diff --git a/src/shared/components/OAuthModal.js b/src/shared/components/OAuthModal.js
index 751bc065ff2..1f89a0a5ccb 100644
--- a/src/shared/components/OAuthModal.js
+++ b/src/shared/components/OAuthModal.js
@@ -4,6 +4,7 @@ import { useState, useEffect, useRef, useCallback } from "react";
 import PropTypes from "prop-types";
 import { Modal, Button, Input } from "@/shared/components";
 import { useCopyToClipboard } from "@/shared/hooks/useCopyToClipboard";
+import { parseResponseBody, getResponseErrorMessage } from "@/shared/utils/api";
 
 /**
  * OAuth Modal Component
@@ -55,8 +56,8 @@ export default function OAuthModal({ isOpen, provider, providerInfo, onSuccess,
         }),
       });
 
-      const data = await res.json();
-      if (!res.ok) throw new Error(data.error);
+      const data = await parseResponseBody(res);
+      if (!res.ok) throw new Error(getResponseErrorMessage(res, data, "OAuth exchange failed"));
 
       setStep("success");
       onSuccess?.();
@@ -74,8 +75,8 @@ export default function OAuthModal({ isOpen, provider, providerInfo, onSuccess,
         headers: { "Content-Type": "application/json" },
         body: JSON.stringify({ code, state: authData.state }),
       });
-      const data = await res.json();
-      if (!res.ok) throw new Error(data.error);
+      const data = await parseResponseBody(res);
+      if (!res.ok) throw new Error(getResponseErrorMessage(res, data, "xAI manual code exchange failed"));
 
       setStep("success");
       onSuccess?.();
@@ -115,7 +116,8 @@ export default function OAuthModal({ isOpen, provider, providerInfo, onSuccess,
           body: JSON.stringify({ deviceCode, codeVerifier, extraData }),
         });
 
-        const data = await res.json();
+        const data = await parseResponseBody(res);
+        if (!res.ok) throw new Error(getResponseErrorMessage(res, data, "OAuth polling failed"));
 
         if (data.success) {
           pollingAbortRef.current = true; // Stop polling immediately
@@ -166,8 +168,8 @@ export default function OAuthModal({ isOpen, provider, providerInfo, onSuccess,
           deviceCodeUrl.searchParams.set("auth_method", "idc");
         }
         const res = await fetch(deviceCodeUrl.toString());
-        const data = await res.json();
-        if (!res.ok) throw new Error(data.error);
+        const data = await parseResponseBody(res);
+        if (!res.ok) throw new Error(getResponseErrorMessage(res, data, "OAuth device-code request failed"));
 
         setDeviceData(data);
 
@@ -207,8 +209,8 @@ export default function OAuthModal({ isOpen, provider, providerInfo, onSuccess,
         Object.entries(oauthMeta).forEach(([k, v]) => { if (v) authorizeUrl.searchParams.set(k, v); });
       }
       const res = await fetch(authorizeUrl.toString());
-      const data = await res.json();
-      if (!res.ok) throw new Error(data.error);
+      const data = await parseResponseBody(res);
+      if (!res.ok) throw new Error(getResponseErrorMessage(res, data, "OAuth authorization failed"));
 
