dolfin, your indoor rowing companion.
A full-screen timer for indoor rowing workouts that runs entirely in the browser, built as a visual companion to the "Indoor Row" activity of modern smartwatches.
No backend, no build step, no dependencies:
dolfin is made by just static files
that can be simply copied behind a Web server like nginx.
Optionally, dolfin installs as a PWA and works offline.
A live example of dolfin can be found at https://www.albertopettarin.it/dolfin/
There are two screens: the Setup screen and the Workout screen.
It is split into four tabs: Programs, Intervals, Generic, and Customization.
The "Programs" tab lets the user pick one of the pre-defined workouts, plus optional warm up and cool down phases.
A program is one of two kinds: interval or generic.
An interval program is a block of effort and rest, repeated a number of times. The predefined interval programs are:
| Interval Programs | Description |
|---|---|
(01:30 + 00:30) x {5, 10, 15, 20, 30, 45, 60} |
(effort + rest) x repetitions |
(01:45 + 00:45) x {4, 6, 8, 12, 16, 18, 20, 24, 30, 32, 36, 48} |
|
(02:00 + 01:00) x {5, 10, 15, 20, 25, 30, 40} |
Tip
It is possible to define a custom interval workout, with parameters different than the predefined ones, in the Intervals tab.
A generic program is a workout written out phase by phase, in the very syntax the Generic tab takes.
Currently the predefined generic programs include the 8-weeks Beginner/Intermediate/Advanced training programs published by British Rowing.
Tip
It is possible to define a custom generic workout, with phases and parameters different than the predefined ones, in the Generic tab.
Press the Start button to transition to the Workout screen.
The "Intervals" tab lets the user set up a workout session made by repetitions of effort and rest phases, plus optional warm up and cool down phases.
Its default values are:
| Control | Default |
|---|---|
| Warm up time | 00:01:00 |
| Repetitions | 24 |
| Effort time | 00:01:45 |
| Rest time | 00:00:45 |
| Cool down time | 00:01:00 |
Time fields accept values in hh:mm:ss, mm:ss,
or plain integer number of seconds
(e.g., 00:01:42, 01:42 and 102 are all accepted).
A warm up, effort, rest, or cool down time of 00:00:00
simply skips that phase.
Press the Start button to transition to the Workout screen.
The "Generic" tab lets the user write out a workout that is not a plain repetition of the same effort and rest, plus optional warm up and cool down phases.
The plan is written one phase per line:
#: britishrowing.org
#: Advanced - Week 6 - Session 2
e: 02:00 @ 26-28 spm
r: 01:30
e: 01:00
...
| Line | Meaning |
|---|---|
#: britishrowing.org |
a comment, ignored |
e: 02:00 @ 20 spm |
an effort phase, two minutes long, labelled 20 spm |
r: 01:30 |
a rest phase, ninety seconds long |
e: 01:00 |
an effort phase, one minute long |
Times accept the same hh:mm:ss, mm:ss or plain-seconds forms
as every other time field, and must be greater than zero.
Blank lines and lines starting with # are ignored,
and e (effort) and r (rest) may be written in upper case.
Anything after an @ is a free-text label,
which is shown under the phase countdown.
Full examples, corresponding to the programs published by
British Rowing
and available in the Programs tab,
are located in the res/ directory.
If a line cannot be read, the Session total shows —,
and pressing Start reports the problematic line.
Press the Start button to transition to the Workout screen.
The "Customization" tab holds the preferences that apply to the Workout screen for all types of workout (programs, intervals, and generic):
| Control | Default |
|---|---|
| Allow skipping phase | True |
| Launch full screen | True |
| Progress panel | Small |
| Transition notice time (s) | 00:00:05 |
The Transition notice time setting represents how long before each phase ends the countdown starts blinking and the blips start. Set it to zero for no warning at all.
The five phase colours can be customized as well:
| Colour | Default |
|---|---|
| Warm up | #f2a63a (dark yellow) |
| Effort | #ff5c3d (light red) |
| Rest | #35b7ff (light blue) |
| Cool down | #2fd6a6 (light green) |
| Finished | #9ab0c6 (grey) |
The Reset colours button in that box restores the default colours, leaving the times, the workout plan and the chosen program alone.
The Reset button restores the default value for all controls.
Values are saved in localStorage,
so the next visit starts with the last values set
(possibly different than the default values).
The Workout screen cycles through the defined phases:
- interval workouts: warm up → ( (effort → rest) × repetitions ) → cool down → end of workout;
- generic workouts: warm up → ( phases as defined in the plan ) → cool down → end of workout.
Immediately below a screenshots of each phase:
A phase of a Generic workout that carries a label shows it under the countdown, on a line of its own:
The screen is split into two horizontal bands:
- the top band shows the current phase name (and the next one up), with a progress bar, a timer counting down the current phase, and the phase label, if it has one;
- the bottom band is the whole workout laid out end to end: one box per phase, each as wide a share of the screen as its duration is of the session, and in the colour of its phase. What is still to come is dimmed, so the edge between vivid and dim is where you are. Over it sit the current repetition / total repetitions, and below it the time remaining for completing the workout.
On the bottom right corner there are three buttons:
- Skip, shown only when the Allow skipping phase setting is selected, to skip the current phase and jump to the next one;
- Go Full Screen/Exit Full Screen to toggle the full screen mode;
- Stop to end the workout and go back to the setup screen.
Audio cues are synthesised short blips, one per second through the transition notice window at the end of every phase. A distinct tone plays when a phase starts: higher for effort, lower for everything else, and three descending tones at the end of the session.
While a workout is running:
| Action | Input |
|---|---|
| Pause / resume | click/tap anywhere, or press the Space key |
| Skip the current phase | click/tap the Skip button |
| Enter or leave full screen, session carrying on | click/tap the Go Full Screen / Exit Full Screen button |
| Stop the workout and go back to the Setup screen | click/tap the Stop button, or press the Esc key |
The screen is kept awake for the duration of the workout via the Screen Wake Lock API where the browser supports it, and the clock is anchored to wall time, so it does not drift if the tab is backgrounded.
Simply copy the dolfin/ directory into a location served by nginx.
Other Web servers (Apache, IIS, etc.) should "simply work" as well.
A live example can be found at https://www.albertopettarin.it/dolfin/
Note
A secure context is needed, that is, serve over HTTPS --- but, hey, it's 2026, you should use HTTPS always, everywhere, anyway!
cd dolfin
python3 -m http.server 8888or
make servethen open in your browser http://localhost:8888 .
Tip
localhost counts as a secure context,
so the service worker registers and offline mode can be tested there.
This project is licensed under the MIT License.
See the LICENSE file for details.
- Alberto Pettarin (Web)
Dolfin is the Venetian-dialect name for the iron comb on the bow of a gondola, the ferro di prua, whose six forward teeth stand for the six sestieri of Venice, while the single rear tooth stands for the Giudecca, and the arch above the top tooth is traditionally read as the Rialto bridge.
Note how the icon of the app is a stylized version of a dolfin, traced from a photograph of the real thing.
This project and its authors are not affiliated nor (unfortunately) endorsed or supported by Dolfin, the company producing the mythical Polaretti icicles.