.Constants.OBJ_BLOB;
 import static org.eclipse.jgit.lib.Constants.OBJ_COMMIT;
 import static org.eclipse.jgit.lib.Constants.OBJ_TAG;
@@ -28,6 +27,7 @@
 import com.google.gitiles.CommitData.Field;
 import com.google.gitiles.CommitJsonData.Commit;
 import com.google.gitiles.DateFormatter.Format;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.io.Writer;
@@ -125,18 +125,12 @@
                       new TagSoyData(linkifier, req).toSoyData(walk, (RevTag) obj, df)));
               break;
             default:
-              log.warn("Bad object type for {}: {}", ObjectId.toString(obj.getId()), obj.getType());
-              res.setStatus(SC_NOT_FOUND);
-              return;
+              throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_OBJECT_TYPE);
           }
         } catch (MissingObjectException e) {
-          log.warn("Missing object " + ObjectId.toString(obj.getId()), e);
-          res.setStatus(SC_NOT_FOUND);
-          return;
+          throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND, e);
         } catch (IncorrectObjectTypeException e) {
-          log.warn("Incorrect object type for " + ObjectId.toString(obj.getId()), e);
-          res.setStatus(SC_NOT_FOUND);
-          return;
+          throw new GitilesRequestFailureException(FailureReason.INCORRECT_OBJECT_TYPE, e);
         }
       }
 
@@ -159,7 +153,7 @@
     try (ObjectReader reader = repo.newObjectReader()) {
       ObjectLoader loader = reader.open(view.getRevision().getId());
       if (loader.getType() != OBJ_COMMIT) {
-        res.setStatus(SC_NOT_FOUND);
+        throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_OBJECT_TYPE);
       } else {
         PathServlet.setTypeHeader(res, loader.getType());
         try (Writer writer = startRenderText(req, res);
@@ -188,8 +182,7 @@
           break;
         default:
           // TODO(dborowitz): Support showing other types.
-          res.setStatus(SC_NOT_FOUND);
-          break;
+          throw new GitilesRequestFailureException(FailureReason.UNSUPPORTED_OBJECT_TYPE);
       }
     }
   }
diff --git a/java/com/google/gitiles/RootedDocServlet.java b/java/com/google/gitiles/RootedDocServlet.java
index 96329b1..bf72b32 100644
--- a/java/com/google/gitiles/RootedDocServlet.java
+++ b/java/com/google/gitiles/RootedDocServlet.java
@@ -16,6 +16,7 @@
 
 import static org.eclipse.jgit.http.server.ServletUtils.ATTRIBUTE_REPOSITORY;
 
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import com.google.gitiles.doc.DocServlet;
 import com.google.gitiles.doc.HtmlSanitizer;
 import java.io.IOException;
@@ -24,7 +25,6 @@
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
-import org.eclipse.jgit.errors.RepositoryNotFoundException;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevCommit;
@@ -74,14 +74,12 @@
         RevWalk rw = new RevWalk(repo)) {
       ObjectId id = repo.resolve(BRANCH);
       if (id == null) {
-        res.sendError(HttpServletResponse.SC_NOT_FOUND);
-        return;
+        throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
       }
 
       RevObject obj = rw.peel(rw.parseAny(id));
       if (!(obj instanceof RevCommit)) {
-        res.sendError(HttpServletResponse.SC_NOT_FOUND);
-        return;
+        throw new GitilesRequestFailureException(FailureReason.INCORRECT_OBJECT_TYPE);
       }
 
       req.setAttribute(ATTRIBUTE_REPOSITORY, repo);
@@ -95,11 +93,10 @@
               .build());
 
       docServlet.service(req, res);
-    } catch (RepositoryNotFoundException
-        | ServiceNotAuthorizedException
-        | ServiceNotEnabledException e) {
-      log.error(String.format("cannot open repository for %s", req.getServerName()), e);
-      res.sendError(HttpServletResponse.SC_NOT_FOUND);
+    } catch (ServiceNotAuthorizedException e) {
+      throw new GitilesRequestFailureException(FailureReason.NOT_AUTHORIZED, e);
+    } catch (ServiceNotEnabledException e) {
+      throw new GitilesRequestFailureException(FailureReason.SERVICE_NOT_ENABLED, e);
     } finally {
       ViewFilter.removeView(req);
       req.removeAttribute(ATTRIBUTE_REPOSITORY);
diff --git a/java/com/google/gitiles/ViewFilter.java b/java/com/google/gitiles/ViewFilter.java
index 03e8d9a..590e583 100644
--- a/java/com/google/gitiles/ViewFilter.java
+++ b/java/com/google/gitiles/ViewFilter.java
@@ -16,12 +16,10 @@
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
-import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
-import static javax.servlet.http.HttpServletResponse.SC_SERVICE_UNAVAILABLE;
-import static org.eclipse.jgit.http.server.GitSmartHttpTools.sendError;
 import static org.eclipse.jgit.http.server.ServletUtils.ATTRIBUTE_REPOSITORY;
 
