diff --git a/url/toascii.json b/url/toascii.json
new file mode 100644
index 00000000000000..814f06e794866d
--- /dev/null
+++ b/url/toascii.json
@@ -0,0 +1,149 @@
+[
+  "This resource is focused on highlighting issues with UTS #46 ToASCII",
+  {
+    "comment": "Label with hyphens in 3rd and 4th position",
+    "input": "aa--",
+    "output": "aa--"
+  },
+  {
+    "input": "a†--",
+    "output": "xn--a---kp0a"
+  },
+  {
+    "input": "ab--c",
+    "output": "ab--c"
+  },
+  {
+    "comment": "Label with leading hyphen",
+    "input": "-x",
+    "output": "-x"
+  },
+  {
+    "input": "-†",
+    "output": "xn----xhn"
+  },
+  {
+    "input": "-x.xn--nxa",
+    "output": "-x.xn--nxa"
+  },
+  {
+    "input": "-x.β",
+    "output": "-x.xn--nxa"
+  },
+  {
+    "comment": "Label with trailing hyphen",
+    "input": "x-.xn--nxa",
+    "output": "x-.xn--nxa"
+  },
+  {
+    "input": "x-.β",
+    "output": "x-.xn--nxa"
+  },
+  {
+    "comment": "Empty labels",
+    "input": "x..xn--nxa",
+    "output": "x..xn--nxa"
+  },
+  {
+    "input": "x..β",
+    "output": "x..xn--nxa"
+  },
+  {
+    "comment": "Invalid Punycode",
+    "input": "xn--a",
+    "output": null
+  },
+  {
+    "input": "xn--a.xn--nxa",
+    "output": null
+  },
+  {
+    "input": "xn--a.β",
+    "output": null
+  },
+  {
+    "comment": "Valid Punycode",
+    "input": "xn--nxa.xn--nxa",
+    "output": "xn--nxa.xn--nxa"
+  },
+  {
+    "comment": "Mixed",
+    "input": "xn--nxa.β",
+    "output": "xn--nxa.xn--nxa"
+  },
+  {
+    "input": "ab--c.xn--nxa",
+    "output": "ab--c.xn--nxa"
+  },
+  {
+    "input": "ab--c.β",
+    "output": "ab--c.xn--nxa"
+  },
+  {
+    "comment": "CheckJoiners is true",
+    "input": "\u200D.example",
+    "output": null
+  },
+  {
+    "input": "xn--1ug.example",
+    "output": null
+  },
+  {
+    "comment": "CheckBidi is true",
+    "input": "يa",
+    "output": null
+  },
+  {
+    "input": "xn--a-yoc",
+    "output": null
+  },
+  {
+    "comment": "processing_option is Nontransitional_Processing",
+    "input": "ශ්‍රී",
+    "output": "xn--10cl1a0b660p"
+  },
+  {
+    "input": "نامه‌ای",
+    "output": "xn--mgba3gch31f060k"
+  },
+  {
+    "comment": "U+FFFD",
+    "input": "\uFFFD.com",
+    "output": null
+  },
+  {
+    "comment": "U+FFFD character encoded in Punycode",
+    "input": "xn--zn7c.com",
+    "output": null
+  },
+  {
+    "comment": "Label longer than 63 code points",
+    "input": "x01234567890123456789012345678901234567890123456789012345678901x",
+    "output": "x01234567890123456789012345678901234567890123456789012345678901x"
+  },
+  {
+    "input": "x01234567890123456789012345678901234567890123456789012345678901†",
+    "output": "xn--x01234567890123456789012345678901234567890123456789012345678901-6963b"
+  },
+  {
+    "input": "x01234567890123456789012345678901234567890123456789012345678901x.xn--nxa",
+    "output": "x01234567890123456789012345678901234567890123456789012345678901x.xn--nxa"
+  },
+  {
+    "input": "x01234567890123456789012345678901234567890123456789012345678901x.β",
+    "output": "x01234567890123456789012345678901234567890123456789012345678901x.xn--nxa"
+  },
+  {
+    "comment": "Domain excluding TLD longer than 253 code points",
+    "input": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.x",
+    "output": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.x"
+  },
+  {
+    "input": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.xn--nxa",
+    "output": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.xn--nxa"
+  },
+  {
+    "input": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.β",
+    "output": "01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.01234567890123456789012345678901234567890123456789.0123456789012345678901234567890123456789012345678.xn--nxa"
+  }
+]
diff --git a/url/toascii.window.js b/url/toascii.window.js
new file mode 100644
index 00000000000000..b49ef20b7713ec
--- /dev/null
+++ b/url/toascii.window.js
@@ -0,0 +1,62 @@
+async_test(t => {
+  const request = new XMLHttpRequest()
+  request.open("GET", "toascii.json")
+  request.send()
+  request.responseType = "json"
+  request.onload = t.step_func_done(() => {
+    runTests(request.response)
+  })
+}, "Loading data…")
+
+function makeURL(type, input) {
+  input = "https://" + input + "/x"
+  if(type === "url") {
+    return new URL(input)
+  } else {
+    const url = document.createElement(type)
+    url.href = input
+    return url
+  }
+}
+
+function runTests(tests) {
+  for(var i = 0, l = tests.length; i < l; i++) {
+    let hostTest = tests[i]
+    if (typeof hostTest === "string") {
+      continue // skip comments
+    }
+    const typeName = { "url": "URL", "a": "<a>", "area": "<area>" }
+    ;["url", "a", "area"].forEach((type) => {
+      test(() => {
+        if(hostTest.output !== null) {
+          const url = makeURL("url", hostTest.input)
+          assert_equals(url.host, hostTest.output)
+          assert_equals(url.hostname, hostTest.output)
+          assert_equals(url.pathname, "/x")
+          assert_equals(url.href, "https://" + hostTest.output + "/x")
+        } else {
+          if(type === "url") {
+            assert_throws(new TypeError, () => makeURL("url", hostTest.input))
+          } else {
+            const url = makeURL(type, hostTest.input)
+            assert_equals(url.host, "")
+            assert_equals(url.hostname, "")
+            assert_equals(url.pathname, "")
+            assert_equals(url.href, "https://" + hostTest.input + "/x")
+          }
+        }
+      }, hostTest.input + " (using " + typeName[type] + ")")
+      ;["host", "hostname"].forEach((val) => {
+        test(() => {
+          const url = makeURL(type, "x")
+          url[val] = hostTest.input
+          if(hostTest.output !== null) {
+            assert_equals(url[val], hostTest.output)
+          } else {
+            assert_equals(url[val], "x")
+          }
+        }, hostTest.input + " (using " + typeName[type] + "." + val + ")")
+      })
+    })
+  }
+}