       // Codex: start proxy with server-side session (auto-exchange) + fallback to channels
       let codexProxyActive = false;
@@ -221,7 +223,8 @@ export default function OAuthModal({ isOpen, provider, providerInfo, onSuccess,
           proxyUrl.searchParams.set("code_verifier", data.codeVerifier);
           proxyUrl.searchParams.set("redirect_uri", redirectUri);
           const proxyRes = await fetch(proxyUrl.toString());
-          const proxyData = await proxyRes.json();
+          const proxyData = await parseResponseBody(proxyRes);
+          if (!proxyRes.ok) throw new Error(getResponseErrorMessage(proxyRes, proxyData, "Codex OAuth proxy failed"));
           codexProxyActive = proxyData.success;
           codexServerSide = !!proxyData.serverSide;
         } catch {
@@ -240,7 +243,8 @@ export default function OAuthModal({ isOpen, provider, providerInfo, onSuccess,
           proxyUrl.searchParams.set("code_verifier", data.codeVerifier);
           proxyUrl.searchParams.set("redirect_uri", redirectUri);
           const proxyRes = await fetch(proxyUrl.toString());
-          const proxyData = await proxyRes.json();
+          const proxyData = await parseResponseBody(proxyRes);
+          if (!proxyRes.ok) throw new Error(getResponseErrorMessage(proxyRes, proxyData, "Grok Build OAuth proxy failed"));
           xaiProxyActive = proxyData.success;
           xaiServerSide = !!proxyData.serverSide;
           if (!xaiProxyActive && proxyData.reason === "port_busy") {
@@ -321,8 +325,9 @@ export default function OAuthModal({ isOpen, provider, providerInfo, onSuccess,
       if (cancelled || callbackProcessedRef.current) return;
       attempts += 1;
       try {
-          const res = await fetch(`/api/oauth/${pollProvider}/poll-status?state=${encodeURIComponent(authData.state)}`);
-        const data = await res.json();
+        const res = await fetch(`/api/oauth/${pollProvider}/poll-status?state=${encodeURIComponent(authData.state)}`);
+        const data = await parseResponseBody(res);
+        if (!res.ok) throw new Error(getResponseErrorMessage(res, data, "OAuth status polling failed"));
         if (cancelled || callbackProcessedRef.current) return;
         if (data.status === "done") {
           callbackProcessedRef.current = true;
diff --git a/src/shared/utils/api.js b/src/shared/utils/api.js
index 5712ef9eeb8..aff24fdd125 100644
--- a/src/shared/utils/api.js
+++ b/src/shared/utils/api.js
@@ -75,11 +75,36 @@ export async function del(url, options = {}) {
  * @param {Response} response - Fetch response
  * @returns {Promise<object>}
  */
-async function handleResponse(response) {
-  const data = await response.json();
+export async function parseResponseBody(response) {
+  const text = await response.text();
+  if (!text) return {};
+
+  try {
+    return JSON.parse(text);
+  } catch {
+    return { error: text.trim() || "Invalid non-JSON response", rawText: text };
+  }
+}
+
+export function getResponseErrorMessage(response, data = {}, fallback = "Request failed") {
+  const rawError = data.error || data.errorDescription || data.message;
+  const message = typeof rawError === "object"
+    ? rawError.message || JSON.stringify(rawError)
+    : rawError;
+  const cleanMessage = String(message || fallback).trim();
+  if (!response) return cleanMessage;
+
+  const statusLabel = response.status
+    ? `${response.status}${response.statusText ? ` ${response.statusText}` : ""}`
+    : "";
+  return statusLabel ? `${fallback} (${statusLabel}): ${cleanMessage}` : cleanMessage;
+}
+
+export async function handleResponse(response) {
+  const data = await parseResponseBody(response);
 
   if (!response.ok) {
-    const error = new Error(data.error || "An error occurred");
+    const error = new Error(getResponseErrorMessage(response, data, "An error occurred"));
     error.status = response.status;
     error.data = data;
     throw error;
diff --git a/tests/unit/api-response.test.js b/tests/unit/api-response.test.js
new file mode 100644
index 00000000000..1f2cf619ff2
--- /dev/null
+++ b/tests/unit/api-response.test.js
@@ -0,0 +1,47 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  getResponseErrorMessage,
+  handleResponse,
+  parseResponseBody,
+} from "../../src/shared/utils/api.js";
+
+describe("shared API response helpers", () => {
+  it("parses JSON responses", async () => {
+    const response = new Response(JSON.stringify({ ok: true }), {
+      status: 200,
+      headers: { "Content-Type": "application/json" },
+    });
+
+    await expect(parseResponseBody(response)).resolves.toEqual({ ok: true });
+  });
+
+  it("turns non-JSON error responses into usable error data", async () => {
+    const response = new Response("Internal Server Error", {
+      status: 500,
+      statusText: "Internal Server Error",
+      headers: { "Content-Type": "text/plain" },
+    });
+
+    const data = await parseResponseBody(response);
+
+    expect(data.error).toBe("Internal Server Error");
+    expect(getResponseErrorMessage(response, data, "OAuth authorization failed")).toBe(
+      "OAuth authorization failed (500 Internal Server Error): Internal Server Error"
+    );
+  });
+
+  it("throws structured errors for JSON API failures", async () => {
+    const response = new Response(JSON.stringify({ error: "Nope" }), {
+      status: 400,
+      statusText: "Bad Request",
+      headers: { "Content-Type": "application/json" },
+    });
+
+    await expect(handleResponse(response)).rejects.toMatchObject({
+      message: "An error occurred (400 Bad Request): Nope",
+      status: 400,
+      data: { error: "Nope" },
+    });
+  });
+});