 import com.google.common.base.Strings;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import java.io.IOException;
 import java.util.Map;
 import javax.servlet.FilterChain;
@@ -30,7 +28,6 @@
 import javax.servlet.http.HttpServletResponse;
 import org.eclipse.jgit.http.server.ServletUtils;
 import org.eclipse.jgit.http.server.glue.WrappedRequest;
-import org.eclipse.jgit.transport.ServiceMayNotContinueException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -102,21 +99,9 @@
   @Override
   public void doFilter(HttpServletRequest req, HttpServletResponse res, FilterChain chain)
       throws IOException, ServletException {
-    GitilesView.Builder view;
-    try {
-      view = parse(req);
-    } catch (ServiceMayNotContinueException e) {
-      sendError(req, res, e.getStatusCode(), e.getMessage());
-      return;
-    } catch (IOException err) {
-      String name = urls.getHostName(req);
-      log.warn("Cannot parse view" + (name != null ? " for " + name : ""), err);
-      res.setStatus(SC_SERVICE_UNAVAILABLE);
-      return;
-    }
+    GitilesView.Builder view = parse(req);
     if (view == null) {
-      res.setStatus(SC_NOT_FOUND);
-      return;
+      throw new GitilesRequestFailureException(FailureReason.CANNOT_PARSE_GITILES_VIEW);
     }
 
     @SuppressWarnings("unchecked")
diff --git a/java/com/google/gitiles/blame/BlameServlet.java b/java/com/google/gitiles/blame/BlameServlet.java
index 605ac6f..f1b9976 100644
--- a/java/com/google/gitiles/blame/BlameServlet.java
+++ b/java/com/google/gitiles/blame/BlameServlet.java
@@ -15,7 +15,6 @@
 package com.google.gitiles.blame;
 
 import static com.google.common.base.Preconditions.checkNotNull;
-import static javax.servlet.http.HttpServletResponse.SC_NOT_FOUND;
 
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
@@ -29,6 +28,8 @@
 import com.google.gitiles.GitilesAccess;
 import com.google.gitiles.GitilesView;
 import com.google.gitiles.Renderer;
+import com.google.gitiles.GitilesRequestFailureException;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
 import com.google.gitiles.ViewFilter;
 import com.google.gitiles.blame.cache.BlameCache;
 import com.google.gitiles.blame.cache.Region;
@@ -159,8 +160,7 @@
     RevCommit currCommit = rw.parseCommit(view.getRevision().getId());
     ObjectId currCommitBlobId = resolveBlob(view, rw, currCommit);
     if (currCommitBlobId == null) {
-      res.setStatus(SC_NOT_FOUND);
-      return null;
+      throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
     }
 
     ObjectId lastCommit = cache.findLastCommit(repo, currCommit, view.getPathPart());
@@ -182,8 +182,7 @@
 
     List<Region> regions = cache.get(repo, lastCommit, view.getPathPart());
     if (regions.isEmpty()) {
-      res.setStatus(SC_NOT_FOUND);
-      return null;
+      throw new GitilesRequestFailureException(FailureReason.BLAME_REGION_NOT_FOUND);
     }
     return new RegionResult(regions, lastCommitBlobId);
   }
diff --git a/java/com/google/gitiles/doc/DocServlet.java b/java/com/google/gitiles/doc/DocServlet.java
index 24f8d4b..509f460 100644
--- a/java/com/google/gitiles/doc/DocServlet.java
+++ b/java/com/google/gitiles/doc/DocServlet.java
@@ -32,6 +32,8 @@
 import com.google.gitiles.GitilesAccess;
 import com.google.gitiles.GitilesView;
 import com.google.gitiles.Renderer;
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
+import com.google.gitiles.GitilesRequestFailureException;
 import com.google.gitiles.ViewFilter;
 import com.google.gitiles.doc.html.StreamHtmlBuilder;
 import java.io.IOException;
@@ -86,8 +88,7 @@
   protected void doGetHtml(HttpServletRequest req, HttpServletResponse res) throws IOException {
     MarkdownConfig cfg = MarkdownConfig.get(getAccess(req).getConfig());
     if (!cfg.render) {
-      res.setStatus(SC_NOT_FOUND);
-      return;
+      throw new GitilesRequestFailureException(FailureReason.MARKDOWN_NOT_ENABLED);
     }
 
     GitilesView view = ViewFilter.getView(req);
@@ -99,14 +100,12 @@
       try {
         root = rw.parseTree(view.getRevision().getId());
       } catch (IncorrectObjectTypeException e) {
-        res.setStatus(SC_NOT_FOUND);
-        return;
+        throw new GitilesRequestFailureException(FailureReason.INCORRECT_OBJECT_TYPE);
       }
 
