634957c8e6
This is a series of seven commits that optimizes VT processing throughput. Each commit is isolated, individually benchmarked, and carries a detailed commit message so please read each for details about each change. Whereas #13220 was driven by synthetic data, this series was driven by profiling a 2.6 GB recording of real terminal sessions from an asciinema data dump. Through this, I've been able to improve throughput processing the full dump from 276 to 342 MB/s on my system. > [!NOTE] > > **LLM usage:** This series of work was largely driven by Fable 5 and the summaries below started as LLM-written. I've proofread (and mostly modified) every line of work and rewritten everything to be shorter and more in line with how I'd describe a change. Nothing here was unreviewed. I also threw away 3 sets of changes I didn't agree with the maintenance of, but did speed up things a bit. ## The changes 1. **decode ASCII inline in the SIMD scan for ESC**. Real streams call `utf8DecodeUntilControlSeq` on short runs (an escape every ~18 bytes), so ~9% of total time was simdutf setup plus its scalar tail paid per tiny run. The ESC scan and the UTF-8 to UTF-32 "decode" (a widening for ASCII) are now one pass. **Result: +5.4% on the real corpus.** 2. **handle CSI entry bytes inline in consumeUntilGround**. The `[` after ESC and the single `csi_entry` byte each paid a `nextNonUtf8` call, two to three calls for every one of the tens of millions of CSI sequences in the recording. Both transitions are now handled in the consumeUntilGround loop, so a typical CSI parses with no per-byte calls at all. **Result: +2.7% real corpus, +3.1% CSI-heavy stream.** 3. **fill style-only cell runs in bulk in printSliceFill**. The largest single item in the profile (~25%). The print fast path's two scans (run eligibility, simple-cell check) are early-exit search loops LLVM won't vectorize, and real traffic constantly lands in the general path because styled text overwrites cells styled differently (TUI redraws), paying a per-cell release/use pair. The scans are now vectorized and uniformly-styled runs are consumed wholesale: one vector scan, one releaseMultiple/useMultiple pair, one branch-free fill. **Result: +11% real corpus, +21% TUI redraw.** 4. **release style refs per run instead of per cell in clearCells**. Erasing styled rows released each cell's style reference one at a time even though styled cells overwhelmingly share one style per run (status bars, highlighted regions, solid rows). Runs now release with a single releaseMultiple. **Result: +1.1% real corpus, 2.1x on full-screen styled erase.** 5. **log unsupported-input messages once per distinct value**. The recording triggers ~120k warnings, dominated by a few messages some program re-emitted every frame ("unimplemented mode: 34"), each paying formatting plus a blocking writev while adding nothing beyond the first occurrence. A logUnsupportedOnce helper suppresses repeats per (call site, value) using a 64-byte lock-free table per site. **Result: +3.2% on the real corpus, system time halved.** ## Benchmarks Measured with `ghostty-bench +terminal-stream` (full terminal handler, 120x80 terminal, M4 Max, macOS 26, ReleaseFast, hyperfine means of 6 runs, 64KiB read chunks). These are parser-stage numbers, not end-to-end app numbers. | stream | before | after | throughput | change | |-------------------------------|---------|---------|------------------|--------| | real 2.6 GB session recording | 9.441 s | 7.609 s | 276 → 342 MB/s | 1.24x | | ascii (no escapes) | 119 ms | 84 ms | 838 → 1186 MB/s | 1.41x | | TUI redraw (rotating styles) | 417 ms | 293 ms | 240 → 342 MB/s | 1.42x | | styled paint + ED 2 erase | 418 ms | 124 ms | 239 → 808 MB/s | 3.38x | | csi mix (random-color SGR/CUP)| 695 ms | 696 ms | (adversarial) | ~1.0x | Note the "csi mix" benchmark above was a generated adversarial input e.g. a worst-case input for the changes we made. It wasn't based in real-world data or expectations. But I asked for it to be done so we can verify we don't see regressions too much (and were able to verify we see basically none).
Ghostty
Fast, native, feature-rich terminal emulator pushing modern features.
A native GUI or embeddable library via libghostty.
About
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Download
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Documentation
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Contributing
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Developing
About
Ghostty is a terminal emulator that differentiates itself by being fast, feature-rich, and native. While there are many excellent terminal emulators available, they all force you to choose between speed, features, or native UIs. Ghostty provides all three.
libghostty is a cross-platform, zero-dependency C and Zig library
for building terminal emulators or utilizing terminal functionality
(such as style parsing). Anyone can use libghostty to build a terminal
emulator or embed a terminal into their own applications. See
Ghostling for a minimal complete project
example or the examples directory
for smaller examples of using libghostty in C and Zig.
For more details, see About Ghostty.
Download
See the download page on the Ghostty website.
Documentation
See the documentation on the Ghostty website.
Contributing and Developing
If you have any ideas, issues, etc. regarding Ghostty, or would like to contribute to Ghostty through pull requests, please check out our "Contributing to Ghostty" document. Those who would like to get involved with Ghostty's development as well should also read the "Developing Ghostty" document for more technical details.
Roadmap and Status
Ghostty is stable and in use by millions of people and machines daily.
The high-level ambitious plan for the project, in order:
| # | Step | Status |
|---|---|---|
| 1 | Standards-compliant terminal emulation | ✅ |
| 2 | Competitive performance | ✅ |
| 3 | Rich windowing features -- multi-window, tabbing, panes | ✅ |
| 4 | Native Platform Experiences | ✅ |
| 5 | Cross-platform libghostty for Embeddable Terminals |
✅ |
| 6 | Ghostty-only Terminal Control Sequences | ❌ |
Additional details for each step in the big roadmap below:
Standards-Compliant Terminal Emulation
Ghostty implements all of the regularly used control sequences and can run every mainstream terminal program without issue. For legacy sequences, we've done a comprehensive xterm audit comparing Ghostty's behavior to xterm and building a set of conformance test cases.
