diff --git a/src/domain/browserObservation.test.ts b/src/domain/browserObservation.test.ts
index ddf03ddad6..6df175f653 100644
--- a/src/domain/browserObservation.test.ts
+++ b/src/domain/browserObservation.test.ts
@@ -11,6 +11,32 @@ import {
 } from "./browserObservation.js";
 
 describe("browser observation contracts", () => {
+  it.each(["127.0.0.1", "[::1]"])(
+    "preserves explicitly supplied default endpoint ports on %s",
+    (host) => {
+      const http = `http://${host}:80`;
+      expect(browserEndpointSchema.parse(http)).toBe(http);
+      expect(
+        browserEndpointSchema.parse(browserEndpointSchema.parse(http)),
+      ).toBe(http);
+      expect(recordedBrowserObservationEndpointSchema.parse(http)).toBe(http);
+      const socket = `ws://${host}:80/devtools/browser/id`;
+      expect(browserObservationEndpointSchema.parse(socket)).toEqual({
+        transport: "browser_websocket",
+        url: socket,
+        recorded: `ws://${host}:80/devtools/browser/[REDACTED]`,
+      });
+      for (const value of [
+        `http://${host}`,
+        `ws://${host}/devtools/browser/id`,
+        "http://192.0.2.1:80",
+      ])
+        expect(
+          browserObservationEndpointSchema.safeParse(value).success,
+          value,
+        ).toBe(false);
+    },
+  );
   it("normalizes exact HTTP origins without accepting broader URL scopes", () => {
     expect(browserOriginSchema.parse("https://Example.COM:443")).toBe(
       "https://example.com",
diff --git a/src/domain/browserObservation.ts b/src/domain/browserObservation.ts
index 691b68c70a..94f6ee2931 100644
--- a/src/domain/browserObservation.ts
+++ b/src/domain/browserObservation.ts
@@ -65,31 +65,45 @@ const HTTP_ENDPOINT_MESSAGE =
 const BROWSER_SOCKET_PATH = "/devtools/browser/";
 const REDACTED_BROWSER_SOCKET_PATH = `${BROWSER_SOCKET_PATH}[REDACTED]`;
 
-/** Normalized origin of an accepted loopback CDP HTTP discovery endpoint. */
-const httpDiscoveryOrigin = (url: URL): string | undefined =>
+/** Retain an explicit default port, which URL.port and URL.origin erase. */
+const explicitEndpointAuthority = (
+  value: string,
+  url: URL,
+): string | undefined => {
+  const authority = /^[a-z][a-z0-9+.-]*:\/\/([^/?#\\]*)/iu.exec(value)?.[1];
+  const port =
+    authority === undefined ? undefined : /:([0-9]+)$/u.exec(authority)?.[1];
+  return port === undefined
+    ? undefined
+    : `${url.protocol}//${url.hostname}:${String(Number(port))}`;
+};
+
+/** Normalized explicit-port origin of a loopback CDP HTTP discovery endpoint. */
+const httpDiscoveryOrigin = (value: string, url: URL): string | undefined =>
   url.protocol === "http:" &&
   isLiteralLoopbackHostname(url.hostname) &&
-  url.port !== "" &&
   url.username === "" &&
   url.password === "" &&
   url.pathname === "/" &&
   !urlDeclaresQueryOrFragment(url)
-    ? url.origin
+    ? explicitEndpointAuthority(value, url)
     : undefined;
 
 /** Scheme and authority of an accepted loopback CDP browser WebSocket. */
-const browserSocketAuthority = (url: URL): string | undefined => {
+const browserSocketAuthority = (
+  value: string,
+  url: URL,
+): string | undefined => {
   const id = url.pathname.slice(BROWSER_SOCKET_PATH.length);
   return url.protocol === "ws:" &&
     isLiteralLoopbackHostname(url.hostname) &&
-    url.port !== "" &&
     url.username === "" &&
     url.password === "" &&
     !urlDeclaresQueryOrFragment(url) &&
     url.pathname.startsWith(BROWSER_SOCKET_PATH) &&
     id.length > 0 &&
     !id.includes("/")
-    ? `${url.protocol}//${url.host}`
+    ? explicitEndpointAuthority(value, url)
     : undefined;
 };
 
@@ -99,7 +113,7 @@ export const browserEndpointSchema = z
   .min(1)
   .transform((value, context) => {
     const url = URL.parse(value);
-    const origin = url === null ? undefined : httpDiscoveryOrigin(url);
+    const origin = url === null ? undefined : httpDiscoveryOrigin(value, url);
     if (origin !== undefined) return origin;
     context.addIssue({
       code: "custom",
@@ -132,14 +146,14 @@ export const browserObservationEndpointSchema = z
       context.addIssue({ code: "custom", message: "Invalid CDP endpoint URL" });
       return z.NEVER;
     }
-    const origin = httpDiscoveryOrigin(url);
+    const origin = httpDiscoveryOrigin(value, url);
     if (origin !== undefined)
       return { transport: "http_discovery", url: origin, recorded: origin };
-    const authority = browserSocketAuthority(url);
+    const authority = browserSocketAuthority(value, url);
     if (authority !== undefined)
       return {
         transport: "browser_websocket",
-        url: url.href,
+        url: `${authority}${url.pathname}`,
         recorded: `${authority}${REDACTED_BROWSER_SOCKET_PATH}`,
       };
     context.addIssue({
@@ -161,8 +175,8 @@ export const recordedBrowserObservationEndpointSchema = z
       const url = URL.parse(value);
       return (
         url !== null &&
-        (httpDiscoveryOrigin(url) !== undefined ||
-          (browserSocketAuthority(url) !== undefined &&
+        (httpDiscoveryOrigin(value, url) !== undefined ||
+          (browserSocketAuthority(value, url) !== undefined &&
             url.pathname === REDACTED_BROWSER_SOCKET_PATH))
       );
     },