diff --git a/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap b/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap
index 2c64d0662fa0..749933aa4ab2 100644
--- a/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap
+++ b/lighthouse-cli/test/cli/__snapshots__/index-test.js.snap
@@ -102,6 +102,9 @@ Object {
     Object {
       "path": "metrics",
     },
+    Object {
+      "path": "offline-start-url",
+    },
     Object {
       "path": "manual/pwa-cross-browser",
     },
@@ -820,6 +823,11 @@ Object {
           "id": "works-offline",
           "weight": 5,
         },
+        Object {
+          "group": "pwa-fast-reliable",
+          "id": "offline-start-url",
+          "weight": 1,
+        },
         Object {
           "group": "pwa-installable",
           "id": "is-on-https",
@@ -833,7 +841,7 @@ Object {
         Object {
           "group": "pwa-installable",
           "id": "webapp-install-banner",
-          "weight": 3,
+          "weight": 2,
         },
         Object {
           "group": "pwa-engaging",
diff --git a/lighthouse-cli/test/smokehouse/pwa-expectations.js b/lighthouse-cli/test/smokehouse/pwa-expectations.js
index e8042e40618c..dc61ca6b09c6 100644
--- a/lighthouse-cli/test/smokehouse/pwa-expectations.js
+++ b/lighthouse-cli/test/smokehouse/pwa-expectations.js
@@ -38,6 +38,9 @@ module.exports = [
       'works-offline': {
         score: 1,
       },
+      'offline-start-url': {
+        score: 1,
+      },
       'viewport': {
         score: 1,
       },
@@ -95,6 +98,9 @@ module.exports = [
       'works-offline': {
         score: 0,
       },
+      'offline-start-url': {
+        score: 1,
+      },
       'viewport': {
         score: 1,
       },
diff --git a/lighthouse-cli/test/smokehouse/pwa2-expectations.js b/lighthouse-cli/test/smokehouse/pwa2-expectations.js
index 36be890b3c4b..28857e8bde56 100644
--- a/lighthouse-cli/test/smokehouse/pwa2-expectations.js
+++ b/lighthouse-cli/test/smokehouse/pwa2-expectations.js
@@ -32,6 +32,9 @@ module.exports = [
       'works-offline': {
         score: 1,
       },
+      'offline-start-url': {
+        score: 1,
+      },
       'viewport': {
         score: 1,
       },
@@ -89,6 +92,9 @@ module.exports = [
       'works-offline': {
         score: 1,
       },
+      'offline-start-url': {
+        score: 1,
+      },
       'viewport': {
         score: 1,
       },
diff --git a/lighthouse-cli/test/smokehouse/pwa3-expectations.js b/lighthouse-cli/test/smokehouse/pwa3-expectations.js
index f28cdbc5fa87..6554e9fa3d62 100644
--- a/lighthouse-cli/test/smokehouse/pwa3-expectations.js
+++ b/lighthouse-cli/test/smokehouse/pwa3-expectations.js
@@ -30,6 +30,9 @@ module.exports = [
       'works-offline': {
         score: 1,
       },
+      'offline-start-url': {
+        score: 1,
+      },
       'viewport': {
         score: 1,
       },
diff --git a/lighthouse-core/audits/multi-check-audit.js b/lighthouse-core/audits/multi-check-audit.js
index fb878279948c..35e62a59f3c8 100644
--- a/lighthouse-core/audits/multi-check-audit.js
+++ b/lighthouse-core/audits/multi-check-audit.js
@@ -23,7 +23,7 @@ class MultiCheckAudit extends Audit {
   }
 
   /**
-   * @param {{failures: Array<string>, warnings?: Array<string>, manifestValues?: LH.Artifacts.ManifestValues}} result
+   * @param {{failures: Array<string>, manifestValues?: LH.Artifacts.ManifestValues}} result
    * @return {LH.Audit.Product}
    */
   static createAuditProduct(result) {
@@ -57,7 +57,6 @@ class MultiCheckAudit extends Audit {
     return {
       rawValue: true,
       details,
-      warnings: result.warnings,
     };
   }
 
