diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7363-json-stringify-live-capsules.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7363-json-stringify-live-capsules.ts.json
new file mode 100644
index 000000000..580e84ff0
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7363-json-stringify-live-capsules.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/7363-json-stringify-live-capsules.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/runtime/src/scr_json.c b/packages/runtime/src/scr_json.c
index cf658313f..dfa81ace6 100644
--- a/packages/runtime/src/scr_json.c
+++ b/packages/runtime/src/scr_json.c
@@ -10744,8 +10744,9 @@ static bool scr_json_callback_depth(size_t depth) {
 
 static ScrStr *scr_json_index_key(size_t index) {
   char bytes[32];
-  int length = snprintf(bytes, sizeof bytes, "%zu", index);
-  return scr_str_new(bytes, (size_t)length);
+  /* array indexes are below 2^32: exact doubles, printed as integers */
+  size_t length = scr_f64_to_str((double)index, bytes);
+  return scr_str_new(bytes, length);
 }
 
 /* Keys passed here come from our own index formatter or own-key walk. */
@@ -11021,12 +11022,22 @@ static bool scr_json_live_container(const ScrDyn *value, bool inspect) {
  * { type, data } view, and an object with a callable toJSON through that
  * method, called with the key. Returns the value to serialize (+1), or NULL
  * with an exception pending. */
-static ScrDyn *scr_json_to_json(ScrDyn *value, const ScrStr *key) {
+/* The toJSON key argument: `key`, or the decimal spelling of array index
+ * `index` when `key` is NULL (formed only for a call that receives it). */
+static ScrDyn *scr_json_key_arg(const ScrStr *key, size_t index) {
+  if (key) return scr_dyn_new_str((ScrStr *)key);
+  ScrStr *text = scr_json_index_key(index);
+  ScrDyn *name = scr_dyn_new_str(text);
+  scr_str_release(text);
+  return name;
+}
+
+static ScrDyn *scr_json_to_json_at(ScrDyn *value, const ScrStr *key, size_t index) {
   /* An instance of a class declared `extends Date` converts through its
    * toJSON, declared or inherited. */
   double time;
   if (value->kind == SCR_DYN_TYPED_REF && scr_dyn_date_class_time(value, &time)) {
-    ScrDyn *name = scr_dyn_new_str((ScrStr *)key);
+    ScrDyn *name = scr_json_key_arg(key, index);
     ScrDyn *converted = scr_dyn_date_class_to_json(value, name);
     scr_dyn_release(name);
     scr_dyn_release(value);
@@ -11054,7 +11065,7 @@ static ScrDyn *scr_json_to_json(ScrDyn *value, const ScrStr *key) {
     ScrDyn *method = scr_dyn_obj_read(inspected, "toJSON", 6);
     if (!method) { scr_dyn_release(view); scr_dyn_release(value); return NULL; }
     if (method->kind == SCR_DYN_FUNC) {
-      ScrDyn *name = scr_dyn_new_str((ScrStr *)key);
+      ScrDyn *name = scr_json_key_arg(key, index);
       ScrDyn *args[] = { name };
       scr_dyn_this_push_dyn(value);
       ScrDyn *converted = scr_dyn_call(method, args, 1, "toJSON");
@@ -11069,6 +11080,10 @@ static ScrDyn *scr_json_to_json(ScrDyn *value, const ScrStr *key) {
   return value;
 }
 
+static ScrDyn *scr_json_to_json(ScrDyn *value, const ScrStr *key) {
+  return scr_json_to_json_at(value, key, 0);
+}
+
 static ScrDyn *scr_json_replace(const ScrDyn *holder, const ScrStr *key, const ScrDyn *replacer) {
   ScrDyn *value = scr_json_member(holder, key);
   if (!value) return NULL;
@@ -11203,6 +11218,81 @@ static ScrDyn *scr_json_property_list(const ScrDyn *replacer) {
   return list;
 }
 
+/* The protocol walk over a live record or array capsule without a replacer
