Tension Ninja

Measure String Bed Tension Using Only Your Microphone

How much tension does your string bed really have left? Tension Ninja tells you in seconds—using nothing but your smartphone's microphone. No expensive measuring device. No cables.

How it works

Simply hold your racket flat, tap the strings, and let the app record the sound. It analyzes the vibration frequency and calculates your current string tension in kilograms—accurately and in real time.

FOR ANY RACKET AND ANY STRING

Manage as many rackets and string types as you like. The app takes racket head size and string pattern into account for highly accurate results. Hybrid string setups with different main and cross strings are fully supported.

TRACK TENSION LOSS

Strings gradually lose tension over time. Tension Ninja stores every measurement and displays the history in an easy-to-read chart, so you'll always know when it's time to restring.

NFC TAG SUPPORT FOR STRINGERS AND PRO SHOPS

Assign an NFC tag to each racket and link it to a customer, racket, and stringing setup. Simply tap the tag with your phone, and the app instantly loads the correct configuration. Perfect for clubs, professional stringers, and tennis shops managing multiple rackets.

CUSTOMER & STRINGING JOB MANAGEMENT

Create customer profiles, document their rackets and stringing jobs, and keep track of every recorded tension measurement for each job—all in one place.

COMPLETELY OFFLINE & PRIVATE

Your data stays on your device. No registration. No cloud account. No data collection. The app works entirely offline.

AVAILABLE IN 8 LANGUAGES

English, German, Spanish, French, Italian, Portuguese, Russian, and Chinese.

Whether you're a dedicated recreational player who wants to keep track of your string tension or a professional stringer managing dozens of customer rackets, Tension Ninja makes string tension visible.

Download now and discover the true tension of your strings.