@@ -66,7 +65,7 @@ class MultiCheckAudit extends Audit {
   /**
    * @param {LH.Artifacts} artifacts
    * @param {LH.Audit.Context} context
-   * @return {Promise<{failures: Array<string>, warnings?: Array<string>, manifestValues?: LH.Artifacts.ManifestValues}>}
+   * @return {Promise<{failures: Array<string>, manifestValues?: LH.Artifacts.ManifestValues}>}
    */
   static audit_(artifacts, context) {
     throw new Error('audit_ unimplemented');
diff --git a/lighthouse-core/audits/offline-start-url.js b/lighthouse-core/audits/offline-start-url.js
new file mode 100644
index 000000000000..fb6f0b2c8799
--- /dev/null
+++ b/lighthouse-core/audits/offline-start-url.js
@@ -0,0 +1,49 @@
+/**
+ * @license Copyright 2018 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.
+ */
+'use strict';
+
+const Audit = require('./audit.js');
+
+class OfflineStartUrl extends Audit {
+  /**
+   * @return {LH.Audit.Meta}
+   */
+  static get meta() {
+    return {
+      id: 'offline-start-url',
+      title: 'start_url responds with a 200 when offline',
+      failureTitle: 'start_url does not respond with a 200 when offline',
+      description: 'A service worker enables your web app to be reliable in unpredictable network conditions. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/http-200-when-offline).',
+      requiredArtifacts: ['Manifest', 'StartUrl'],
+    };
+  }
+
+  /**
+   * @param {LH.Artifacts} artifacts
+   * @return {LH.Audit.Product}
+   */
+  static audit(artifacts) {
+    // StartUrl gatherer will give explanations for failures, but need to take manifest parsing
+    // warnings from the manifest itself (e.g. invalid `start_url`, so fell back to document URL).
+    const warnings = [];
+    const manifest = artifacts.Manifest;
+    if (manifest && manifest.value && manifest.value.start_url.warning) {
+      const manifestWarning = manifest.value.start_url.warning;
+      warnings.push('We couldn\'t read the start_url from the manifest. As a result, the ' +
+          `start_url was assumed to be the document's URL. Error message: '${manifestWarning}'.`);
+    }
+
+    const hasOfflineStartUrl = artifacts.StartUrl.statusCode === 200;
+
+    return {
+      rawValue: hasOfflineStartUrl,
+      explanation: artifacts.StartUrl.explanation,
+      warnings,
+    };
+  }
+}
+
+module.exports = OfflineStartUrl;
diff --git a/lighthouse-core/audits/webapp-install-banner.js b/lighthouse-core/audits/webapp-install-banner.js
index 804238fb8f6d..e9020a368a75 100644
--- a/lighthouse-core/audits/webapp-install-banner.js
+++ b/lighthouse-core/audits/webapp-install-banner.js
@@ -41,7 +41,7 @@ class WebappInstallBanner extends MultiCheckAudit {
       description: 'Browsers can proactively prompt users to add your app to their homescreen, ' +
           'which can lead to higher engagement. ' +
           '[Learn more](https://developers.google.com/web/tools/lighthouse/audits/install-prompt).',
-      requiredArtifacts: ['URL', 'ServiceWorker', 'Manifest', 'StartUrl'],
+      requiredArtifacts: ['URL', 'ServiceWorker', 'Manifest'],
     };
   }
 
@@ -94,55 +94,20 @@ class WebappInstallBanner extends MultiCheckAudit {
     return failures;
   }
 
