diff --git a/templates/node/src/client.ts.twig b/templates/node/src/client.ts.twig
index 5ed9b8b31e..8ed155e5ec 100644
--- a/templates/node/src/client.ts.twig
+++ b/templates/node/src/client.ts.twig
@@ -85,6 +85,15 @@ function fillDefaults(
             result[key] = fillDefaults(result[key], child, models);
         }
     }
+    // The spread drops the non-enumerable JSON toString that Client.call attaches.
+    if (Object.prototype.hasOwnProperty.call(value, 'toString')) {
+        Object.defineProperty(result, 'toString', {
+            value: () => JSONbig.stringify(result),
+            writable: true,
+            enumerable: false,
+            configurable: true,
+        });
+    }
     return result;
 }
 
diff --git a/templates/react-native/src/client.ts.twig b/templates/react-native/src/client.ts.twig
index 65ec4b2e4e..5d7021fa25 100644
--- a/templates/react-native/src/client.ts.twig
+++ b/templates/react-native/src/client.ts.twig
@@ -86,6 +86,15 @@ function fillDefaults(
             result[key] = fillDefaults(result[key], child, models);
         }
     }
+    // The spread drops the non-enumerable JSON toString that Client.call attaches.
+    if (Object.prototype.hasOwnProperty.call(value, 'toString')) {
+        Object.defineProperty(result, 'toString', {
+            value: () => JSONbig.stringify(result),
+            writable: true,
+            enumerable: false,
+            configurable: true,
+        });
+    }
     return result;
 }
 
diff --git a/templates/web/src/client.ts.twig b/templates/web/src/client.ts.twig
index 554eb54c36..4deb9bf64f 100644
--- a/templates/web/src/client.ts.twig
+++ b/templates/web/src/client.ts.twig
@@ -86,6 +86,15 @@ function fillDefaults(
             result[key] = fillDefaults(result[key], child, models);
         }
     }
+    // The spread drops the non-enumerable JSON toString that Client.call attaches.
+    if (Object.prototype.hasOwnProperty.call(value, 'toString')) {
+        Object.defineProperty(result, 'toString', {
+            value: () => JSONbig.stringify(result),
+            writable: true,
+            enumerable: false,
+            configurable: true,
+        });
+    }
     return result;
 }
 
diff --git a/tests/e2e/Base.php b/tests/e2e/Base.php
index b9dcd38539..4a356102ca 100644
--- a/tests/e2e/Base.php
+++ b/tests/e2e/Base.php
@@ -96,6 +96,10 @@ abstract class Base extends TestCase
         'preset: name=server, count=25, enabled=true',
     ];
 