       MarkdownFile srcmd = findFile(rw, root, path);
       if (srcmd == null) {
-        res.setStatus(SC_NOT_FOUND);
-        return;
+        throw new GitilesRequestFailureException(FailureReason.OBJECT_NOT_FOUND);
       }
 
       MarkdownFile navmd = findNavbar(rw, root, path);
@@ -125,9 +124,6 @@
       } catch (LargeObjectException.ExceedsLimit errBig) {
         fileTooBig(res, view, errBig);
         return;
-      } catch (IOException err) {
-        readError(res, view, err);
-        return;
       }
 
       MarkdownToHtml.Builder fmt =
@@ -280,29 +276,12 @@
       HttpServletResponse res, GitilesView view, LargeObjectException.ExceedsLimit errBig)
       throws IOException {
     if (view.getType() == GitilesView.Type.ROOTED_DOC) {
-      log.error(
-          String.format(
-              "markdown too large: %s/%s %s %s: %s",
-              view.getHostName(),
-              view.getRepositoryName(),
-              view.getRevision(),
-              view.getPathPart(),
-              errBig.getMessage()));
-      res.setStatus(SC_INTERNAL_SERVER_ERROR);
+      throw new GitilesRequestFailureException(FailureReason.OBJECT_TOO_LARGE);
     } else {
       res.sendRedirect(GitilesView.show().copyFrom(view).toUrl());
     }
   }
 
-  private static void readError(HttpServletResponse res, GitilesView view, IOException err) {
-    log.error(
-        String.format(
-            "cannot load markdown %s/%s %s %s",
-            view.getHostName(), view.getRepositoryName(), view.getRevision(), view.getPathPart()),
-        err);
-    res.setStatus(SC_INTERNAL_SERVER_ERROR);
-  }
-
   private static class MarkdownFile {
     final String path;
     final ObjectId id;
diff --git a/javatests/com/google/gitiles/DefaultErrorHandlingFilterTest.java b/javatests/com/google/gitiles/DefaultErrorHandlingFilterTest.java
new file mode 100644
index 0000000..6832658
--- /dev/null
+++ b/javatests/com/google/gitiles/DefaultErrorHandlingFilterTest.java
@@ -0,0 +1,43 @@
+package com.google.gitiles;
+
+import static com.google.common.truth.Truth.assertThat;
+import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;
+
+import com.google.gitiles.GitilesRequestFailureException.FailureReason;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import org.eclipse.jgit.http.server.glue.MetaFilter;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class DefaultErrorHandlingFilterTest {
+  private final MetaFilter mf = new MetaFilter();
+
+  @Before
+  public void setUp() {
+    mf.serve("*").through(new DefaultErrorHandlingFilter()).with(new TestServlet());
+  }
+
+  @Test
+  public void renderError() throws Exception {
+    FakeHttpServletRequest req = FakeHttpServletRequest.newRequest();
+    req.setPathInfo("/");
+    FakeHttpServletResponse resp = new FakeHttpServletResponse();
+    mf.doFilter(req, resp, (unusedReq, unusedResp) -> {});
+
+    assertThat(resp.getStatus()).isEqualTo(SC_BAD_REQUEST);
+    assertThat(resp.getHeader(DefaultErrorHandlingFilter.GITILES_ERROR))
+        .isEqualTo("INCORECT_PARAMETER");
+  }
+
+  private static class TestServlet extends HttpServlet {
+    @Override
+    protected void doGet(HttpServletRequest req, HttpServletResponse res) {
+      throw new GitilesRequestFailureException(FailureReason.INCORECT_PARAMETER);
+    }
+  }
+}
diff --git a/javatests/com/google/gitiles/MoreAssert.java b/javatests/com/google/gitiles/MoreAssert.java
new file mode 100644
index 0000000..bd80d69
--- /dev/null
+++ b/javatests/com/google/gitiles/MoreAssert.java
@@ -0,0 +1,38 @@
+// Copyright 2019 Google LLC
+//
+// 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
+//
+//     https://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 com.google.gitiles;
+
+/** Assertion methods for Gitiles. */
+public class MoreAssert {
+  private MoreAssert() {}
+
+  /** Simple version of assertThrows that will be introduced in JUnit 4.13. */
+  public static <T extends Throwable> T assertThrows(Class<T> expected, ThrowingRunnable r) {
+    try {
+      r.run();
+      throw new AssertionError("Expected " + expected.getSimpleName() + " to be thrown");
+    } catch (Throwable actual) {
+      if (expected.isAssignableFrom(actual.getClass())) {
+        return (T) actual;
+      }
+      throw new AssertionError(
+          "Expected " + expected.getSimpleName() + ", but got " + actual.getClass().getSimpleName(),
+          actual);
+    }
+  }
+
+  public interface ThrowingRunnable {
+    void run() throws Throwable;
+  }
+}
diff --git a/javatests/com/google/gitiles/ViewFilterTest.java b/javatests/com/google/gitiles/ViewFilterTest.java
index 2a8cb65..d25b6cf 100644
--- a/javatests/com/google/gitiles/ViewFilterTest.java
+++ b/javatests/com/google/gitiles/ViewFilterTest.java
@@ -16,6 +16,7 @@
 