-  /**
-   * @param {LH.Artifacts} artifacts
-   * @return {{failures: Array<string>, warnings: Array<string>}}
-   */
-  static assessOfflineStartUrl(artifacts) {
-    const failures = [];
-    const warnings = [];
-    const hasOfflineStartUrl = artifacts.StartUrl.statusCode === 200;
-
-    if (!hasOfflineStartUrl) {
-      failures.push('Service worker does not successfully serve the manifest\'s start_url');
-      if (artifacts.StartUrl.explanation) {
-        failures.push(artifacts.StartUrl.explanation);
-      }
-    }
-
-    if (artifacts.StartUrl.explanation) {
-      warnings.push(artifacts.StartUrl.explanation);
-    }
-
-    return {failures, warnings};
-  }
-
   /**
    * @param {LH.Artifacts} artifacts
    * @param {LH.Audit.Context} context
-   * @return {Promise<{failures: Array<string>, warnings: Array<string>, manifestValues: LH.Artifacts.ManifestValues}>}
+   * @return {Promise<{failures: Array<string>, manifestValues: LH.Artifacts.ManifestValues}>}
    */
   static async audit_(artifacts, context) {
-    /** @type {Array<string>} */
-    let offlineFailures = [];
-    /** @type {Array<string>} */
-    let offlineWarnings = [];
-
     const manifestValues = await ManifestValues.request(artifacts.Manifest, context);
     const manifestFailures = WebappInstallBanner.assessManifest(manifestValues);
     const swFailures = WebappInstallBanner.assessServiceWorker(artifacts);
-    if (!swFailures.length) {
-      const {failures, warnings} = WebappInstallBanner.assessOfflineStartUrl(artifacts);
-      offlineFailures = failures;
-      offlineWarnings = warnings;
-    }
 
     return {
-      warnings: offlineWarnings,
       failures: [
         ...manifestFailures,
         ...swFailures,
-        ...offlineFailures,
       ],
       manifestValues,
     };
diff --git a/lighthouse-core/config/default-config.js b/lighthouse-core/config/default-config.js
index d26faa2f7a18..8ddbf24b2d57 100644
--- a/lighthouse-core/config/default-config.js
+++ b/lighthouse-core/config/default-config.js
@@ -132,6 +132,7 @@ const defaultConfig = {
     'font-display',
     'network-requests',
     'metrics',
+    'offline-start-url',
     'manual/pwa-cross-browser',
     'manual/pwa-page-transitions',
     'manual/pwa-each-page-has-url',
@@ -334,10 +335,11 @@ const defaultConfig = {
         // Fast and Reliable
         {id: 'load-fast-enough-for-pwa', weight: 7, group: 'pwa-fast-reliable'},
         {id: 'works-offline', weight: 5, group: 'pwa-fast-reliable'},
+        {id: 'offline-start-url', weight: 1, group: 'pwa-fast-reliable'},
         // Installable
         {id: 'is-on-https', weight: 2, group: 'pwa-installable'},
         {id: 'service-worker', weight: 1, group: 'pwa-installable'},
-        {id: 'webapp-install-banner', weight: 3, group: 'pwa-installable'},
+        {id: 'webapp-install-banner', weight: 2, group: 'pwa-installable'},
         // Engaging
         {id: 'redirects-http', weight: 2, group: 'pwa-engaging'},
         {id: 'splash-screen', weight: 1, group: 'pwa-engaging'},
diff --git a/lighthouse-core/gather/gatherers/start-url.js b/lighthouse-core/gather/gatherers/start-url.js
index 9d7c59ec78ef..1d42543acb82 100644
--- a/lighthouse-core/gather/gatherers/start-url.js
+++ b/lighthouse-core/gather/gatherers/start-url.js
@@ -7,7 +7,8 @@
 
 const Gatherer = require('./gatherer');
 const manifestParser = require('../../lib/manifest-parser');
-const Driver = require('../driver.js'); // eslint-disable-line no-unused-vars
+
+/** @typedef {import('../driver.js')} Driver */
 
 class StartUrl extends Gatherer {
   /**
@@ -29,13 +30,13 @@ class StartUrl extends Gatherer {
 
         return this._attemptManifestFetch(passContext.driver, startUrlInfo.startUrl);
       }).catch(() => {
-        return {statusCode: -1, explanation: 'Unable to fetch start URL via service worker'};
+        return {statusCode: -1, explanation: 'Unable to fetch start URL via service worker.'};
       });
   }
 
