diff --git a/demo/index.html b/demo/index.html
index d5ee156..245116f 100644
--- a/demo/index.html
+++ b/demo/index.html
@@ -66,6 +66,8 @@ <H1>this is a really big heading tag. 51 chars long even. this is a really big h
           <p> - List item</p>
           <p>Split breaks:</p>
           <p>1. List Item<br>2. List Item</p>
+          <a href="weird link">Bad Link</a>
+          <a href="https://google.com">Good Link (cross domain)</a>
         </textarea>
     </div>
   </div>
diff --git a/package-lock.json b/package-lock.json
index 3c918dd..eadbcb6 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -12287,6 +12287,17 @@
       "requires": {
         "node-fetch": "^1.0.1",
         "whatwg-fetch": ">=0.10.0"
+      },
+      "dependencies": {
+        "node-fetch": {
+          "version": "1.7.3",
+          "resolved": "https://registry.npmjs.org/node-fetch/-/node-fetch-1.7.3.tgz",
+          "integrity": "sha512-NhZ4CsKx7cYm2vSrBAr2PvFOe6sWDf0UYLRqA6svUYg7+/TSfVAu49jYC4BvQ4Sms9SZgdqGBgroqfDhJdTyKQ==",
+          "requires": {
+            "encoding": "^0.1.11",
+            "is-stream": "^1.0.1"
+          }
+        }
       }
     },
     "isstream": {
@@ -15285,13 +15296,9 @@
       "integrity": "sha512-YTzGAJOo/B6hkodeT5SKKHpOhAzjMfkUCCXjLJwjWk2F4/InIg+HbdH9kmT7bKpleDuqLZDTRy2OdNtAj0IVyQ=="
     },
     "node-fetch": {
-      "version": "1.7.3",
-      "resolved": "https://registry.npmjs.org/node-fetch/-/node-fetch-1.7.3.tgz",
-      "integrity": "sha512-NhZ4CsKx7cYm2vSrBAr2PvFOe6sWDf0UYLRqA6svUYg7+/TSfVAu49jYC4BvQ4Sms9SZgdqGBgroqfDhJdTyKQ==",
-      "requires": {
-        "encoding": "^0.1.11",
-        "is-stream": "^1.0.1"
-      }
+      "version": "2.1.2",
+      "resolved": "https://registry.npmjs.org/node-fetch/-/node-fetch-2.1.2.tgz",
+      "integrity": "sha1-q4hOjn5X44qUR1POxwb3iNF2i7U="
     },
     "node-forge": {
       "version": "0.7.5",
diff --git a/src/rules/__tests__/__snapshots__/valid-links.js.snap b/src/rules/__tests__/__snapshots__/valid-links.js.snap
new file mode 100644
index 0000000..9e0f400
--- /dev/null
+++ b/src/rules/__tests__/__snapshots__/valid-links.js.snap
@@ -0,0 +1,26 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`data returns the proper object 1`] = `
+Object {
+  "href": null,
+}
+`;
+
+exports[`form returns the proper object 1`] = `
+Array [
+  Object {
+    "dataKey": "href",
+    "disabledIf": [Function],
+    "label": "Ensure this link is correct.",
+  },
+  Object {
+    "checkbox": true,
+    "dataKey": "ignore",
+    "label": "Ignore this link in the future.",
+  },
+]
+`;
+
+exports[`message returns the proper message 1`] = `"This link could not be verified."`;
+
+exports[`why returns the proper why message 1`] = `"Links should not be broken."`;
diff --git a/src/rules/__tests__/valid-links.js b/src/rules/__tests__/valid-links.js
new file mode 100644
index 0000000..1e0aab7
--- /dev/null
+++ b/src/rules/__tests__/valid-links.js
@@ -0,0 +1,88 @@
+import rule from "../valid-links"
+
+let body, a
+
+beforeEach(() => {
+  body = document.createElement("body")
+  a = document.createElement("a")
+  body.appendChild(a)
+  a.textContent = "Link Text"
+  window.fetch = () => Promise.resolve({ ok: true })
+})
+
+describe("test", () => {
+  test("returns true if not A element", async () => {
+    expect(await rule.test(document.createElement("div"))).toBe(true)
+  })
+
+  test("returns true for valid links", async () => {
+    window.fetch = () => Promise.resolve({ ok: true })
+    a.setAttribute("href", "https://www.instructure.com/")
+    expect(await rule.test(a)).toBe(true)
+  })
+
+  test("returns false for invalid links", async () => {
+    window.fetch = () => Promise.resolve({ ok: false })
+    a.setAttribute("href", "http://something weird")
+    expect(await rule.test(a)).toBe(false)
+    a.setAttribute("href", "plaintext")
