diff --git a/src/lib/node-oauth-client-provider.ts b/src/lib/node-oauth-client-provider.ts
index 806f3af..0826844 100644
--- a/src/lib/node-oauth-client-provider.ts
+++ b/src/lib/node-oauth-client-provider.ts
@@ -1,9 +1,8 @@
 import open from 'open'
 import { OAuthClientProvider } from '@modelcontextprotocol/sdk/client/auth.js'
 import {
-  OAuthClientInformation,
   OAuthClientInformationFull,
-  OAuthClientInformationSchema,
+  OAuthClientInformationFullSchema,
   OAuthTokens,
   OAuthTokensSchema,
 } from '@modelcontextprotocol/sdk/shared/auth.js'
@@ -57,9 +56,9 @@ export class NodeOAuthClientProvider implements OAuthClientProvider {
    * Gets the client information if it exists
    * @returns The client information or undefined
    */
-  async clientInformation(): Promise<OAuthClientInformation | undefined> {
+  async clientInformation(): Promise<OAuthClientInformationFull | undefined> {
     // log('Reading client info')
-    return readJsonFile<OAuthClientInformation>(this.serverUrlHash, 'client_info.json', OAuthClientInformationSchema)
+    return readJsonFile<OAuthClientInformationFull>(this.serverUrlHash, 'client_info.json', OAuthClientInformationFullSchema)
   }
 
   /**
diff --git a/src/lib/utils.ts b/src/lib/utils.ts
index b11c9b3..7727f68 100644
--- a/src/lib/utils.ts
+++ b/src/lib/utils.ts
@@ -6,6 +6,8 @@ import { Transport } from '@modelcontextprotocol/sdk/shared/transport.js'
 import fs from 'fs'
 import path from 'path'
 import os from 'os'
+import { OAuthClientInformationFull, OAuthClientInformationFullSchema } from '@modelcontextprotocol/sdk/shared/auth.js'
+
 
 // Connection constants
 export const REASON_AUTH_NEEDED = 'authentication-needed'
@@ -15,6 +17,7 @@ export const SHORT_TIMEOUT_DURATION = 50000
 // Transport strategy types
 export type TransportStrategy = 'sse-only' | 'http-only' | 'sse-first' | 'http-first'
 import { OAuthCallbackServerOptions } from './types'
+import { readJsonFile } from './mcp-auth-config'
 import express from 'express'
 import net from 'net'
 import crypto from 'crypto'
@@ -399,6 +402,21 @@ export function setupOAuthCallbackServer(options: OAuthCallbackServerOptions) {
   return { server, authCode, waitForAuthCode }
 }
 
+async function findExistingClientPort(serverUrl: string): Promise<number | undefined> {
+  const serverUrlHash = getServerUrlHash(serverUrl)
+  const clientInfo = await readJsonFile<OAuthClientInformationFull>(serverUrlHash, 'client_info.json', OAuthClientInformationFullSchema)
+  if (!clientInfo) {
+    return undefined
+  }
+
+  const localhostRedirectUri = clientInfo.redirect_uris.map((uri) => new URL(uri)).find(({ hostname }) => hostname === 'localhost')
+  if (!localhostRedirectUri) {
+    throw new Error('Cannot find localhost callback URI from existing client information')
+  }
+
+  return parseInt(localhostRedirectUri.port)
+}
+
 /**
  * Finds an available port on the local machine
  * @param preferredPort Optional preferred port to try first
@@ -488,11 +506,14 @@ export async function parseCommandLineArgs(args: string[], defaultPort: number,
     process.exit(1)
   }
 
-  // Use the specified port, or find an available one
-  const callbackPort = specifiedPort || (await findAvailablePort(defaultPort))
+  // Use the specified port, or the existing client port or fallback to find an available one
+  const [existingClientPort, availablePort] = await Promise.all([findExistingClientPort(serverUrl), findAvailablePort(defaultPort)])
+  const callbackPort = specifiedPort || existingClientPort || availablePort
 
   if (specifiedPort) {
     log(`Using specified callback port: ${callbackPort}`)
+  } else if (existingClientPort) {
+    log(`Using existing client port: ${existingClientPort}`)
   } else {
     log(`Using automatically selected callback port: ${callbackPort}`)
   }