   /**
    * Read the parsed manifest and return failure reasons or the startUrl
-   * @param {?{value?: {start_url: {value?: string, warning?: string}}, warning?: string}} manifest
+   * @param {?{value?: {start_url: {value: string, warning?: string}}, warning?: string}} manifest
    * @return {{isReadFailure: true, reason: string}|{isReadFailure: false, startUrl: string}}
    */
   _readManifestStartUrl(manifest) {
@@ -43,19 +44,13 @@ class StartUrl extends Gatherer {
       const detailedMsg = manifest && manifest.warning;
 
       if (detailedMsg) {
-        return {isReadFailure: true, reason: `Error fetching web app manifest: ${detailedMsg}`};
+        return {isReadFailure: true, reason: `Error fetching web app manifest: ${detailedMsg}.`};
       } else {
-        return {isReadFailure: true, reason: `No usable web app manifest found on page`};
+        return {isReadFailure: true, reason: `No usable web app manifest found on page.`};
       }
     }
 
-    // Even if the start URL had an error, the browser will still supply a fallback URL.
-    // Therefore, we only set the warning here and continue with the fetch.
-    if (manifest.value.start_url.warning) {
-      return {isReadFailure: true, reason: manifest.value.start_url.warning};
-    }
-
-    // @ts-ignore - TODO(bckenny): should actually be testing value above, not warning
+    // Even if the start URL had a parser warning, the browser will still supply a fallback URL.
     return {isReadFailure: false, startUrl: manifest.value.start_url.value};
   }
 
@@ -70,7 +65,7 @@ class StartUrl extends Gatherer {
     // Wait up to 3s to get a matched network request from the fetch() to work
     const timeoutPromise = new Promise(resolve =>
       setTimeout(
-        () => resolve({statusCode: -1, explanation: 'Timed out waiting for fetched start_url'}),
+        () => resolve({statusCode: -1, explanation: 'Timed out waiting for fetched start_url.'}),
         3000
       )
     );
@@ -88,7 +83,7 @@ class StartUrl extends Gatherer {
         if (!response.fromServiceWorker) {
           return resolve({
             statusCode: -1,
-            explanation: 'Unable to fetch start URL via service worker',
+            explanation: 'Unable to fetch start URL via service worker.',
           });
         }
         // Successful SW-served fetch of the start_URL
diff --git a/lighthouse-core/lib/manifest-parser.js b/lighthouse-core/lib/manifest-parser.js
index 7468583b8052..34262c1a7e89 100644
--- a/lighthouse-core/lib/manifest-parser.js
+++ b/lighthouse-core/lib/manifest-parser.js
@@ -115,6 +115,7 @@ function checkSameOrigin(url1, url2) {
  * @param {*} jsonInput
  * @param {string} manifestUrl
  * @param {string} documentUrl
+ * @return {{raw: any, value: string, warning?: string}}
  */
 function parseStartUrl(jsonInput, manifestUrl, documentUrl) {
   const raw = jsonInput.start_url;
@@ -127,10 +128,18 @@ function parseStartUrl(jsonInput, manifestUrl, documentUrl) {
       warning: 'ERROR: start_url string empty',
     };
   }
-  const parsedAsString = parseString(raw);
-  if (!parsedAsString.value) {
-    parsedAsString.value = documentUrl;
-    return parsedAsString;
+  if (raw === undefined) {
+    return {
+      raw,
+      value: documentUrl,
+    };
+  }
+  if (typeof raw !== 'string') {
+    return {
+      raw,
+      value: documentUrl,
+      warning: 'ERROR: expected a string.',
+    };
   }
 