+    expect(await rule.test(a)).toBe(false)
+    window.fetch = () => Promise.reject(new Error())
+    a.setAttribute("href", "http://something-valid-but-not-reachable/123")
+    expect(await rule.test(a)).toBe(false)
+  })
+})
+
+describe("data", () => {
+  test("returns the proper object", () => {
+    expect(rule.data(a)).toMatchSnapshot()
+  })
+})
+
+describe("form", () => {
+  test("returns the proper object", () => {
+    expect(rule.form(a)).toMatchSnapshot()
+  })
+})
+
+describe("update", () => {
+  test("returns same element", () => {
+    expect(rule.update(a, {})).toBe(a)
+  })
+  test("does not change href if href does not change", () => {
+    const href = "http://example.com"
+    a.setAttribute("href", href)
+    expect(rule.update(a, { href })).toBe(a)
+  })
+  test("changes href if it has been changed", () => {
+    const href = "bad"
+    a.setAttribute("href", href)
+    rule.update(a, { href: "https://www.instructure.com/" })
+    expect(a.getAttribute("href")).toBe("https://www.instructure.com/")
+  })
+  test("does not change href if href does not change", () => {
+    const href = "http://example.com"
+    a.setAttribute("href", href)
+    expect(
+      rule.update(a, { ignore: true }).getAttribute("data-ignore-a11y-check")
+    ).toBe("true")
+  })
+})
+
+describe("rootNode", () => {
+  test("returns the parentNode of an element", () => {
+    expect(rule.rootNode(a).tagName).toBe("BODY")
+  })
+})
+
+describe("message", () => {
+  test("returns the proper message", () => {
+    expect(rule.message()).toMatchSnapshot()
+  })
+})
+
+describe("why", () => {
+  test("returns the proper why message", () => {
+    expect(rule.why()).toMatchSnapshot()
+  })
+})
diff --git a/src/rules/index.js b/src/rules/index.js
index 5f6df63..8605c80 100644
--- a/src/rules/index.js
+++ b/src/rules/index.js
@@ -10,6 +10,7 @@ import headingsSequence from "./headings-sequence"
 import imageAltLength from "./img-alt-length"
 import paragraphsForHeadings from "./paragraphs-for-headings"
 import listStructure from "./list-structure"
+import validLinks from "./valid-links"
 
 export default [
   imgAlt,
@@ -23,5 +24,6 @@ export default [
   headingsSequence,
   imageAltLength,
   paragraphsForHeadings,
-  listStructure
+  listStructure,
+  validLinks
 ]
diff --git a/src/rules/valid-links.js b/src/rules/valid-links.js
new file mode 100644
index 0000000..f7804d2
--- /dev/null
+++ b/src/rules/valid-links.js
@@ -0,0 +1,230 @@
+import formatMessage from "../format-message"
+
+/**
+ * How does this Link Checker work?
+ *
+ * This checker takes inspiration from JSONP,
+ * where cross domain requests are still valid
+ * even if they load from a 3rd party site
+ *
+ * 1. An iframe sandbox is created from a data url.
+ * 2. This iframe contains a script tag will create
+ *    a web worker.
+ * 3. The top frame sends the iframe the url in
+ *    question, and the frame creates the worker
+ *    with the url embeded in a `loadScripts` call.
+ * 4. If the script loads, it will fail silently
+ *    - If silent, the worker responds true (good)
+ *    - else the worker responds false (bad link)
+ *    - on timeout, the worker responds false
+ * 5. The top frame waits for the response and
+ *    removes the iframe.
+ *
+ * Note, as of writing, this does not work on
+ * non-chromium browsers. In that case, all links
+ * are flagged as bad with the message:
+ *   "This link could not be verified."
+ *
+ * It would also appear that jsdom (used for tests)
+ * cannot handle this as well.
+ */
+
+const isValidURL = url => {
+  try {
+    // the URL constructor is more accurate than regex
+    // but not supported in IE.
+    new URL(url)
+    return true
+  } catch (_) {
+    // If this does throw, either:
+    // 1. the url is invalid
+    // 2. the URL constructor is not there.
+    // The user will be prompted to check the link manually.