+ * (the caller entered it on the circular-structure stack). Members are read
+ * from the native value exactly as scr_json_member reads them, but the walk
+ * needs no key list: a record's present fields are snapshotted by index (its
+ * keys are the immortal field names) and an array's indexes are counted, so
+ * an index key string is formed only for a toJSON call that receives it. */
+static bool scr_json_live_write(ScrJsonBuf *buffer, const ScrDyn *value, bool array,
+                                const ScrStr *gap, size_t depth) {
+  const ScrDynTypedRecordOps *record = array ? NULL : scr_typed_ref_record_ops(value);
+  /* EnumerableOwnProperties runs once, before any member's toJSON (the
+   * caller sends records of more than 64 fields down the key-list walk). */
+  uint64_t present = 0;
+  size_t length;
+  if (array) {
+    length = ((ScrArr *)value->v.typed_ref.ptr)->len;
+  } else {
+    length = record->count;
+    for (size_t i = 0; i < length; i++)
+      if (record->fixed || record->has(value->v.typed_ref.ptr, i)) present |= (uint64_t)1 << i;
+  }
+  scr_jb_putc(buffer, array ? '[' : '{');
+  bool first = true;
+  for (size_t i = 0; i < length; i++) {
+    if (!array && !(present & ((uint64_t)1 << i))) continue;
+    const ScrStr *key = array ? NULL : record->names[i];
+    ScrDyn *child;
+    if (array) {
+      scr_jb_edge_idx(buffer, i);
+      /* scr_json_member's index read, minus the key: a present element
+       * answers directly; holes, a length a callback shrank, a capsule a
+       * callback materialized and inherited event members take the keyed
+       * read */
+      child = !scr_event_ref_hooks && scr_dyn_typed_ref_array_ops(value) ? scr_dyn_typed_ref_element(value, i)
+                                                                        : NULL;
+      if (!child) {
+        ScrStr *index = scr_json_index_key(i);
+        child = scr_json_member(value, index);
+        scr_str_release(index);
+      }
+    } else {
+      scr_jb_edge_key(buffer, key);
+      child = scr_json_member(value, key);
+    }
+    if (child) child = scr_json_to_json_at(child, key, i);
+    if (!child) return false;
+    if (!array && scr_json_omitted(child)) {
+      scr_dyn_release(child);
+      continue;
+    }
+    if (!first) scr_jb_putc(buffer, ',');
+    first = false;
+    scr_json_gap(buffer, gap, depth + 1);
+    if (!array) {
+      scr_jb_put_json_str(buffer, key);
+      scr_jb_putc(buffer, ':');
+      if (gap->len) scr_jb_putc(buffer, ' ');
+    }
+    bool ok = true;
+    if (scr_json_omitted(child)) scr_jb_puts(buffer, "null");
+    else if (scr_json_plain_value(child)) {
+      /* the protocol walk's depth check, then the primitive itself */
+      ok = scr_json_callback_depth(depth + 1);
+      if (ok) {
+        scr_dyn_json_write(buffer, child);
+        ok = !scr_exc_pending();
+      }
+    } else ok = scr_json_replaced_write(buffer, child, scr_dyn_undefined(), NULL, gap, depth + 1);
+    scr_dyn_release(child);
+    if (!ok) return false;
+  }
+  if (!first) scr_json_gap(buffer, gap, depth);
+  scr_jb_putc(buffer, array ? ']' : '}');
+  return true;
+}
+
 /* `properties`, when present, is an array replacer's PropertyList: objects
  * serialize exactly those keys, own or inherited, in that order; arrays
  * keep all their indexes. */
@@ -11232,6 +11322,12 @@ static bool scr_json_replaced_write(ScrJsonBuf *buffer, const ScrDyn *value,
    * after the current frame leaves the traversal stack. */
   const void *identity = view || live ? value->v.typed_ref.ptr : (const void *)value;