   // 8.10(4) - construct URL with raw as input and manifestUrl as the base.
diff --git a/lighthouse-core/test/audits/offline-start-url-test.js b/lighthouse-core/test/audits/offline-start-url-test.js
new file mode 100644
index 000000000000..2d5c5597e216
--- /dev/null
+++ b/lighthouse-core/test/audits/offline-start-url-test.js
@@ -0,0 +1,73 @@
+/**
+ * @license Copyright 2018 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.
+ */
+'use strict';
+
+const assert = require('assert');
+const OfflineStartUrlAudit = require('../../audits/offline-start-url.js');
+const manifestParser = require('../../lib/manifest-parser.js');
+
+/* eslint-env jest */
+
+function generateMockAuditContext() {
+  return {
+    computedCache: new Map(),
+  };
+}
+function getManifest(manifest) {
+  const documentUrl = 'https://example.com/';
+  const manifestUrl = `${documentUrl}manifest.json`;
+
+  return manifestParser(JSON.stringify(manifest), manifestUrl, documentUrl);
+}
+
+describe('Offline start_url audit', () => {
+  it('fails if start_url is not fetched', async () => {
+    const explanation = 'Unable to fetch start URL via service worker.';
+
+    const artifacts = {
+      StartUrl: {
+        statusCode: -1,
+        explanation,
+      },
+    };
+    const context = generateMockAuditContext();
+
+    const result = await OfflineStartUrlAudit.audit(artifacts, context);
+    assert.strictEqual(result.rawValue, false);
+    assert.strictEqual(result.explanation, explanation);
+    assert.strictEqual(result.warnings.length, 0);
+  });
+
+  it('passes if start_url is fetched', async () => {
+    const artifacts = {
+      StartUrl: {statusCode: 200},
+    };
+    const context = generateMockAuditContext();
+
+    const result = await OfflineStartUrlAudit.audit(artifacts, context);
+    assert.strictEqual(result.rawValue, true);
+    assert.strictEqual(result.explanation, undefined);
+    assert.strictEqual(result.warnings.length, 0);
+  });
+
+  it('warns if there was a manifest start_url parsing error', async () => {
+    const manifest = {
+      start_url: 'https://evil.com/',
+    };
+
+    const artifacts = {
+      Manifest: getManifest(manifest),
+      StartUrl: {statusCode: 200},
+    };
+    const context = generateMockAuditContext();
+
+    const result = await OfflineStartUrlAudit.audit(artifacts, context);
+    assert.strictEqual(result.rawValue, true);
+    assert.strictEqual(result.explanation, undefined);
+    assert.strictEqual(result.warnings.length, 1);
+    assert.ok(result.warnings[0].includes('start_url must be same-origin as document'));
+  });
+});
diff --git a/lighthouse-core/test/audits/webapp-install-banner-test.js b/lighthouse-core/test/audits/webapp-install-banner-test.js
index 1ed204e5ee09..9e9d4b2b6682 100644
--- a/lighthouse-core/test/audits/webapp-install-banner-test.js
+++ b/lighthouse-core/test/audits/webapp-install-banner-test.js
@@ -25,7 +25,6 @@ function generateMockArtifacts(src = manifestSrc) {
         scriptURL: 'https://example.com/sw.js',
       }],
     },
-    StartUrl: {statusCode: 200},
     URL: {finalUrl: 'https://example.com'},
   }));
   return clonedArtifacts;
@@ -151,7 +150,6 @@ describe('PWA: webapp install banner audit', () => {
   it('fails if page had no SW', () => {
     const artifacts = generateMockArtifacts();
     artifacts.ServiceWorker.versions = [];
-    artifacts.StartUrl = {statusCode: -1};
     const context = generateMockAuditContext();
 
     return WebappInstallBannerAudit.audit(artifacts, context).then(result => {
@@ -161,28 +159,4 @@ describe('PWA: webapp install banner audit', () => {
       assert.strictEqual(failures.length, 1, failures);
     });
   });
-
-  it('fails if start_url is not cached', () => {
-    const artifacts = generateMockArtifacts();
-    artifacts.StartUrl = {statusCode: -1};
-    const context = generateMockAuditContext();
-
-    return WebappInstallBannerAudit.audit(artifacts, context).then(result => {
-      assert.strictEqual(result.rawValue, false);
-      assert.ok(result.explanation.includes('start_url'), result.explanation);
-      const failures = result.details.items[0].failures;
-      assert.strictEqual(failures.length, 1, failures);
-    });
-  });
-
-  it('includes warning from start_url', () => {
-    const artifacts = generateMockArtifacts();
-    artifacts.StartUrl = {statusCode: 200, explanation: 'Warning!'};
-    const context = generateMockAuditContext();
-
-    return WebappInstallBannerAudit.audit(artifacts, context).then(result => {
-      assert.strictEqual(result.rawValue, true);
-      assert.equal(result.warnings[0], 'Warning!');
-    });
-  });
 });
diff --git a/lighthouse-core/test/gather/gatherers/start-url-test.js b/lighthouse-core/test/gather/gatherers/start-url-test.js
index 6924a3033392..df9b0fd3710f 100644
--- a/lighthouse-core/test/gather/gatherers/start-url-test.js
+++ b/lighthouse-core/test/gather/gatherers/start-url-test.js
@@ -82,7 +82,7 @@ describe('Start-url gatherer', () => {
       assert.ok(artifactWithQueryString.explanation, 'did not set debug string');
       assert.equal(artifactWithResponseNotFromSW.statusCode, -1);
       assert.equal(artifactWithResponseNotFromSW.explanation,
-          'Unable to fetch start URL via service worker');
+          'Unable to fetch start URL via service worker.');
     });
   });
 
