Search "free tennis shot detection app" and most of what comes back is not shot detection. You get watch apps that count swings from your wrist, replay tools that mirror your video in slow motion, and freemium apps whose free tier expires the week you start caring. Very few do the thing the phrase actually describes: watch your match, find every ball you hit, and label each one. Forehand. Backhand. Serve. Volley.
I run AceSense, so this post includes us. It is also the post I wish existed before we built our free tier, because the word "free" here hides at least three different products, and only one of them is automatic shot detection you can keep using without paying.
If you want the straight app-by-app comparison of free tiers, I wrote that separately in the best free tennis stat tracker roundup. This post is narrower: only detection, the labelling step, and what "free" means for that one capability.
What shot detection actually is
Shot detection is one specific job: find the moment of contact in the video and attach a label to it. Not a count you tapped in yourself. Not a swing your watch felt. A per-shot label the software produced by looking at the footage, this frame is a forehand, that one is a serve, this one is a volley.
That distinction is the whole post, so it is worth being blunt about it. Three things get sold as free tennis analysis, and only the third is detection.
- Counting is not detection. A wrist tracker feels an acceleration spike and adds one to a tally. It can tell you that you swung roughly 180 times. It cannot tell you which of those were backhands, or where the ball landed, because it never saw the ball or the court.
- Tagging is not detection. Some free apps let you scrub the video and tap a button every time you hit a shot. That is manual labelling with extra steps. You are the detector; the app is a spreadsheet with a video player bolted on.
- Detection is the software doing the labelling for you, automatically, from the pixels. That is the part that is genuinely hard, genuinely expensive to run, and genuinely rare at €0.
Every downstream feature you actually want sits on top of that labelling step. The court heatmap, the shot-mix counts, the stroke-quality scores, none of them exist until detection has found and named the shots first (the full argument is on the shot detection feature page). The point here is simpler: if an app is not doing that labelling automatically, it is not a shot detection app, however it is marketed.
The three flavours of 'free' that are not free detection
When you filter the search results through that definition, most of them fall into one of three buckets.
1. The trial in disguise. These are the freemium video apps whose free tier exists to get you to the upgrade prompt. The category pattern is a capped free tier: limited match recording, watermarked exports, gated analytics. SwingVision's free tier fits that shape as of this writing, per its published tier descriptions. As the roundup covers in detail, a tier like that is functionally a demo rather than a long-term tool. Nothing wrong with a demo. It is just not free detection you can rely on every week.
2. The replay mirror. This is the Coach's Eye lineage: slow-motion review, frame-by-frame scrubbing, a delayed mirror of your own video. Useful for watching your form, genuinely, but there is no detection happening. Nothing finds your shots or labels them. These tools are easy to build and, it turns out, easy to switch off. Coach's Eye was shut down by TechSmith, and the players who used it for tennis slow-motion had to go find something else.
3. The wrist counter. TennisKeeper and Swing both have free tiers that count shots and estimate swing speed from an Apple Watch. That is genuinely free and genuinely useful if a shot count is all you want. But it is watch-sensor counting, not video detection. There is no per-shot label derived from footage, no court map, no read on where the ball went. It answers "how many" and stops there.
None of these are scams. They are just different products wearing the same search term. What none of them does is the thing the phrase promises: automatically find and label your shots from video, for free.
What a genuinely free detection tier looks like
Here is the AceSense free tier, stated plainly so you can hold it against anything else you are considering:
- €0 per month. No credit card to start.
- 3 match analyses per month. Enough for about one match a week with an off week.
- The full report, not a stripped one. Shot detection, ball tracking, court heatmap, and stroke-quality scores, with no watermarks and no feature gates.
- 30-day report history.
- iOS and Android.
The part that matters most for this post: the detection on the free tier is the exact same model the paid tiers run. Same pipeline, same accuracy. There is no "more accurate detection" hiding behind the paywall. The free tier is rate-limited, not feature-limited. What Pro (€19/month) and Team (€49/month) unlock is volume and coaching-team features, not a better detector. The full breakdown is on the pricing page.
That is deliberate. We would rather you test real detection on your own matches and decide, than hand you a hobbled free version that makes the paid one look good.
The honest limits of free detection
Free automatic detection is real, but it is not unconstrained. If a vendor tells you it is, that is the tell. Three limits are worth knowing before you rely on it.
The monthly cap is the price of the GPU bill. Every match you analyse runs a chain of models on a GPU: ball tracking, court keypoints, pose extraction, and the classifier that labels each shot. A 60-minute match is 3 to 5 minutes of GPU time, somewhere around 8 to 30 cents in raw cloud cost. Three a month is where the free-tier maths works without an upgrade trap or an ad wall. Anyone offering unlimited free detection is running a loss leader, a lighter on-device heuristic that is not really pose-aware, or a product on borrowed time.
