The Quest for the Perfect Terminal Emulator — Personal Testing Notes on Latency and Font Rendering Across Alacritty, Foot, and Kitty

Introduction

As a Linux user, one of the most frequent applications I interact with is my terminal emulator. It's my window into the system, a space for coding, debugging, and managing tasks. For years, I've been trying to find the perfect terminal emulator—one that strikes a balance between speed, aesthetics, and usability. In this blog post, I'll walk through my testing of three terminal emulators that have gained a lot of attention in the Linux community: Alacritty, Foot, and Kitty.

The focus of this evaluation is on two critical aspects: latency and font rendering. Both are important for providing a smooth and enjoyable experience, whether I'm running simple commands, working with high-output processes, or navigating directories.

1. Latency: The Race for Responsiveness

What is Latency in a Terminal?

When using a terminal emulator, latency refers to the time between pressing a key and seeing the result on-screen. This delay can be noticeable when typing fast or running commands that generate a lot of output. For developers, sysadmins, and anyone who spends a significant amount of time in the terminal, lower latency is essential for a fluid experience.

Testing Setup

To test latency, I performed a series of subjective tests by typing at my normal speed, observing how quickly each terminal reacted to keystrokes. I also ran several long-running commands (such as find /, git status, and others) to see how quickly the terminal could update with new output.

• Hardware: Intel i7 CPU, 16GB of RAM, NVMe SSD
• OS: Arch Linux (with Wayland as the compositor)
• Graphics: NVIDIA GPU with proprietary drivers

Alacritty

Alacritty is widely praised for its low latency, and for good reason. It's built with GPU acceleration in mind, leveraging OpenGL to render text and handle graphics. This allows it to provide extremely responsive performance with minimal delay.

• Performance: Alacritty felt snappy, even when running large commands. The GPU rendering ensured that text appeared almost immediately after a key was pressed.
• Key Event Handling: Keystroke registration felt instant, with no noticeable lag, even when multiple characters were typed in rapid succession.

Foot

Foot, a Wayland-native terminal emulator built with simplicity and performance in mind, also has impressive latency characteristics. It's not as feature-rich as Alacritty, but its minimalism aids performance.

• Performance: Foot performed quite well with low latency, but it wasn't quite as responsive as Alacritty. The focus here seems to be on minimalism, and it shows in its lightweight nature. Still, typing felt smooth and almost immediate.
• Key Event Handling: Slightly slower than Alacritty, but only in scenarios with very high throughput, like piping multiple outputs.

Kitty

Kitty, like Alacritty, uses GPU rendering for performance but also includes several more features, such as image display and advanced font rendering options.

• Performance: Kitty had a solid performance profile, though it was slightly behind Alacritty in terms of raw latency. The extra features come at the cost of a marginal increase in responsiveness.
• Key Event Handling: Typing was responsive, but it showed a slight delay when running commands that produce a large amount of output (e.g., ls -lR /).

Conclusion on Latency

• Best Overall: Alacritty wins for the lowest latency, consistently outperforming both Foot and Kitty. Its reliance on GPU acceleration for rendering ensures smooth performance, even under heavy workloads.
• Runner-Up: Foot is highly responsive and lightweight but falls slightly behind Alacritty when handling fast typing.
• Third Place: Kitty provides good performance but sacrifices some latency in favor of advanced features.

2. Font Rendering: Crisp, Clean, and Easy on the Eyes

Why is Font Rendering Important?

Font rendering is crucial for readability and comfort, especially if you're spending long hours in the terminal. The way fonts are rendered can affect text sharpness, weight, and clarity. Poor font rendering can strain your eyes and reduce productivity.

Testing Setup for Font Rendering

I tested font rendering by evaluating the clarity of both default and custom fonts across various font sizes. For consistency, I used the FiraCode font in all three terminals, though I also tested with Hack and Source Code Pro for variety.

• Screen Resolution: 1920x1080p
• Font Sizes: 12px, 14px, and 16px
• Anti-Aliasing: Enabled for all terminals, with subpixel rendering enabled where supported.

Alacritty

Alacritty uses GPU-based rendering to display text, which gives it an edge in font clarity. Fonts are sharp and well-defined, especially at smaller sizes.

• Rendering Quality: Text is extremely crisp, and even at 12px, there’s no noticeable pixelation. Anti-aliasing is smooth, and the text appears well-optimized for readability.
• Customization: Alacritty supports font ligatures and provides excellent control over font settings (such as weight, style, and line height). The configuration file is straightforward to tweak for any font preferences.

Foot

Foot’s minimalism extends to its font rendering, which, while decent, isn’t as polished as Alacritty. The fonts are clear and readable but lack the crispness that Alacritty’s GPU rendering provides.

• Rendering Quality: Font rendering is solid but not as fine-tuned. There’s a slight blur around the edges of characters at smaller sizes, but it's still perfectly usable.
• Customization: Foot has basic support for font customization, but the options are more limited compared to Alacritty.

Kitty

Kitty provides excellent font rendering with support for multiple font types and ligatures, alongside advanced anti-aliasing and subpixel rendering.

• Rendering Quality: Fonts are very sharp, and the text rendering is as good as or better than Alacritty in terms of aesthetics. The advanced anti-aliasing settings and subpixel rendering make it a standout in visual quality.
• Customization: Kitty excels here, offering advanced font options like variable fonts, multi-font rendering, and extensive font-related settings in its configuration file.

Conclusion on Font Rendering

• Best Overall: Kitty takes the top spot for font rendering, offering the most aesthetically pleasing output and the greatest range of font customization options.
• Runner-Up: Alacritty offers exceptional performance but falls just short of Kitty in terms of visual quality and customization.
• Third Place: Foot offers functional font rendering but doesn't have the same level of crispness or customization as the other two.

Final Thoughts

After testing Alacritty, Foot, and Kitty over the course of several months, it’s clear that each terminal excels in different areas. Alacritty stands out for its sheer speed and low latency, making it the best choice for those who prioritize responsiveness. Kitty, on the other hand, offers unparalleled font rendering and a feature-rich experience, making it ideal for those who want the best visual quality and extensive customization. Foot may not be as feature-packed, but its simplicity and performance make it a great choice for those seeking a minimal and lightweight terminal experience.

Ultimately, the "perfect" terminal emulator depends on what you prioritize. If raw performance and latency are your top concern, Alacritty is hard to beat. However, for a balance of aesthetics, customization, and usability, Kitty is likely the best option.

In the end, experimenting with these options has been a rewarding experience, and I encourage others to test these emulators for themselves to see which one best fits their workflow. The pursuit of the "perfect" terminal may never truly end, but with these three contenders, it's clear we're getting closer.