@@ -120,7 +120,7 @@ describe('Start-url gatherer', () => {
     return startUrlGatherer.afterPass(options, tracingData)
       .then(artifact => {
         assert.equal(artifact.explanation,
-          `No usable web app manifest found on page`);
+          `No usable web app manifest found on page.`);
       });
   });
 
@@ -141,11 +141,11 @@ describe('Start-url gatherer', () => {
       .then(artifact => {
         assert.equal(artifact.explanation,
           `Error fetching web app manifest: ERROR: file isn't valid JSON: ` +
-          `SyntaxError: Unexpected token h in JSON at position 1`);
+          `SyntaxError: Unexpected token h in JSON at position 1.`);
       });
   });
 
-  it('returns a explanation when start_url cannot be found', () => {
+  it('times out when a start_url is too slow to respond', () => {
     const startUrlGatherer = new StartUrlGatherer();
     const options = {
       url: 'https://ifixit-pwa.appspot.com/',
@@ -154,20 +154,7 @@ describe('Start-url gatherer', () => {
 
     return startUrlGatherer.afterPass(options, tracingData)
       .then(artifact => {
-        assert.equal(artifact.explanation, 'ERROR: start_url string empty');
-      });
-  });
-
-  it('returns an error when origin is not the same', () => {
-    const startUrlGatherer = new StartUrlGatherer();
-    const options = {
-      url: 'https://ifixit-pwa.appspot.com/',
-      driver: wrapSendCommand(mockDriver, 'https://not-same-origin.com/'),
-    };
-
-    return startUrlGatherer.afterPass(options, tracingData)
-      .then(artifact => {
-        assert.equal(artifact.explanation, 'ERROR: start_url must be same-origin as document');
+        assert.equal(artifact.explanation, 'Timed out waiting for fetched start_url.');
       });
   });
 });
diff --git a/lighthouse-core/test/lib/manifest-parser-test.js b/lighthouse-core/test/lib/manifest-parser-test.js
index 5a0b37c0bb7f..f07d83d66925 100644
--- a/lighthouse-core/test/lib/manifest-parser-test.js
+++ b/lighthouse-core/test/lib/manifest-parser-test.js
@@ -190,7 +190,7 @@ describe('Manifest Parser', function() {
   describe('start_url parsing', () => {
     /* eslint-disable camelcase */
     // 8.10(3)
-    it('falls back to document URL and issues a warning for an invalid value', () => {
+    it('falls back to document URL and issues a warning for a non-string', () => {
       const manifestSrc = JSON.stringify({
         start_url: {},
       });
@@ -203,7 +203,7 @@ describe('Manifest Parser', function() {
       assert.equal(parsedUrl.value, docUrl);
     });
 
-    it('falls back to document URL and issues a warning for an invalid value', () => {
+    it('falls back to document URL and issues a warning for a non-string', () => {
       const manifestSrc = JSON.stringify({
         start_url: 6,
       });
diff --git a/lighthouse-core/test/report/html/renderer/category-renderer-test.js b/lighthouse-core/test/report/html/renderer/category-renderer-test.js
index 0d4cb0751e2a..27c1947bcd1d 100644
--- a/lighthouse-core/test/report/html/renderer/category-renderer-test.js
+++ b/lighthouse-core/test/report/html/renderer/category-renderer-test.js
@@ -229,7 +229,7 @@ describe('CategoryRenderer', () => {
       const manualAudits = elem.querySelectorAll('.lh-audit-group--manual .lh-audit');
 
       assert.equal(passedAudits.length, 4);
-      assert.equal(failedAudits.length, 7);
+      assert.equal(failedAudits.length, 8);
       assert.equal(manualAudits.length, 3);
     });
 