It is post-match, not real-time. You upload after you play, the pipeline runs in the cloud, and the report comes back in minutes. By the time you have driven home, the whole match has been processed shot by shot. What it is not is live line-calling during the point. That is a different, harder problem, and not what a free detection tier is for.
The camera does a lot of the work. Detection is only as good as the video you feed it. The pipeline assumes a stationary camera, at least 5 feet up, behind the baseline, filming in landscape with the whole court in frame, using your phone's main lens rather than the ultrawide, at 30fps or higher. Get that right and the numbers below apply to your footage. Film hand-held at hip height with half the court cut off and they do not. The filming guide is worth reading before your first upload, not after a disappointing report.
How to check a 'free detection' claim before you trust it
This is the section I would keep if you skip the rest. Most apps describe accuracy with adjectives, "best-in-class," "professional grade," "highly accurate," and none of those are measurements. Here is the rule that cuts through it.
Published F1, or it did not happen.
F1 combines precision (of the shots it flagged, how many were real) and recall (of the shots that happened, how many it caught) into one number, where higher means the model both finds real shots and does not invent ones that were not hit. A vendor who has measured their detection can show you that number. One that has not, cannot.
Ask three questions of any "free detection" app:
- Is there a number, or only an adjective?
- Is the method behind the number described, the dataset, how it was measured, what was held out?
- Are the failure modes listed, or is everything presented as flawless?
If all three come back empty, "detection" is a marketing word on that app, not a capability you can size. AceSense publishes shot-detection F1 by shot type, the dataset it sits on, and the specific failure modes, on the accuracy page, and updates it every release. That is the bar to hold everyone to, us included.
Which shots get detected, and how well
Detection covers forehand, backhand, serve, and volley, plus overhead and slice as subtypes. From the current published build on the accuracy page, the per-shot F1 scores are:
| Shot | F1 |
|---|---|
| Forehand | ~ 0.92 |
| Backhand | ~ 0.91 |
| Serve | ~ 0.88 |
| Slice | ~ 0.83 |
| Volley | ~ 0.78 |
In plain terms: on a 90-shot match, expect roughly 80 to 85 shots correctly detected and classified, 3 to 5 misclassifications (most often slice mistaken for backhand, or a volley at the service line mistaken for a groundstroke), and 0 to 2 shots missed entirely. Forehands and backhands are the most reliable; volleys are the hardest, and overheads get pulled toward "serve" at low camera angles. Those rates are tight enough that the coaching insights, your shot mix and where your leak actually is, hold up. They are not tight enough to run a match on, and we say so.
These numbers move each release, which is the point of publishing them. For the pipeline behind them, how AI tennis shot detection works is the long version.
Which free option fits which player
"Free" is not one decision. It depends on what you actually need detection for.
- You just want a shot count and social bragging rights. You do not need detection. A free wrist tracker will tell you how many forehands you hit and roughly how fast you swung, and that is enough. Save the analysis for when you have a specific problem to solve.
- You are an improving club player (NTRP 3.0–4.5) who wants to know your real shot mix and where points leak. This is exactly what automatic detection is for, and the free tier's 3 analyses per month fits the cadence. One match a week, analysed properly, beats ten watched on vibes.
- You are on Android. Your options collapse fast. Most watch trackers and several video apps are Apple-only, so a genuinely free automatic detection tier that runs on Android is close to a category of one.
- You are a coach or you film most days. The free cap will not hold you. Use it to confirm the detection is real on your own footage, then move to Pro (€19/month, unlimited) or Team (€49/month, 10 seats). Same detector; you pay for volume, not accuracy.
- You are not sure AI detection is worth anything. Then the no-card free tier is the whole point. Run it on one real match and judge the labels yourself, rather than trusting my claims or a competitor's adjectives.
FAQ
Is there a genuinely free tennis shot detection app? Yes, but few. AceSense's free tier does automatic detection for €0, no card, 3 analyses a month, on iOS and Android. Most other "free" options are trials, replay tools, or wrist counters.
Why is free detection capped instead of unlimited? GPU cost. A 60-minute match is 3 to 5 minutes of GPU time, roughly 8 to 30 cents. Three a month is where free works without an upgrade trap. "Unlimited free" usually hides an ad wall, a heuristic, or a shutdown.
How accurate is the detection? Per-shot F1 on the current published build is about 0.92 forehand, 0.91 backhand, 0.88 serve, 0.83 slice, 0.78 volley. Full method and failure modes are on the accuracy page.
How do I know a vendor's detection claim is real? Published F1, or it did not happen. Look for a number, a described method, and a list of failure modes. Adjectives are not measurements.
Try it on your own match. Start free, 3 full per-shot reports a month, no card. Then read how detection works, check the accuracy numbers before you trust them, or see the free-tier roundup for the app-by-app comparison.