Tap your strings. Get an instant tension reading from just your iPhone. Know exactly when to restring — and at what tension — so every match starts with strings that actually perform.
iPhone · iOS 17+ · Android coming soon — get notified →
Multi-stage measurement analysis
Signal and quality checks evaluate each measurement before a result is saved
No accessory required
Just your iPhone and your racquet. Nothing to buy, clip on, or charge.
On-device by default
Stringbed audio is analyzed on your iPhone and your records stay local unless you turn on iCloud sync.
Free to measure
Core tension readings are free, forever. No paywall for the fundamentals.
Your iPhone is already a
string tension meter
Multi-stage measurement analysis
Multiple signal and quality checks evaluate each measurement before a result is saved, helping reject weak taps and improve measurement consistency. Acoustic measurement built for consistent tracking.
Real-time Quality Coach
The app gives real-time feedback when the room is too noisy, a tap is too soft, or capture conditions reduce measurement quality. Candidate taps that fail quality checks are rejected before a result is saved.
From string taps to a trackable estimate
Hold your racquet near your iPhone, tap the strings, and let acoustic analysis do the rest.
Tap Your Strings
Hold your racquet near the iPhone mic and tap the string bed 3–10 times. The Quality Coach guides you in real time.
Instant Analysis
Advanced acoustic analysis captures the response and combines its signal with racquet and string inputs to produce a modeled current-tension estimate. All processing happens instantly on your iPhone.
Track & Optimize
See your modeled tension estimate with capture-quality feedback. Track decay over time. Get AI-powered restring recommendations.
Tension changes
everything about your game
String tension isn't just a number your stringer sets and you forget. It directly controls how your racquet performs on every single shot.
Power
Lower tension means more power. Strings act like a trampoline — a 4 lb drop can add measurable speed to your serve and groundstrokes.
Spin
Lower tension allows more string movement, which means more spin potential. The sweet spot depends on your string type and swing speed.
Control
Higher tension gives you a smaller sweet spot but more precision. Competitive players often trade power for placement at critical moments.
Comfort
Too-high tension sends more shock to your arm. Finding the right tension protects against tennis elbow, wrist fatigue, and shoulder strain.
You're guessing.
Every single time.
Polyester strings begin losing tension immediately, with much of their time-based settling happening early. Ball impacts add further change, so the stringbed you play after several sessions is not the one that left the machine. String Tension AI helps you follow that trend — so you can recognize when the response leaves your preferred range.
You've tried. We know.
"I just squeeze the strings"
The squeeze test can't detect a 4 lb difference — but your game can. Human fingers aren't tension meters. You need actual numbers, not a vague feeling.
"I restring every X weeks"
Calendar-based restringing ignores how you play, where you play, and what your strings actually need. One size doesn't fit all — and you're either wasting money or playing with dead strings.
"I bought a tension meter"
Electronic tension meters cost $200+. They give you one reading at a time with no tracking, no history, no decay prediction, and no recommendations. Your iPhone can do better.
Your iPhone already has everything it needs. Stop compromising — start measuring what's really happening to your strings.
Your strings lose tension
more than you think
After every measurement, String Tension AI shows how your strings are changing — tension loss percentage, decay rate, capture-quality feedback, and when you may want to restring.
Illustrative signal and model quality indicator, not percentage accuracy versus a stringing machine.
Knows when and at
what tension to restring
The Tension Advisor analyzes your playing history, court surface, weather, arm health, and priorities to suggest the ideal tension for your next restring — with transparent reasoning.
Way more than
a tension meter
Measurement is just the beginning. String Tension AI is a complete string management platform.
📈 Know When Your Strings Die
See exactly how fast your strings are losing tension and when they'll drop below your comfort zone. The app tracks every string job and tells you the optimal day to restring — before your game suffers.
💰 Stop Overspending on Strings
Track what you spend on strings and restringing per year. See breakdowns by string type and stringer. Find out if you're restringing too early, too late, or wasting money on the wrong setup.
