diff --git a/src/cli.ts b/src/cli.ts
index b20cb93..31628de 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -233,9 +233,10 @@ const HELP = `
   has replaced by the partial run's, and its other shots added. Both must compare the same origins.
 
   renderdiff probe loads one URL --loads times (default 8, in parallel up to --concurrency),
-  each in a fresh browser context as a run loads a side, and lists the elements whose computed
-  style or position in their parent varies between loads: what to mask. Exits 0 if nothing
-  varies, 1 if something does, 3 if a load errored.
+  each in a fresh browser context as a run loads a side (with the storage state of the config
+  side the URL is on), and lists the elements whose computed style or position in their parent
+  varies between loads: what to mask. Exits 0 if nothing varies, 1 if something does, 3 if a
+  load errored.
 
   Writes report.html, results.json and crops of each change to --out. Exits 1 if any
   shot differs and isn't accepted (with --threshold, only if one scores below it;
@@ -496,13 +497,25 @@ function only(values: string[], routes: Route[]): Route[] {
   return routes.filter((r) => picked.has(r));
 }
 
+const PROBE_FLAGS = [
+  "--help",
+  "--version",
+  "--left",
+  "--config",
+  "--width",
+  "--concurrency",
+  "--mask",
+  "--hide",
+  "--mask-media",
+  "--no-freeze-video",
+  "--storage-state",
+];
+
 /** `renderdiff probe <url>`: load one URL several times and list what varies between loads. */
 async function probe(a: Args, loads: number): Promise<never> {
   if (!a.left) die("probe needs a URL: renderdiff probe <url>");
   if (a.right || a.routes.length) die("probe takes one URL, with its path");
   if ((a.widths?.length ?? 0) > 1) die("probe takes one --width");
-  if (a.selector) die("probe does not take --selector; it walks the whole page");
-  if (a.only) die("probe does not take --only");
   if (!isHttpUrl(a.left)) die(`not an http(s) URL: ${a.left}`);
   const u = new URL(a.left);
   let route: Route;
@@ -517,7 +530,24 @@ async function probe(a: Args, loads: number): Promise<never> {
   } catch (e) {
     die(e instanceof Error ? e.message : String(e));
   }
+  const at = (o?: string) => !!o && isHttpUrl(o) && new URL(o).origin === u.origin;
+  const side = at(fileConfig.right)
+    ? "right"
+    : at(fileConfig.left)
+      ? "left"
+      : cfg.storageState.right
+        ? "right"
+        : "left";
+  const s = cfg.storageState[side];
+  cfg.storageState = { left: s, right: s };
   if (configPath) console.log(`Config: ${configPath}`);
+  if (s) console.log(`Storage state: ${s} (${side})`);
+  if (!a.widths) {
+    const more = cfg.widths.length > 1;
+    console.log(
+      `Width: ${cfg.widths[0]}${more ? ` (first of ${cfg.widths.join(", ")}; --width <n> for another)` : ""}`,
+    );
+  }
   await preflight(cfg.left, cfg.left);
   const { probe } = await import("./probe.ts");
   try {
@@ -538,6 +568,10 @@ try {
   const argv = process.argv.slice(probing ? 3 : 2);
   if (probing) loads = takeLoads(argv);
   args = parseArgs(argv);
+  const extra =
+    probing &&
+    argv.map((t) => t.split("=")[0]!).find((f) => f.startsWith("--") && !PROBE_FLAGS.includes(f));
+  if (extra) throw new Error(`probe does not take ${extra}`);
 } catch (e) {
   die(e instanceof Error ? e.message : String(e));
 }
diff --git a/tests/unit/cli-args.test.ts b/tests/unit/cli-args.test.ts
index ee6da45..d4aba70 100644
--- a/tests/unit/cli-args.test.ts
+++ b/tests/unit/cli-args.test.ts
@@ -527,6 +527,50 @@ describe("probe", () => {
     await rejects(["probe", U, "--width", "1440", "--width", "375"], "probe takes one --width");
     await rejects(["probe", U, "--selector", "main"], "probe does not take --selector");
   });
+
+  test("refuses flags it would ignore", async () => {
+    await rejects(["probe", U, "--dry-run"], "probe does not take --dry-run");
+    await rejects(["probe", U, "--out=x"], "probe does not take --out");
+    await rejects(
+      ["probe", U, "--left-storage-state", "s.json"],
+      "probe does not take --left-storage-state",
+    );
+  });
+
+  test("names the width it falls back to", async () => {
+    const r = await runCli(["probe", "http://127.0.0.1:1/a"], { noOut: true });
+    assert.equal(r.code, 2, r.stderr);
+    assert.match(
+      r.stdout,
+      /Width: 1440 \(first of 1440, 1152, 896, 704, 375; --width <n> for another\)/,
+    );
+    const w = await runCli(["probe", "http://127.0.0.1:1/a", "--width", "375"], { noOut: true });
+    assert.equal(w.code, 2, w.stderr);
+    assert.doesNotMatch(w.stdout, /Width:/);
+  });
+
+  test("uses the storage state of the side the URL is on, else the configured one", async () => {
+    const project = (storageState: string) => {
+      const cwd = tempDir();
+      fs.writeFileSync(
+        path.join(cwd, "renderdiff.config.mjs"),
+        `export default { left: "http://127.0.0.1:1", right: "http://127.0.0.1:2", storageState: ${storageState} };`,
+      );
+      for (const f of ["l.json", "r.json"]) fs.writeFileSync(path.join(cwd, f), "{}");
+      return cwd;
+    };
+    const state = async (cwd: string, url: string) => {
+      const r = await runCli(["probe", url], { cwd, noOut: true });
+      assert.match(r.stderr, /not responding/);
+      return r.stdout;
+    };
+    const both = project(`{ left: "l.json", right: "r.json" }`);
+    assert.match(await state(both, "http://127.0.0.1:1/a"), /Storage state: .*l\.json \(left\)$/m);
+    assert.match(await state(both, "http://127.0.0.1:2/a"), /Storage state: .*r\.json \(right\)$/m);
+    assert.match(await state(both, "http://127.0.0.1:3/a"), /Storage state: .*r\.json \(right\)$/m);
+    const left = project(`{ left: "l.json" }`);
+    assert.match(await state(left, "http://127.0.0.1:3/a"), /Storage state: .*l\.json \(left\)$/m);
+  });
 });
 
 describe("preflight", () => {