diff --git a/clients/web/src/App.tsx b/clients/web/src/App.tsx
index 044e2e961..2903d606f 100644
--- a/clients/web/src/App.tsx
+++ b/clients/web/src/App.tsx
@@ -32,6 +32,10 @@ import { MessageLogState } from "@inspector/core/mcp/state/messageLogState.js";
 import { FetchRequestLogState } from "@inspector/core/mcp/state/fetchRequestLogState.js";
 import { StderrLogState } from "@inspector/core/mcp/state/stderrLogState.js";
 import type { RedirectUrlProvider } from "@inspector/core/auth/index.js";
+import {
+  parseOAuthCallbackParams,
+  generateOAuthErrorDescription,
+} from "@inspector/core/auth/index.js";
 import { useInspectorClient } from "@inspector/core/react/useInspectorClient.js";
 import { useServers } from "@inspector/core/react/useServers.js";
 import { useSettingsDraft } from "@inspector/core/react/useSettingsDraft.js";
@@ -59,13 +63,18 @@ import type { OAuthDetails } from "./components/groups/ConnectionInfoContent/Con
 import { ServerRemoveConfirmModal } from "./components/groups/ServerRemoveConfirmModal/ServerRemoveConfirmModal";
 import { buildExportFilename, downloadJsonFile } from "./lib/downloadFile";
 import { createWebEnvironment } from "./lib/environmentFactory";
+import {
+  OAUTH_CALLBACK_PATH,
+  OAUTH_PENDING_SERVER_KEY,
+  isUnauthorizedError,
+} from "./utils/oauthFlow";
 
 // OAuth redirect URL provider — points at the dev backend's `/oauth/callback`
 // handler. The InspectorClient only consults this when the active server
 // requires OAuth; for stdio MCP servers it's never used. Created once and
 // reused so `BrowserOAuthClientProvider` doesn't re-instantiate per render.
 const redirectUrlProvider: RedirectUrlProvider = {
-  getRedirectUrl: () => `${window.location.origin}/oauth/callback`,
+  getRedirectUrl: () => `${window.location.origin}${OAUTH_CALLBACK_PATH}`,
 };
 
 // Recover the backend's auth token. Every browser request to /api/* needs it
@@ -259,6 +268,11 @@ function App() {
   const connectStartRef = useRef<number | undefined>(undefined);
   const [latencyMs, setLatencyMs] = useState<number | undefined>(undefined);
 
+  // One-shot guard for the `/oauth/callback` handler below. The effect waits
+  // for the async `servers` list to hydrate, so it can run on more than one
+  // render; this ref ensures the token exchange fires exactly once per load.
+  const oauthCallbackHandledRef = useRef(false);
+
   // Hook layer. Each hook subscribes to its respective event source and
   // re-renders the App on change. When `inspectorClient` / state managers
   // are null, the hooks degrade to empty results.
@@ -542,6 +556,95 @@ function App() {
     ],
   );
 
+  // Finish the OAuth authorization-code flow when the auth server redirects
+  // back to `/oauth/callback`. This runs on a fresh page load (the redirect in
+  // `onToggleConnection` unloaded the previous one), so all React state is
+  // reset and we recover the initiating server from sessionStorage. We wait for
+  // `servers` to hydrate before acting; the ref guard keeps the exchange to a
+  // single run. The persisted PKCE verifier + DCR client info live in
+  // `BrowserOAuthStorage` and survive the redirect, so `completeOAuthFlow`
+  // exchanges the code without needing the original in-memory state machine.
+  useEffect(() => {
+    if (typeof window === "undefined") return;
+    if (window.location.pathname !== OAUTH_CALLBACK_PATH) return;
+    if (oauthCallbackHandledRef.current) return;
+    // `useServers` returns [] until the first fetch resolves; defer until the
+    // list is populated so `find` can resolve the pending server.
+    if (servers.length === 0) return;
+    oauthCallbackHandledRef.current = true;
+
+    const params = parseOAuthCallbackParams(window.location.search);
+    const pendingId =
+      window.sessionStorage.getItem(OAUTH_PENDING_SERVER_KEY) ?? undefined;
+    window.sessionStorage.removeItem(OAUTH_PENDING_SERVER_KEY);
+
+    // Strip the code/state off the URL immediately so a reload can't replay
+    // the (now single-use) authorization code through the exchange again.
+    window.history.replaceState({}, "", "/");
+
+    if (!params.successful) {
+      notifications.show({
+        title: "OAuth authorization failed",
+        message: generateOAuthErrorDescription(params),
+        color: "red",
+      });
+      return;
+    }
+
+    // By design, the pending id and URL are cleared above before this lookup:
+    // if the server was deleted/renamed (e.g. in another tab) mid-flow, there's
+    // nothing to resume against, so we surface the error and require a fresh
+    // Connect rather than leaving stale callback state lying around.
