CDL One Stop — Support

Real help from the people who built the app. Tell us what you need and we'll get you back on the road to your CDL.

Get in touch

Questions, feedback, or trouble with the app? Email our team directly and we'll personally help you sort it out.

We typically reply within 1–2 business days.

Email Support

harmonyStack@gmail.com

Frequently asked

Answers to common questions

Which license and tests does the app cover?

CDL One Stop covers the CDL knowledge exam for all 50 states + DC, across Class A, B, and C — Core Knowledge, Endorsements, Combination, and the Pre-Trip Inspection — across 13 study areas.

How does the readiness score work?

Your readiness percentage blends your accuracy with how much of each question bank you've actually seen. Reaching 100% means you've consistently passed practice across every area.

Is my progress saved?

Yes. Your streaks, levels, key dates, and missed questions are kept on your device so you can pick up where you left off.

How do I set my test date?

On the Study tab, tap "Set up your key dates" to add your exam date and study toward a countdown.

I think an answer is wrong, or I hit a bug.

Please email us at harmonyStack@gmail.com with the question text and a screenshot — we review every report.

Is the app available on the App Store?

Yes — CDL One Stop is live on the App Store, now covering all 50 states + DC across Class A, B, and C.

CDL One Stop is live on the App Store — all 50 states + DC, Class A, B & C.

Still need help?

We're a small team and we read every message. Reach out any time and a real person will get back to you.

Email harmonyStack@gmail.com

Your privacy

We respect your privacy. CDL One Stop does not sell your personal information. Your study progress — streaks, levels, key dates, and missed questions — is kept on your device.

If you email us for support, we only use your message to help you and reply. For any privacy questions, email us at harmonyStack@gmail.com.

The full details — what stays on your device, what an optional account stores, and how to have anything deleted — are in our Privacy Policy. The rules for using the app are in our Terms of Service.