In addition to legacy sequences (what you'd call real "terminal" emulation), Ghostty also supports more modern sequences than almost any other terminal emulator. These features include things like the Kitty graphics protocol, Kitty image protocol, clipboard sequences, synchronized rendering, light/dark mode notifications, and many, many more.
We believe Ghostty is one of the most compliant and feature-rich terminal emulators available.
Terminal behavior is partially a de jure standard (i.e. ECMA-48) but mostly a de facto standard as defined by popular terminal emulators worldwide. Ghostty takes the approach that our behavior is defined by (1) standards, if available, (2) xterm, if the feature exists, (3) other popular terminals, in that order. This defines what the Ghostty project views as a "standard."
Competitive Performance
Ghostty is generally in the same performance category as the other highest performing terminal emulators.
"The same performance category" means that Ghostty is much faster than traditional or "slow" terminals and is within an unnoticeable margin of the well-known "fast" terminals. For example, Ghostty and Alacritty are usually within a few percentage points of each other on various benchmarks, but are both something like 100x faster than Terminal.app and iTerm. However, Ghostty is much more feature rich than Alacritty and has a much more native app experience.
This performance is achieved through high-level architectural decisions and low-level optimizations. At a high-level, Ghostty has a multi-threaded architecture with a dedicated read thread, write thread, and render thread per terminal. Our renderer uses OpenGL on Linux and Metal on macOS. Our read thread has a heavily optimized terminal parser that leverages CPU-specific SIMD instructions. Etc.
Rich Windowing Features
The Mac and Linux (build with GTK) apps support multi-window, tabbing, and splits with additional features such as tab renaming, coloring, etc. These features allow for a higher degree of organization and customization than single-window terminals.
Native Platform Experiences
Ghostty is a cross-platform terminal emulator but we don't aim for a least-common-denominator experience. There is a large, shared core written in Zig but we do a lot of platform-native things:
- The macOS app is a true SwiftUI-based application with all the things you would expect such as real windowing, menu bars, a settings GUI, etc.
- macOS uses a true Metal renderer with CoreText for font discovery.
- macOS supports AppleScript, Apple Shortcuts (AppIntents), etc.
- The Linux app is built with GTK.
- The Linux app integrates deeply with systemd if available for things like always-on, new windows in a single instance, cgroup isolation, etc.
Our goal with Ghostty is for users of whatever platform they run Ghostty on to think that Ghostty was built for their platform first and maybe even exclusively. We want Ghostty to feel like a native app on every platform, for the best definition of "native" on each platform.
Cross-platform libghostty for Embeddable Terminals
In addition to being a standalone terminal emulator, Ghostty is a
C-compatible library for embedding a fast, feature-rich terminal emulator
in any 3rd party project. This library is called libghostty.
Due to the scope of this project, we're breaking libghostty down into
separate libraries, starting with libghostty-vt. The goal of
this project is to focus on parsing terminal sequences and maintaining
terminal state. This is covered in more detail in this
blog post.
libghostty-vt is already available and usable today for Zig and C and
is compatible for macOS, Linux, Windows, and WebAssembly. The functionality
is extremely stable (since its been proven in Ghostty GUI for a long time),
but the API signatures are still in flux.
libghostty is already heavily in use. See examples
for small examples of using libghostty in C and Zig or the
Ghostling project for a
complete example. See awesome-libghostty
for a list of projects and resources related to libghostty.
We haven't tagged libghostty with a version yet and we're still working on a better docs experience, but our Doxygen website is a good resource for the C API.
Ghostty-only Terminal Control Sequences
We want and believe that terminal applications can and should be able to do so much more. We've worked hard to support a wide variety of modern sequences created by other terminal emulators towards this end, but we also want to fill the gaps by creating our own sequences.
We've been hesitant to do this up until now because we don't want to create more fragmentation in the terminal ecosystem by creating sequences that only work in Ghostty. But, we do want to balance that with the desire to push the terminal forward with stagnant standards and the slow pace of change in the terminal ecosystem.
We haven't done any of this yet.
Crash Reports
Ghostty has a built-in crash reporter that will generate and save crash
reports to disk. The crash reports are saved to the $XDG_STATE_HOME/ghostty/crash
directory. If $XDG_STATE_HOME is not set, the default is ~/.local/state.
Crash reports are not automatically sent anywhere off your machine.
Crash reports are only generated the next time Ghostty is started after a crash. If Ghostty crashes and you want to generate a crash report, you must restart Ghostty at least once. You should see a message in the log that a crash report was generated.
Note
Use the
ghostty +crash-reportCLI command to get a list of available crash reports. A future version of Ghostty will make the contents of the crash reports more easily viewable through the CLI and GUI.
Crash reports end in the .ghosttycrash extension. The crash reports are in
Sentry envelope format. You can
upload these to your own Sentry account to view their contents, but the format
is also publicly documented so any other available tools can also be used.
The ghostty +crash-report CLI command can be used to list any crash reports.
A future version of Ghostty will show you the contents of the crash report
directly in the terminal.
To send the crash report to the Ghostty project, you can use the following CLI command using the Sentry CLI:
SENTRY_DSN=https://e914ee84fd895c4fe324afa3e53dac76@o4507352570920960.ingest.us.sentry.io/4507850923638784 sentry-cli send-envelope --raw <path to ghostty crash>
Warning
The crash report can contain sensitive information. The report doesn't purposely contain sensitive information, but it does contain the full stack memory of each thread at the time of the crash. This information is used to rebuild the stack trace but can also contain sensitive data depending on when the crash occurred.