@@ -242,7 +242,7 @@ describe('CategoryRenderer', () => {
       const failedAudits = elem.querySelectorAll('.lh-failed-audits .lh-audit');
 
       assert.equal(passedAudits.length, 0);
-      assert.equal(failedAudits.length, 11);
+      assert.equal(failedAudits.length, 12);
 
       assert.equal(elem.querySelector('.lh-passed-audits-summary'), null);
     });
diff --git a/lighthouse-core/test/results/sample_v2.json b/lighthouse-core/test/results/sample_v2.json
index 7417f748c94d..424dc2862f4f 100644
--- a/lighthouse-core/test/results/sample_v2.json
+++ b/lighthouse-core/test/results/sample_v2.json
@@ -1048,6 +1048,15 @@
         ]
       }
     },
+    "offline-start-url": {
+      "id": "offline-start-url",
+      "title": "start_url does not respond with a 200 when offline",
+      "description": "A service worker enables your web app to be reliable in unpredictable network conditions. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/http-200-when-offline).",
+      "score": 0,
+      "scoreDisplayMode": "binary",
+      "rawValue": false,
+      "warnings": []
+    },
     "pwa-cross-browser": {
       "id": "pwa-cross-browser",
       "title": "Site works cross-browser",
@@ -2927,6 +2936,11 @@
           "weight": 5,
           "group": "pwa-fast-reliable"
         },
+        {
+          "id": "offline-start-url",
+          "weight": 1,
+          "group": "pwa-fast-reliable"
+        },
         {
           "id": "is-on-https",
           "weight": 2,
@@ -2939,7 +2953,7 @@
         },
         {
           "id": "webapp-install-banner",
-          "weight": 3,
+          "weight": 2,
           "group": "pwa-installable"
         },
         {
@@ -3652,6 +3666,12 @@
         "duration": 100,
         "entryType": "measure"
       },
+      {
+        "startTime": 0,
+        "name": "lh:audit:offline-start-url",
+        "duration": 100,
+        "entryType": "measure"
+      },
       {
         "startTime": 0,
         "name": "lh:audit:pwa-cross-browser",
diff --git a/proto/sample_v2_round_trip.json b/proto/sample_v2_round_trip.json
index ba8e2c4b39b0..0934f7b49ceb 100644
--- a/proto/sample_v2_round_trip.json
+++ b/proto/sample_v2_round_trip.json
@@ -1630,6 +1630,14 @@
             "scoreDisplayMode": "not_applicable", 
             "title": "`<object>` elements have `[alt]` text"
         }, 
+        "offline-start-url": {
+            "description": "A service worker enables your web app to be reliable in unpredictable network conditions. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/http-200-when-offline).", 
+            "id": "offline-start-url", 
+            "score": 0.0, 
+            "scoreDisplayMode": "binary", 
+            "title": "start_url does not respond with a 200 when offline", 
+            "warnings": []
+        }, 
         "offscreen-content-hidden": {
             "description": "Offscreen content is hidden with display: none or aria-hidden=true. [Learn more](https://developers.google.com/web/fundamentals/accessibility/how-to-review#try_it_with_a_screen_reader).", 
             "id": "offscreen-content-hidden", 
@@ -3041,6 +3049,11 @@
                     "id": "works-offline", 
                     "weight": 5.0
                 }, 
+                {
+                    "group": "pwa-fast-reliable", 
+                    "id": "offline-start-url", 
+                    "weight": 1.0
+                }, 
                 {
                     "group": "pwa-installable", 
                     "id": "is-on-https", 
@@ -3054,7 +3067,7 @@
                 {
                     "group": "pwa-installable", 
                     "id": "webapp-install-banner", 
-                    "weight": 3.0
+                    "weight": 2.0
                 }, 
                 {
                     "group": "pwa-engaging", 
@@ -3509,6 +3522,12 @@
                 "name": "lh:audit:metrics", 
                 "startTime": 0.0
             }, 
+            {
+                "duration": 100.0, 
+                "entryType": "measure", 
+                "name": "lh:audit:offline-start-url", 
+                "startTime": 0.0
+            }, 
             {
                 "duration": 100.0, 
                 "entryType": "measure",