diff --git a/src/api/routes/mcp.js b/src/api/routes/mcp.js
index 30064e6..6500b26 100644
--- a/src/api/routes/mcp.js
+++ b/src/api/routes/mcp.js
@@ -20,6 +20,56 @@ function getBaseUrl(req) {
     return `${proto}://${host}`;
 }
 
+/**
+ * Checks if a candidate redirect_uri matches any registered redirect URI.
+ * Per RFC 8252 Section 7.3 (OAuth 2.0 for Native Apps):
+ * "The authorization server MUST allow any port for loopback IP redirect URIs."
+ * @param {string} candidateUri
+ * @param {Array<string>|string} registeredUris
+ * @returns {boolean}
+ */
+function isRedirectUriAllowed(candidateUri, registeredUris) {
+    if (!candidateUri || !registeredUris) return false;
+    const uriList = Array.isArray(registeredUris) ? registeredUris : [registeredUris];
+    if (uriList.includes(candidateUri)) return true;
+
+    try {
+        const candidate = new URL(candidateUri);
+        const isCandidateLoopback = candidate.hostname === '127.0.0.1' || candidate.hostname === 'localhost';
+
+        for (const reg of uriList) {
+            try {
+                const registered = new URL(reg);
+                const normCandidatePath = candidate.pathname.replace(/\/$/, '');
+                const normRegisteredPath = registered.pathname.replace(/\/$/, '');
+
+                if (
+                    candidate.origin === registered.origin &&
+                    normCandidatePath === normRegisteredPath
+                ) {
+                    return true;
+                }
+
+                const isRegisteredLoopback = registered.hostname === '127.0.0.1' || registered.hostname === 'localhost';
+                if (
+                    isCandidateLoopback &&
+                    isRegisteredLoopback &&
+                    candidate.protocol === registered.protocol &&
+                    normCandidatePath === normRegisteredPath
+                ) {
+                    return true;
+                }
+            } catch {
+                // Ignore malformed registered URI
+            }
+        }
+    } catch {
+        return false;
+    }
+
+    return false;
+}
+
 const tokenVerifier = {
     verifyAccessToken: async (token) => {
         let decoded;
@@ -325,7 +375,7 @@ export function register(app, _basePath = '') {
             registeredUris = [client.redirectUris];
         }
 
-        if (!redirect_uri || !registeredUris.includes(redirect_uri)) {
+        if (!redirect_uri || !isRedirectUriAllowed(redirect_uri, registeredUris)) {
             return res.status(400).send('Invalid or unregistered redirect_uri');
         }
 
@@ -543,7 +593,7 @@ export function register(app, _basePath = '') {
                     });
                 }
 
-                if (authCode.redirectUri !== redirect_uri) {
+                if (!isRedirectUriAllowed(redirect_uri, [authCode.redirectUri])) {
                     return res.status(400).json({
                         error: 'invalid_grant',
                         error_description: 'Redirect URI does not match authorization code',