🏆 See What the Pros Use
Browse 69 sourced ATP, WTA, and legend string setups plus 29 pro racquet setups. Search by player, country, or brand, and check the last-verified date before you copy anyone.
⚔️ Find Your Perfect String
Compare any two strings side by side — tension retention, performance, cost per day, and annual savings. See which string actually holds up better for your playing style.
🔥 Stay Consistent, Get Rewarded
Log sessions, build streaks, and hit weekly goals. Celebrate milestone unlocks and share milestone cards for free. PRO adds the full gallery of 38 milestones, rank-up celebrations, and approaching-milestone nudges.
☁️ Share With Your Stringer
Save the people who string your racquets and attach one to every job. Share a reading as text or as one of eight visual cards. PDF reports, CSV export, and iCloud sync across devices come with PRO.
🍎 Bring In Your Apple Health Workouts
Already logging tennis in Apple Health? Import those workouts as playing sessions through a review inbox where you keep or remove each one. Health-sourced sessions stay on your device and are never pushed to iCloud.
💬 Ask the String AI Coach
Chat with Apple's on-device model about your own racquets and strings. Every figure it shows comes from your records — it is not allowed to invent one. Requires iOS 26.
📲 Widgets, Siri & Shortcuts
Keep string status on your Home Screen or Lock Screen. Ask Siri to measure your strings, check a racquet, log a session, or open your history. Racquets show up in Spotlight too.
🔔 Reminders Worth Keeping On
Restring reminders, a tension-check interval, a baseline nudge after every restring, and a calibration prompt — all free and on by default. PRO adds target, streak, goal, recap, and budget alerts.
Physics, not guesswork
String Tension AI uses established acoustic physics — the same principles that govern musical instruments — to turn stringbed vibration information into a modeled current-tension estimate. All processing runs on-device. Your data stays private.
In plain English: When you tap your strings, the app listens for the stringbed response and turns it into a clear tension reading. Higher tension produces a different sound than lower tension, so you can track how your racquet changes over time without extra hardware.
Audio Capture
High-fidelity audio capture optimized for each iPhone model, with adaptive gain control and fine-grained timing analysis.
Impact Isolation
Signal isolation helps separate string taps from competing sound, while the Quality Coach warns when conditions may reduce measurement quality.
Frequency Analysis
Quality checks help separate clean string taps from background noise, so each reading is easier to trust and repeat.
Tension Calculation
The app produces a modeled current-tension estimate in lbs first, with kg shown second where useful, while accounting for your string type and racquet setup.
From club courts
to the pro circuit
Competitive Players
It's Saturday morning. League match in an hour. Your strings were done 10 days ago — are they still good? Take a measurement and compare the estimate with your saved baseline and threshold. If the trend has moved beyond your preferred range, grab your backup racquet.
Coaches & Academies
Your junior player keeps shanking forehands. Dead strings or bad technique? Check their racquet in 30 seconds. Manage your entire team's string health and send restring orders with exact tension specs.
Stringers & Technicians
Give your clients consistent tension tracking over time. Share measurement histories that show how each setup changes between string jobs. Build loyalty with a data-informed service that supports better restring conversations.
Trusted by players who
take their game seriously
"I had no idea my strings were losing 10% tension in the first week. Now I restring based on data, not guesswork. My consistency has improved noticeably."
"I coach 12 juniors. Being able to check their string tension in seconds — instead of guessing or sending them to the stringer — has been a game changer for match prep."
"My clients love getting tension reports after I string their racquets. It builds trust and they come back every time. Best tool I've added to my stringing service."
The 94% example is an illustrative signal and model quality indicator, not percentage accuracy versus a stringing machine.
Got questions?
How accurate is the tension measurement?