+    return false
+  }
+}
+
+const send = (type, payload, frame) =>
+  new Promise((resolve, reject) => {
+    const id = Math.random() + Date.now()
+    const message = JSON.stringify({ type, payload, id })
+
+    const handler = event => {
+      let obj = event.data
+      try {
+        if (typeof obj === "string") obj = JSON.parse(event.data)
+      } catch (e) {
+        return
+      }
+
+      const { error, response, id: returnedId } = obj
+      if (returnedId !== id) return
+      window.removeEventListener("message", handler)
+      if (error) return reject(error.href ? error : new Error(error))
+      resolve(response)
+    }
+
+    const win = frame ? frame.contentWindow : window.top
+    window.addEventListener("message", handler)
+    win.postMessage(message, "*")
+  })
+
+const on = (type, fn) => {
+  window.addEventListener("message", event => {
+    let obj = event.data
+    try {
+      if (typeof obj === "string") obj = JSON.parse(event.data)
+    } catch (e) {
+      return
+    }
+
+    const reply = o => {
+      event.source.postMessage(
+        JSON.stringify(Object.assign(o, { id: obj.id })),
+        "*"
+      )
+    }
+
+    if (obj.type === type) {
+      Promise.resolve(fn(obj.payload))
+        .then(response => reply({ response }))
+        .catch(error => {
+          console.error(error)
+          reply({
+            error: error.stack || error.message
+          })
+        })
+      return true
+    }
+  })
+}
+
+const checkUrl = src =>
+  new Promise(resolve => {
+    const workerBody =
+      "data:application/javascript," +
+      encodeURIComponent(`
+function reply(ok){
+  self.postMessage(JSON.stringify({ok: ok}));
+}
+
+try {
+  importScripts("${src}");
+  reply(true);
+} catch(e) {
+  reply(!(e instanceof DOMException));
+}
+`)
+
+    const worker = new Worker(workerBody)
+
+    const timeout = setTimeout(() => {
+      resolve(false)
+      worker.terminate()
+    }, 3000)
+
+    worker.onmessage = e => {
+      const { ok } = JSON.parse(e.data)
+      resolve(ok)
+      worker.terminate()
+      clearTimeout(timeout)
+    }
+  })
+
+const checkUrlWithIframe = src =>
+  new Promise(r => {
+    const body = `data:text/html,${encodeURIComponent(
+      `<script>
+var on = ${on.toString()};
+var checkUrl = ${checkUrl.toString()};
+on('checkUrl', checkUrl);
+</script>`
+    )}`
+
+    const iframe = document.createElement("iframe")
+
+    iframe.setAttribute("sandbox", "allow-scripts")
+    iframe.setAttribute("hidden", "true")
+    iframe.setAttribute("src", body)
+    document.body.appendChild(iframe)
+
+    iframe.onload = () => {
+      send("checkUrl", src, iframe).then(result => {
+        r(result)
+        document.body.removeChild(iframe)
+      })
+    }
+  })
+
+const debouncedFetch = (() => {
+  let timeout = null
+
+  return href =>
+    new Promise((resolve, reject) => {
+      clearTimeout(timeout)
+      timeout = setTimeout(() => {
+        checkUrlWithIframe(href)
+          .then(resolve)
+          .catch(reject)
+      }, 500)
+    })
+})()
+
+export default {
+  test: function(elem) {
+    return new Promise((resolve, reject) => {
+      if (elem.tagName !== "A") return resolve(true)
+      const href = elem.getAttribute("href")
+
+      // If url is invalid
+      if (!isValidURL(href)) return resolve(false)
+
+      debouncedFetch(href).then(resolve)
+    })
+  },
+
+  data: elem => {
+    return {
+      href: elem.getAttribute("href")
+    }
+  },
+
+  form: () => [
+    {
+      label: formatMessage("Ensure this link is correct."),
+      dataKey: "href",
+      disabledIf: data => data.ignore
+    },
+    {
+      label: formatMessage("Ignore this link in the future."),
+      checkbox: true,
+      dataKey: "ignore"
+    }
+  ],
+
+  update: function(elem, data) {
+    const rootElem = elem.parentNode
+
+    if (data.ignore) {
+      elem.setAttribute("data-ignore-a11y-check", "true")
+    }
+
+    if (data.href !== elem.getAttribute("href")) {
+      elem.setAttribute("href", data.href)
+    }
+
+    return elem
+  },
+
+  rootNode: function(elem) {
+    return elem.parentNode
+  },
+
+  // Note, these messages are poor and should be replaced with
+  // better text.
+  message: () => formatMessage("This link could not be verified."),
+
+  why: () => formatMessage("Links should not be broken."),
+
+  link: " --- fill in --- "
+}