+    protected const JS_MODEL_TO_STRING_RESPONSES = [
+        'preset toString: {"name":"guest","count":25,"enabled":false,"tier":"free"}',
+    ];
+
     protected const PYTHON_MODEL_DEFAULT_RESPONSES = [
         'preset tier: PresetTier.FREE',
     ];
diff --git a/tests/e2e/Node18Test.php b/tests/e2e/Node18Test.php
index ae3b286702..6f491dc346 100644
--- a/tests/e2e/Node18Test.php
+++ b/tests/e2e/Node18Test.php
@@ -58,6 +58,7 @@ final class Node18Test extends Base
         ...Base::MODEL_RESPONSES,
         ...Base::OPTIONAL_PARAM_RESPONSES,
         ...Base::MODEL_DEFAULT_RESPONSES,
+        ...Base::JS_MODEL_TO_STRING_RESPONSES,
         ...Base::EXCEPTION_RESPONSES,
         ...Base::OAUTH_RESPONSES,
         ...Base::QUERY_HELPER_RESPONSES,
diff --git a/tests/e2e/Node20Test.php b/tests/e2e/Node20Test.php
index 19f12194c4..4bc796c382 100644
--- a/tests/e2e/Node20Test.php
+++ b/tests/e2e/Node20Test.php
@@ -58,6 +58,7 @@ final class Node20Test extends Base
         ...Base::MODEL_RESPONSES,
         ...Base::OPTIONAL_PARAM_RESPONSES,
         ...Base::MODEL_DEFAULT_RESPONSES,
+        ...Base::JS_MODEL_TO_STRING_RESPONSES,
         ...Base::EXCEPTION_RESPONSES,
         ...Base::OAUTH_RESPONSES,
         ...Base::QUERY_HELPER_RESPONSES,
diff --git a/tests/e2e/Node26Test.php b/tests/e2e/Node26Test.php
index c6a14b9d9b..c7bb895da7 100644
--- a/tests/e2e/Node26Test.php
+++ b/tests/e2e/Node26Test.php
@@ -58,6 +58,7 @@ final class Node26Test extends Base
         ...Base::MODEL_RESPONSES,
         ...Base::OPTIONAL_PARAM_RESPONSES,
         ...Base::MODEL_DEFAULT_RESPONSES,
+        ...Base::JS_MODEL_TO_STRING_RESPONSES,
         ...Base::EXCEPTION_RESPONSES,
         ...Base::OAUTH_RESPONSES,
         ...Base::QUERY_HELPER_RESPONSES,
diff --git a/tests/e2e/ReactNativeTest.php b/tests/e2e/ReactNativeTest.php
index b6c9b4adb7..5faf16cd79 100644
--- a/tests/e2e/ReactNativeTest.php
+++ b/tests/e2e/ReactNativeTest.php
@@ -63,6 +63,7 @@ final class ReactNativeTest extends Base
         ...Base::MODEL_RESPONSES,
         ...Base::OPTIONAL_PARAM_RESPONSES,
         ...Base::MODEL_DEFAULT_RESPONSES,
+        ...Base::JS_MODEL_TO_STRING_RESPONSES,
         ...Base::EXCEPTION_RESPONSES,
         ...Base::REALTIME_RESPONSES,
         ...Base::QUERY_HELPER_RESPONSES,
diff --git a/tests/e2e/WebChromiumTest.php b/tests/e2e/WebChromiumTest.php
index ccf0683f3f..4233789dd7 100644
--- a/tests/e2e/WebChromiumTest.php
+++ b/tests/e2e/WebChromiumTest.php
@@ -59,6 +59,7 @@ final class WebChromiumTest extends Base
         ...Base::OPTIONAL_PARAM_RESPONSES,
         ...Base::UNION_RESPONSES,
         ...Base::MODEL_DEFAULT_RESPONSES,
+        ...Base::JS_MODEL_TO_STRING_RESPONSES,
         ...Base::EXCEPTION_RESPONSES,
         ...Base::REALTIME_RESPONSES,
         ...Base::QUERY_HELPER_RESPONSES,
diff --git a/tests/e2e/WebNodeTest.php b/tests/e2e/WebNodeTest.php
index aaa4ba98a2..1e5eb87618 100644
--- a/tests/e2e/WebNodeTest.php
+++ b/tests/e2e/WebNodeTest.php
@@ -51,6 +51,7 @@ final class WebNodeTest extends Base
         ...Base::OPTIONAL_PARAM_RESPONSES,
         ...Base::UNION_RESPONSES,
         ...Base::MODEL_DEFAULT_RESPONSES,
+        ...Base::JS_MODEL_TO_STRING_RESPONSES,
         ...Base::EXCEPTION_RESPONSES,
         ...Base::QUERY_HELPER_RESPONSES,
         ...Base::PERMISSION_HELPER_RESPONSES,
diff --git a/tests/e2e/languages/node/test.js b/tests/e2e/languages/node/test.js
index d01e0ecea0..c228753edf 100644
--- a/tests/e2e/languages/node/test.js
+++ b/tests/e2e/languages/node/test.js
@@ -284,6 +284,7 @@ async function start() {
     for (const item of presets.presets) {
         console.log(`preset: name=${item.name}, count=${item.count}, enabled=${item.enabled}`);
     }
+    console.log(`preset toString: ${preset.toString()}`);
 
     try {
         response = await general.error400();
diff --git a/tests/e2e/languages/react-native/browser.js b/tests/e2e/languages/react-native/browser.js
index 19dd4c4461..72a6e5647d 100644
--- a/tests/e2e/languages/react-native/browser.js
+++ b/tests/e2e/languages/react-native/browser.js
@@ -231,6 +231,7 @@ import {
     for (const item of presets.presets) {
         console.log(`preset: name=${item.name}, count=${item.count}, enabled=${item.enabled}`);
     }
+    console.log(`preset toString: ${preset.toString()}`);
 
     // Exception responses
     try {
diff --git a/tests/e2e/languages/web/index.html b/tests/e2e/languages/web/index.html
index 734f322050..05e2f11a22 100644
--- a/tests/e2e/languages/web/index.html
+++ b/tests/e2e/languages/web/index.html
@@ -337,6 +337,7 @@
             for (const item of presets.presets) {
                 console.log(`preset: name=${item.name}, count=${item.count}, enabled=${item.enabled}`);
             }
+            console.log(`preset toString: ${preset.toString()}`);
 
             try {
                 response = await general.error400();
diff --git a/tests/e2e/languages/web/node.js b/tests/e2e/languages/web/node.js
index f5d9adf050..09252ae641 100644
--- a/tests/e2e/languages/web/node.js
+++ b/tests/e2e/languages/web/node.js
@@ -200,6 +200,7 @@ async function start() {
     for (const item of presets.presets) {
         console.log(`preset: name=${item.name}, count=${item.count}, enabled=${item.enabled}`);
     }
+    console.log(`preset toString: ${preset.toString()}`);
 
     try {
         response = await general.error400();