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.common.truth.Truth.assertWithMessage;
+import static com.google.gitiles.MoreAssert.assertThrows;
 
 import com.google.common.net.HttpHeaders;
 import com.google.gitiles.GitilesView.Type;
@@ -45,8 +46,8 @@
   public void noCommand() throws Exception {
     assertThat(getView("/").getType()).isEqualTo(Type.HOST_INDEX);
     assertThat(getView("/repo").getType()).isEqualTo(Type.REPOSITORY_INDEX);
-    assertThat(getView("/repo/+")).isNull();
-    assertThat(getView("/repo/+/")).isNull();
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+/"));
   }
 
   @Test
@@ -136,8 +137,8 @@
   public void describe() throws Exception {
     GitilesView view;
 
-    assertThat(getView("/repo/+describe")).isNull();
-    assertThat(getView("/repo/+describe/")).isNull();
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+describe"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+describe/"));
 
     view = getView("/repo/+describe/deadbeef");
     assertThat(view.getType()).isEqualTo(Type.DESCRIBE);
@@ -184,7 +185,7 @@
     assertThat(view.getRevision().getId()).isEqualTo(stable);
     assertThat(view.getPathPart()).isNull();
 
-    assertThat(getView("/repo/+show/stable..master")).isNull();
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+show/stable..master"));
   }
 
   @Test
@@ -250,7 +251,7 @@
     assertThat(view.getRevision().getId()).isEqualTo(master);
     assertThat(view.getPathPart()).isEqualTo("foo/bar");
 
-    assertThat(getView("/repo/+show/stable..master/foo")).isNull();
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+show/stable..master/foo"));
   }
 
   @Test
@@ -279,7 +280,7 @@
     assertThat(view.getRevision().getId()).isEqualTo(master);
     assertThat(view.getPathPart()).isEqualTo("foo/bar.md");
 
-    assertThat(getView("/repo/+doc/stable..master/foo")).isNull();
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+doc/stable..master/foo"));
   }
 
   @Test
@@ -288,10 +289,10 @@
     assertThat(getView("//").getType()).isEqualTo(Type.HOST_INDEX);
     assertThat(getView("//repo").getType()).isEqualTo(Type.REPOSITORY_INDEX);
     assertThat(getView("//repo//").getType()).isEqualTo(Type.REPOSITORY_INDEX);
-    assertThat(getView("/repo/+//master")).isNull();
-    assertThat(getView("/repo/+/refs//heads//master")).isNull();
-    assertThat(getView("/repo/+//master//")).isNull();
-    assertThat(getView("/repo/+//master/foo//bar")).isNull();
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+//master"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+/refs//heads//master"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+//master//"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+//master/foo//bar"));
   }
 
   @Test
@@ -420,13 +421,13 @@
     repo.branch("refs/heads/branch").commit().create();
     GitilesView view;
 
-    assertThat(getView("/repo/+archive")).isNull();
-    assertThat(getView("/repo/+archive/")).isNull();
-    assertThat(getView("/repo/+archive/master..branch")).isNull();
-    assertThat(getView("/repo/+archive/master.foo")).isNull();
-    assertThat(getView("/repo/+archive/master.zip")).isNull();
-    assertThat(getView("/repo/+archive/master/.tar.gz")).isNull();
-    assertThat(getView("/repo/+archive/master/foo/.tar.gz")).isNull();
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+archive"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+archive/"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+archive/master..branch"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+archive/master.foo"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+archive/master.zip"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+archive/master/.tar.gz"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+archive/master/foo/.tar.gz"));
 
     view = getView("/repo/+archive/master.tar.gz");
     assertThat(view.getType()).isEqualTo(Type.ARCHIVE);
@@ -462,10 +463,10 @@
     repo.branch("refs/heads/branch").commit().create();
     GitilesView view;
 
-    assertThat(getView("/repo/+blame")).isNull();
-    assertThat(getView("/repo/+blame/")).isNull();
-    assertThat(getView("/repo/+blame/master")).isNull();
-    assertThat(getView("/repo/+blame/master..branch")).isNull();
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+blame"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+blame/"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+blame/master"));
+    assertThrows(GitilesRequestFailureException.class, () -> getView("/repo/+blame/master..branch"));
 
     view = getView("/repo/+blame/master/foo/bar");
     assertThat(view.getType()).isEqualTo(Type.BLAME);