Catime: a 995KB pure C timer for the Windows tray

What Catime actually replaces on a Windows desktop

Most timers on Windows are either a browser tab, a phone app, or a heavyweight Electron window that idles at a few hundred megabytes. Catime takes the opposite position: it is a native Windows program written in C, and the README describes it as an "ultra-lightweight Windows countdown and Pomodoro tool" that fits in 995KB. The feature set is the ordinary one you would expect from a kitchen timer, expanded: clock, countdown, stopwatch, Pomodoro, plus tray animations that can be a GIF, WebP, ANI, PNG or JPG, or a live readout of CPU percentage, memory percentage, battery percentage and Caps Lock state.

The audience is narrow and specific. It is for Windows users who keep a timer visible all day and do not want a window for it. The transparent overlay and the tray icon are the two surfaces, and the README's user guide reduces the interaction model to two gestures: left-click the tray icon to set a time, right-click to open the menu. If you work primarily on Linux or macOS, this is the wrong tool, and nothing in the repository suggests a port is planned.

How the timer, the tray icon and the plugin channel fit together

The architecture visible in the repository is a small C program with a CMake build, a mingw-w64 toolchain file, an include directory, a src directory, a libs directory and an i18n directory. Configuration is not stored in the registry or in a hidden database; the README states it is saved at %LOCALAPPDATA%\Catime\config.ini, which means the whole state of the application is a text file you can back up, diff or edit by hand.

The plugin mechanism is the most interesting design decision, and also the most minimal. The README says plugins "simply write their output to ./output.txt, and Catime displays it in real time". There is no plugin API, no SDK, no loading of shared libraries. A separate process writes a file, and Catime polls or watches that file and renders its contents. That is a deliberate trade-off: it makes a plugin possible in any language, including a shell script, but it also means the integration surface is one file path and no structured data. Anything richer than a line of text has to be encoded by the plugin author.

The tray animation path is separate from the plugin path. Animated icons come from image files the user supplies, while the system status modes read CPU, memory, battery and Caps Lock directly. The README does not document how often those values are sampled, so the refresh rate is not something you can plan around from the documentation alone.

Installing Catime and running a first Pomodoro

Catime is distributed three ways. The README points to the Microsoft Store listing, to GitHub Releases for the latest build, and to two package managers. On Windows with winget available, the install is one line. The README gives this exact command.

winget install --id VladElaina.Catime

After it completes, Catime should appear in the notification area. Left-clicking the tray icon is how you set a time, per the user guide; right-clicking opens the menu where the countdown, stopwatch and Pomodoro modes live.

If you prefer Scoop, the README lists a bucket add followed by the install, and the bucket is extras.

scoop bucket add extras
scoop install catime

The third route is downloading the latest release asset directly from GitHub Releases, which is what you want if neither package manager is present.

Once running, the settings you change through the menu land in the configuration file. The README gives the path.

%LOCALAPPDATA%\Catime\config.ini

Opening that file is the fastest way to confirm that a change actually persisted, and it is also where you would keep a copy if you move between machines. For a custom font, the README recommends the official Font Simplification Tool, which it says reduces a custom font file by more than 90 percent, because Catime only renders the digits 0-9 and the characters : and . The README also advises keeping the original font file as a backup, since future updates may need characters outside that set.

Where Catime stops being the right choice

The platform restriction is the first limitation and it is not a small one. The README describes Catime as a Windows tool, the build instructions target MinGW and CMake for a Windows binary, and the install paths are winget, Scoop and a Windows release asset. If your team is mixed-platform, Catime solves the problem for one subset of it and leaves the rest with whatever they were using before.

The second limitation is the plugin contract. Writing output to ./output.txt is easy to implement and easy to explain, but it gives you no schema, no error channel and no way to express anything beyond what fits in a text file. A plugin that needs to report a structured state, or that needs Catime to send something back, has nowhere to put that. The README points to a companion repository, Catime-Plugins, for ready-made examples rather than documenting a specification, so the practical answer to "what can a plugin do" depends on reading those examples.

The third is documentation depth. The README covers installation, the two tray gestures, the config path and the font tool. It does not document the config.ini keys, the sampling interval for CPU and memory readouts, or how the Pomodoro mode behaves when a session is interrupted. Those are things you find by using the program, not by reading about it.

Catime against a general-purpose Pomodoro app

The obvious alternative is a cross-platform Pomodoro application, typically built on Electron or a similar runtime, that runs on Windows, macOS and Linux from one installer. The difference in approach is not cosmetic. A cross-platform app trades binary size and idle memory for reach: one tool for everyone on the team, one set of documentation, one release cadence. Catime trades reach for footprint, staying at 995KB and, in the README's phrasing, at "negligible resource consumption".

That trade changes who the tool is for. If your reason for running a timer is that you want it on the same screen as your editor with a transparent overlay, and you never leave Windows, Catime's model is a better fit than a windowed app you have to position. If your reason is that you want the same timer on a work laptop and a personal Mac, a cross-platform app wins by default, because Catime has no build for that second machine.

A second comparison point is the tray animation feature itself. A general-purpose Pomodoro app usually shows a static icon and a notification. Catime lets the icon be a GIF or a live CPU and memory readout, which is a different product decision: the tray icon becomes a small status display rather than a mode indicator. That is genuinely useful if you already watch system load, and irrelevant if you do not.

Maintenance, licence and the cost of upgrading

Catime is not archived, and the last push to the default branch was on 2026-09-21, two days before this writing. The release history shows v1.5.0 on 2026-07-09, v1.6.0 on 2026-08-23 and v1.6.2 on 2026-08-27, so the project is shipping on a roughly monthly cadence through the summer of 2026. That cadence is the main upgrade cost: if you pin a version, expect to revisit it periodically to pick up fixes.

The practical upgrade burden is low because there is no server component and no database. The state is config.ini under %LOCALAPPDATA%\Catime, so an upgrade is replacing a binary and keeping that file. The one caveat the README itself raises is fonts: it warns that future software updates may require characters beyond the current set of 0-9, : and ., which is why it recommends keeping the original font file as a backup. If you have run a font through the Font Simplification Tool and discarded the source, a later release could leave you with missing glyphs.

The licence is Apache-2.0, which permits commercial and private use, modification and redistribution, and includes an explicit patent grant. Apache-2.0 also requires that you preserve copyright and licence notices and state significant changes when you redistribute a modified version. If you simply install and use Catime, none of those obligations are triggered. If you plan to bundle a modified Catime into a product, read the licence text in the repository's LICENSE file rather than relying on a summary; this is not legal advice.

Editorial conclusion

Adopt Catime if you work on Windows and want a countdown or Pomodoro that lives in the notification area, costs almost nothing in memory, and can be driven by tray clicks and shortcuts. Skip it if you need Linux or macOS support, or if your workflow depends on a plugin ecosystem that is already mature; the plugin model here is a single ./output.txt file and the companion Catime-Plugins repository. Before you commit, install it with winget install --id VladElaina.Catime, open %LOCALAPPDATA%\Catime\config.ini and confirm the settings you care about are actually exposed there, and test your custom font with the Font Simplification Tool before you delete the original file.

Frequently asked questions

Official sources

1. License: Apache-2.0
2. Project website
3. README
4. Releases
5. vladelaina/Catime on GitHub