diff --git a/full-sync.js b/full-sync.js
index 8ba1c7353..930f191a0 100644
--- a/full-sync.js
+++ b/full-sync.js
@@ -1,16 +1,32 @@
 const appFn = require('./')
 const { FULL_SYNC_NOP } = require('./lib/env')
 const { createProbot } = require('probot')
+const pino = require('pino')
 
 async function performFullSync (appFn, nop) {
-  const probot = createProbot()
+  const logLevel = process.env.LOG_LEVEL || 'info'
+  const logger = pino({
+    level: logLevel,
+    transport: {
+      target: 'pino-pretty',
+      options: {
+        colorize: true,
+        ignore: 'pid,hostname',
+        messageFormat: '{msg}',
+        customColors: 'info:blue,warn:yellow,error:red',
+        levelFirst: true
+      }
+    }
+  })
+
+  const probot = createProbot({ overrides: { log: logger } })
   probot.log.info(`Starting full sync with NOP=${nop}`)
 
   try {
     const app = appFn(probot, {})
     const settings = await app.syncInstallation(nop)
 
-    if (settings.errors && settings.errors.length > 0) {
+    if (settings && settings.errors && settings.errors.length > 0) {
       probot.log.error('Errors occurred during full sync.')
       process.exit(1)
     }
@@ -22,7 +38,13 @@ async function performFullSync (appFn, nop) {
   }
 }
 
-performFullSync(appFn, FULL_SYNC_NOP).catch((error) => {
-  console.error('Fatal error during full sync:', error)
-  process.exit(1)
-})
+// Only run if executed directly (not when imported for testing)
+if (require.main === module) {
+  performFullSync(appFn, FULL_SYNC_NOP).catch((error) => {
+    console.error('Fatal error during full sync:', error)
+    process.exit(1)
+  })
+}
+
+// Export for testing
+module.exports = { performFullSync }
diff --git a/package-lock.json b/package-lock.json
index cdb557108..19d3a6dd1 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -18,6 +18,8 @@
         "minimatch": "^10.2.1",
         "node-cron": "^4.2.1",
         "octokit": "^5.0.2",
+        "pino": "^10.3.1",
+        "pino-pretty": "^13.1.3",
         "probot": "^14.2.4",
         "proxy-from-env": "^2.1.0",
         "undici": "^7.7.0"
diff --git a/package.json b/package.json
index 302f9f205..705a909b3 100644
--- a/package.json
+++ b/package.json
@@ -34,6 +34,8 @@
     "minimatch": "^10.2.1",
     "node-cron": "^4.2.1",
     "octokit": "^5.0.2",
+    "pino": "^10.3.1",
+    "pino-pretty": "^13.1.3",
     "probot": "^14.2.4",
     "proxy-from-env": "^2.1.0",
     "undici": "^7.7.0"
diff --git a/test/unit/full-sync.test.js b/test/unit/full-sync.test.js
new file mode 100644
index 000000000..584c07df4
--- /dev/null
+++ b/test/unit/full-sync.test.js
@@ -0,0 +1,41 @@
+const { performFullSync } = require('../../full-sync')
+
+jest.mock('probot', () => ({
+  createProbot: jest.fn()
+}))
+jest.mock('pino', () => jest.fn(() => ({ info: jest.fn() })))
+
+describe('full-sync.js', () => {
+  let mockApp
+
+  beforeEach(() => {
+    jest.clearAllMocks()
+    require('probot').createProbot.mockImplementation(({ overrides }) => ({
+      log: overrides.log
+    }))
+    mockApp = { syncInstallation: jest.fn() }
+  })
+
+  it('should pass logger to createProbot via overrides (v14 fix)', async () => {
+    mockApp.syncInstallation.mockResolvedValue({ errors: [] })
+    await performFullSync(jest.fn().mockReturnValue(mockApp), true)
+
+    expect(require('probot').createProbot).toHaveBeenCalledWith(
+      expect.objectContaining({
+        overrides: expect.objectContaining({ log: expect.any(Object) })
+      })
+    )
+  })
+
+  it('should handle null settings without crashing (null safety)', async () => {
+    mockApp.syncInstallation.mockResolvedValue(null)
+    const mockLogger = { info: jest.fn(), error: jest.fn() }
+    require('pino').mockReturnValueOnce(mockLogger)
+    require('probot').createProbot.mockImplementationOnce(({ overrides }) => ({
+      log: overrides.log
+    }))
+    await performFullSync(jest.fn().mockReturnValue(mockApp), true)
+
+    expect(mockLogger.info).toHaveBeenCalledWith('Full sync completed successfully.')
+  })
+})