Claymark — one tiebreak of clay-court tennis in a browser tab

01  What Claymark is

Claymark is a tennis game you open in a browser tab. There is one court — red clay, low sun, long shadows across the baseline — and exactly one format: a tiebreak, first to seven points, win by two. No sets, no tour, no career mode behind a menu. A match runs three to five minutes.

The court is drawn side-on, so you see its whole length at once: your player on the left, the opponent on the right, the net between them, the ball arcing over it. Before you touch anything a looping rally plays behind the title card, which is a fair way to see what the ball does before you are responsible for it.

It is free and ad-supported. There is no account, no install and nothing to download.

02  The serve is a timing test, and it is the hardest thing here

Every point starts the same way. Hold the Space bar — or the mouse button — to toss the ball, then release. A gold band on the serve indicator is the window: release inside it and you strike a clean serve, release early and the ball goes into the net, release late and it sails long.

The window is worth knowing exactly. The toss takes nine tenths of a second to peak, and the band opens about 0.56 seconds after you press and closes about 1.06 seconds in. So it is a half-second decision, and it stays open slightly past the top of the toss — "release at the peak" is close, but a fraction late still strikes clean.

Hold too long and the toss comes back down; releasing with the ball on the ground is an automatic fault, so you cannot wait it out. Two faults in a row is a double fault and the point goes to the opponent. The second serve is mechanically identical to the first — same band, same margins — so the discipline that keeps the first serve in is the discipline that keeps the point.

Serve alternates every point and you serve the first. Releasing later inside the band hits the ball harder, so the back half of the band is the aggressive serve.

03  You never steer the player — you choose the shot

You do not move your player around the court. While the opponent’s ball is in the air, your player runs himself toward the predicted landing point at a fixed 5.5 metres per second. What you own is when you swing and where you aim.

You can swing with a click or with Space, and only once the ball has bounced on your half — a ball still on the full cannot be hit. Let it bounce twice on your side and the point is gone, and the same is true at the other end.

Aim with the arrow keys: left and right set the width, up and down set the depth. Clicking on the court works too, and it aims at the point you click, because the mouse position is read while the button is held — click where you want the ball to land and that is where it goes.

Power is the interesting part, because there is no power bar to press. How hard you hit is decided by how well positioned your player is at the moment of contact: a ball you have to reach for comes back around 15 metres per second, a ball you are standing over comes off at the full 26. Since your player is running to the landing point for you, what actually decides your pace is whether the opponent managed to pull him wide. The shots that hurt you are the ones that make you hit on the move.

04  Spin, drag, and a clay bounce that grabs

The ball is not following a drawn curve. It is integrated forward sixty times a second under gravity, quadratic air drag and the Magnus force that spin generates, with real constants — a 57.7 gram ball, a 33.5 millimetre radius, a drag coefficient of 0.55 — kept in one tuning file rather than scattered through the code.

Clay is modelled as its own surface, which matters more than it sounds. A ball landing on clay keeps 75% of the speed it came down with, where a hard court keeps about 85%, and the surface takes 35% of the horizontal speed off the ball on every bounce. Clay grabs, and the ball sits up. Topspin converts into forward kick off the bounce, so a heavy topspin ball accelerates away instead of checking; slice converts into a sideways skid.

Where spin actually comes from today: the TOPSPIN and SLICE buttons under the court on a touch device, with flat as the default when neither is lit. There is no spin control on the desktop build, so on a keyboard your rally shots come out flat. If you want to play with heavy topspin, this is currently a phone or tablet game — better to say so plainly than to have you find out after ten minutes.

05  Three opponents, defined by three numbers

You pick the opponent on the results screen and the choice is remembered for the next match. Casual, Standard and Sharp are not three different scripts; each is a row of numbers.

Reaction delay — how long the opponent waits after your shot before moving — is 0.3 of a second on Casual, 0.18 on Standard, a tenth of a second on Sharp. Top speed goes 5.2, 6.5, 8.5 metres per second. The error radius, which is how far off their read of your shot can be, is 1.15 metres, 0.8, then 0.45. Sharp gets moving a third of a second sooner, covers ground half again as fast, and lands within half a metre of where it means to. That combination is what makes wide angles stop being winners.

There is a real lever against the harder tiers, and it is in the numbers. The opponent’s aiming error is not fixed — it grows with the pace of your shot and with how wide you hit it, because it is applied to their prediction of where your ball will land. A hard, wide ball does not only beat them for speed; it enlarges the error in their read. That makes the wide heavy ball the shot that breaks a Sharp opponent, and safe central balls the thing that lets one settle.

Where they aim is weighted by distance from you — court zones far from where you are standing are likelier targets — with enough randomness that they can still be wrong-footed.

06  The court remembers, and the mark map

Every bounce leaves a mark. Fresh marks are lighter than the surface, disturbed clay catching the light, and they darken and fade over about five seconds; the renderer keeps the most recent hundred and twenty on screen while the sim records up to two hundred contacts a match. By match point the clay behind the baseline is visibly scarred, and the scars are the record of where this particular rally went.

At the end you get the mark map: a top-down image of the court showing every contact from the match, with the score and your longest rally on it. It is generated from the shots you actually hit, so no two matches produce the same picture, and there is a share button next to rematch that copies a link to it.

The results screen also offers a handle — two words drawn from a word list, five options at a time, rerollable — and submits your longest rally to a daily board, but only if it beats your personal best from that browser. The board is keyed to the day in UTC and keeps the top ten. Nothing you type leaves the browser, which is easy to guarantee because there is nothing to type.

One honest caveat: the number on that board comes from your own browser and nobody verifies it. Treat it as a scoreboard of claims rather than a ranking.

07  Questions people ask

Is Claymark free, and do I need an account?

Free and ad-supported, with no account, no sign-up and nothing to install. Your chosen difficulty, your handle and your personal-best rally are kept in your own browser.

Do I need a keyboard, or can I play it on a phone?

It is built for a keyboard: Space to toss and to swing, arrow keys to aim, clicking on the court to place a shot. On a touch device you get drag-to-aim and two spin buttons under the court instead, and the serve is a hold-and-release anywhere on the screen.

How long does a match take?

One tiebreak, first to seven points, win by two. Most matches are done in three to five minutes; a close one that runs to 8-6 or 9-7 takes longer. Rematch is one keypress from the results screen.

What is the mark map?

A top-down image of the court showing every bounce and hit from the match you just played, with the score and your longest rally. It is generated from the shots you actually hit, not a stock illustration, and it can be shared as a link.

Does the AI opponent cheat?

No. It plays through the same ball physics you do, limited by three numbers: how long it waits before reacting, how fast it can run, and how badly it can misread where your shot is going. It does not teleport and it cannot see the future — the error in its read is the thing you are playing against.

08  More from the shelf

• Fiveaside — Score past the keeper. Post the scoreline.
• Acecourt — Nail the timing. Serve the ace.
• Oche — One board. Three darts. Finish on a double.
• Dewkeep — Keep a creature. Grow a little world.

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