+    const server = pendingId
+      ? servers.find((s) => s.id === pendingId)
+      : undefined;
+    if (!server) {
+      notifications.show({
+        title: "OAuth callback could not be matched",
+        message:
+          "Could not determine which server started the OAuth flow. Please try connecting again.",
+        color: "red",
+      });
+      return;
+    }
+
+    void (async () => {
+      const client = setupClientForServer(server);
+      setActiveServerId(server.id);
+      // Two distinct failure modes get distinct toasts. A token-exchange
+      // failure means OAuth did NOT complete — and since the single-use code
+      // is spent and the URL was already cleared, a reload can't retry, so we
+      // tell the user to start over. A failure in the subsequent connect()
+      // means OAuth DID complete (tokens are persisted): it's a transport
+      // problem, and re-clicking Connect reuses the saved tokens (no second
+      // authorization). Conflating them would mislead the user into
+      // re-authorizing when they don't need to.
+      try {
+        await client.completeOAuthFlow(params.code);
+      } catch (err) {
+        const message = err instanceof Error ? err.message : String(err);
+        notifications.show({
+          title: `OAuth token exchange failed for "${server.name}"`,
+          message: `${message}\n\nPlease try connecting again.`,
+          color: "red",
+        });
+        return;
+      }
+      try {
+        connectStartRef.current = Date.now();
+        await client.connect();
+      } catch (err) {
+        connectStartRef.current = undefined;
+        const message = err instanceof Error ? err.message : String(err);
+        notifications.show({
+          title: `Failed to connect to "${server.name}"`,
+          message,
+          color: "red",
+        });
+      }
+    })();
+  }, [servers, setupClientForServer]);
+
   const onToggleConnection = useCallback(
     async (id: string) => {
       // Same server, already connected → disconnect.
@@ -577,11 +680,37 @@ function App() {
       } catch (err) {
         // Handshake-only. A mid-session transport failure does not throw,
         // so a future error event from InspectorClient is the right hook
-        // for surfacing those (TODO(#1323)). For now: toast on the
-        // handshake error so the user actually sees what went wrong
+        // for surfacing those (TODO(#1323)).
+        connectStartRef.current = undefined;
+
+        // A 401 from an OAuth-protected server means we have no (valid) token
+        // yet. Kick off the authorization-code flow: `authenticate()` runs
+        // discovery + DCR (proxied through the backend), then redirects the
+        // whole page to the auth server via `BrowserNavigation`. Persist the
+        // initiating server id first so the `/oauth/callback` load can resume
+        // against the right client. The redirect unloads this page, so there's
+        // nothing to do after the await on the success path.
+        if (isUnauthorizedError(err)) {
+          try {
+            window.sessionStorage.setItem(OAUTH_PENDING_SERVER_KEY, id);
+            await client.authenticate();
+            return;
+          } catch (authErr) {
+            window.sessionStorage.removeItem(OAUTH_PENDING_SERVER_KEY);
+            const message =
+              authErr instanceof Error ? authErr.message : String(authErr);
+            notifications.show({
+              title: `OAuth authorization failed for "${target.name}"`,
+              message,
+              color: "red",
+            });
+            return;
+          }
+        }
+
+        // Non-auth handshake error: toast so the user sees what went wrong
         // instead of the ConnectionToggle silently reverting to
         // "disconnected".