String Tension AI uses multi-stage acoustic analysis plus signal and quality checks to produce a modeled current-tension estimate. Calibration against a known reference can improve consistency when tracking the same setup over time. Profile tiers describe the basis for an estimate, while capture-confidence feedback reflects signal and model quality—not percentage accuracy versus a stringing machine. Read the evidence and limitations in our tension app accuracy guide.
Do I need any external hardware or accessories?
No. String Tension AI uses only your iPhone's built-in microphone. No Bluetooth devices, no clip-on sensors, no additional purchases. Just your iPhone and your racquet.
Does it work with all racquets and strings?
Yes. The app works with any standard tennis racquet and string combination. For best results, calibrate with your specific racquet and strings using a known reference tension. The app has 165 built-in string profiles across 21 brands and a catalog of 338 adult racquet models, so many players can skip manual setup entirely.
What does the Tension Advisor actually do?
The Tension Advisor analyzes your measurement history, playing patterns, court surface, weather conditions, and personal priorities (spin, comfort, power, etc.) to recommend the ideal tension for your next restring. It shows exactly why it's making each adjustment — transparent reasoning, not a black box. You can also explore "What If" scenarios to see how changing variables affects the recommendation.
Is my data synced across devices?
iCloud sync via CloudKit is a PRO feature. It keeps your measurements, racquets, string setups, and playing sessions synchronized across your Apple devices; sessions imported from Apple Health are deliberately left out and stay on the device. Local backups, a database export, and restore are free on every tier, and CSV and PDF reports are PRO. Health-sourced sessions are excluded from the exported archive too, so restoring it brings back everything except them.
How is this different from just asking my stringer?
Your stringer sets the reference tension when they string your racquet. Strings begin settling immediately, with polyester often changing fastest early in its life. String Tension AI helps you track what happens after stringing, between sessions, and over weeks.
Is it really free?
Yes. String Tension AI is free to download and free to use for measurements. There are no ads, no data selling, and no tricks. Advanced features like the Tension Advisor, decay forecast, cost analytics, exports, and iCloud sync are available with a PRO upgrade for serious players.
How long does a measurement take?
About 30 seconds from opening the app to seeing your tension reading. The app guides you through 3–10 taps and gives you results immediately. Most players measure before and after each match or practice session.
Can I use it in a noisy environment like a tennis club?
The Quality Coach monitors competing sound and tap quality, then guides you toward better conditions or rejects taps that do not meet quality checks. Quieter indoor conditions are generally easier; background noise can reduce measurement quality on courts and in clubs.
What does the free tier actually include?
Unlimited tap measurements with the Quality Coach and calibration, one racquet with one active string setup, your newest 20 readings on the chart and in history, fresh-string detection and baseline prompts, unlimited playing-session logging with goals and streaks, the reviewed Apple Health import, widgets, Siri Shortcuts, restring and tension-check reminders, seven of the eight visual share cards, and local backup, database export, and restore. Every reading you take is stored regardless of tier, so upgrading reveals the full history rather than starting it over.
Can the app import my tennis workouts from Apple Health?
Yes. The reviewed import pass is free: workouts arrive in an inbox where you keep or remove each one before it becomes a playing session. Automatic background import is a PRO feature. On both tiers, sessions sourced from Apple Health stay on the device: they are never pushed to iCloud, and they are left out of the backup archive you export and of CSV exports.
Are there widgets or Siri shortcuts?
Yes, and both are free. A String Status widget shows how a chosen racquet's strings are doing on the Home Screen in small, medium, and large sizes and on the Lock Screen in inline, circular, and rectangular forms. Siri phrases and App Shortcuts cover measuring string tension, checking racquet status, logging a playing session, and opening a racquet's history, and your racquets are indexed in Spotlight.
Stop guessing.
Start measuring.
Download String Tension AI and take your first measurement in under 30 seconds. Free to download. Free to measure. No accessories, no complicated setup, no catches.
iPhone · iOS 17+ · Free to download, free to measure.
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