   if (!scr_jb_enter(buffer, identity, array)) { scr_dyn_release(view); return false; }
+  if (live && replacer->kind == SCR_DYN_UNDEF && !properties &&
+      (array || scr_typed_ref_record_ops(value)->count <= 64)) {
+    bool ok = scr_json_live_write(buffer, value, array, gap, depth);
+    scr_jb_leave(buffer);
+    return ok;
+  }
   scr_jb_putc(buffer, array ? '[' : '{');
   ScrDyn *keys = array ? NULL : properties ? scr_dyn_retain((ScrDyn *)properties) : scr_dyn_obj_keys(observed);
   if (scr_exc_pending()) { scr_dyn_release(keys); scr_dyn_release(view); scr_jb_leave(buffer); return false; }
diff --git a/tests/corpus/7363-json-stringify-live-capsules.ts b/tests/corpus/7363-json-stringify-live-capsules.ts
new file mode 100644
index 000000000..5522ede5f
--- /dev/null
+++ b/tests/corpus/7363-json-stringify-live-capsules.ts
@@ -0,0 +1,73 @@
+// JSON.stringify of typed records and arrays reached through `unknown`:
+// members are read from the native values in key order, toJSON receives the
+// member key (an index string inside arrays), undefined members drop out of
+// objects and become null in arrays, and the key list is fixed before any
+// toJSON runs.
+interface Product {
+  id: string;
+  name: string;
+  priceCents: number;
+  tags: string[];
+  note?: string;
+}
+
+function stringify(value: unknown, space?: number): string {
+  return JSON.stringify(value, undefined, space);
+}
+
+const products: Product[] = [
+  { id: "p1", name: "Keyboard", priceCents: 12900, tags: ["hardware", "input"] },
+  { id: "p2", name: "Quote \"and\" slash \\", priceCents: 0.5, tags: [], note: "café ☕" },
+];
+console.log(stringify({ products, count: products.length }));
+console.log(stringify(products, 2));
+const second: Product = products[1]!;
+delete second.note;
+console.log(stringify(second));
+
+class Money {
+  cents: number;
+  constructor(cents: number) {
+    this.cents = cents;
+  }
+  toJSON(key: string): string {
+    return `${key}:${(this.cents / 100).toFixed(2)}`;
+  }
+}
+const prices: Money[] = [new Money(100), new Money(2550)];
+console.log(stringify(prices), stringify({ total: new Money(5) }));
+
+const numbers: number[] = [1, -0, NaN, Infinity, 2.5, 1e21];
+console.log(stringify(numbers));
+const maybe: (string | undefined)[] = ["a", undefined, "c"];
+console.log(stringify(maybe), stringify({ maybe }));
+const nested: number[][] = [[1, 2], [], [3]];
+console.log(stringify(nested, 1));
+
+// a toJSON that deletes a later optional field: the field was present when
+// the key list was taken, so its (now undefined) value is dropped
+interface Order {
+  first: { toJSON(): string };
+  note?: string;
+}
+const order: Order = { first: { toJSON: () => "x" }, note: "kept?" };
+order.first = {
+  toJSON: () => {
+    delete order.note;
+    return "first";
+  },
+};
+console.log(stringify(order));
+
+// circular structures through capsules report the path
+interface Node {
+  name: string;
+  children: Node[];
+}
+const root: Node = { name: "root", children: [] };
+root.children.push({ name: "leaf", children: [root] });
+try {
+  stringify(root);
+} catch (error) {
+  console.log((error as Error).message);
+}
diff --git a/tests/harness/corpus-costs/7363-json-stringify-live-capsules.ts.json b/tests/harness/corpus-costs/7363-json-stringify-live-capsules.ts.json
new file mode 100644
index 000000000..27b641ffe
--- /dev/null
+++ b/tests/harness/corpus-costs/7363-json-stringify-live-capsules.ts.json
@@ -0,0 +1 @@
+{ "plain": 2900, "san": 3200 }