-        connectStartRef.current = undefined;
         const message = err instanceof Error ? err.message : String(err);
         notifications.show({
           title: `Failed to connect to "${target.name}"`,
diff --git a/clients/web/src/utils/oauthFlow.test.ts b/clients/web/src/utils/oauthFlow.test.ts
new file mode 100644
index 000000000..9896edd7b
--- /dev/null
+++ b/clients/web/src/utils/oauthFlow.test.ts
@@ -0,0 +1,68 @@
+import { describe, it, expect } from "vitest";
+import {
+  OAUTH_CALLBACK_PATH,
+  OAUTH_PENDING_SERVER_KEY,
+  isUnauthorizedError,
+} from "./oauthFlow";
+
+describe("oauthFlow constants", () => {
+  it("uses the redirect path the providers expect", () => {
+    expect(OAUTH_CALLBACK_PATH).toBe("/oauth/callback");
+  });
+
+  it("namespaces the pending-server key", () => {
+    expect(OAUTH_PENDING_SERVER_KEY).toBe(
+      "mcp-inspector:oauth-pending-server-id",
+    );
+  });
+});
+
+describe("isUnauthorizedError", () => {
+  it("detects a 401 carried on error.status", () => {
+    const err = Object.assign(new Error("Remote send failed"), { status: 401 });
+    expect(isUnauthorizedError(err)).toBe(true);
+  });
+
+  it("detects a 401 carried on error.code", () => {
+    const err = Object.assign(new Error("boom"), { code: 401 });
+    expect(isUnauthorizedError(err)).toBe(true);
+  });
+
+  it("detects a 401 formatted into the message when status is lost", () => {
+    const err = new Error(
+      'Remote send failed (401): {"error":"invalid_token","error_description":"Missing Authorization header"}',
+    );
+    expect(isUnauthorizedError(err)).toBe(true);
+  });
+
+  it("matches a 401 in a plain (non-Error) thrown value", () => {
+    expect(isUnauthorizedError("Remote connect failed (401): nope")).toBe(true);
+  });
+
+  it("does not treat other status codes as unauthorized", () => {
+    const err = Object.assign(new Error("Remote send failed (500): boom"), {
+      status: 500,
+    });
+    expect(isUnauthorizedError(err)).toBe(false);
+  });
+
+  it("does not match a bare 401 substring that isn't the formatted status", () => {
+    // The transport formats the status as "(401)"; a 401 appearing elsewhere
+    // (e.g. inside an id or token) must not be mistaken for an auth failure.
+    const err = new Error("tool returned value 40123 for request");
+    expect(isUnauthorizedError(err)).toBe(false);
+  });
+
+  it("does not match a stray '(401)' that isn't the transport's 'failed' wording", () => {
+    // A tool result or unrelated message embedding `(401)` without the
+    // transport's `failed …(401)` shape must not trip the OAuth flow.
+    const err = new Error("tool output: response code (401) seen upstream");
+    expect(isUnauthorizedError(err)).toBe(false);
+  });
+
+  it("returns false for null / undefined / non-401 primitives", () => {
+    expect(isUnauthorizedError(null)).toBe(false);
+    expect(isUnauthorizedError(undefined)).toBe(false);
+    expect(isUnauthorizedError(42)).toBe(false);
+  });
+});
diff --git a/clients/web/src/utils/oauthFlow.ts b/clients/web/src/utils/oauthFlow.ts
new file mode 100644
index 000000000..928ccd250
--- /dev/null
+++ b/clients/web/src/utils/oauthFlow.ts
@@ -0,0 +1,44 @@
+/**
+ * Shared constants and predicates for the browser-side OAuth authorization-code
+ * flow wired into `App.tsx`. Extracted here so the pure logic is unit-testable
+ * independently of the React component that orchestrates it.
+ */
+
+/**
+ * The pathname the auth server redirects back to after the user authorizes.
+ * `App.tsx`'s `redirectUrlProvider` points OAuth flows at
+ * `${origin}${OAUTH_CALLBACK_PATH}`; the mount effect detects this pathname and
+ * finishes the token exchange.
+ */
+export const OAUTH_CALLBACK_PATH = "/oauth/callback";
+
+/**
+ * sessionStorage key holding the id of the server whose OAuth flow is in
+ * flight. The OAuth `state` parameter only carries `{mode}:{authId}`, not which
+ * configured server initiated the flow, and the full-page redirect to the auth
+ * server wipes all in-memory React state. The id is stashed here right before
+ * redirecting so the post-callback page load can rebuild the right
+ * `InspectorClient` and resume the connection.
+ */
+export const OAUTH_PENDING_SERVER_KEY = "mcp-inspector:oauth-pending-server-id";
+
+/**
+ * True when a thrown connect error represents an upstream 401. The remote
+ * transport preserves the status on the error object
+ * (`remoteClientTransport` sets `error.status`); this structured check is the
+ * primary path. As a fallback for cases where the status is lost crossing an
+ * SDK boundary, we match the transport's own formatted wording —
+ * `"Remote (connect|send|events stream) failed (401): …"` — anchored on
+ * `failed …(401)` rather than a bare `(401)`, so an unrelated `(401)` spliced
+ * into an error message (e.g. from a tool result) can't trip the OAuth flow.
+ * A 401 on connect to an HTTP/SSE server is the signal to start OAuth.
+ */
+export function isUnauthorizedError(err: unknown): boolean {
+  if (typeof err === "object" && err !== null) {
+    const status = (err as { status?: number; code?: number }).status;
+    const code = (err as { code?: number }).code;
+    if (status === 401 || code === 401) return true;
+  }
+  const message = err instanceof Error ? err.message : String(err);
+  return /\bfailed\b[^\n]*\(401\)/i.test(message);
+}