# Mozc: The Open-Source Release of Google Japanese Input for Linux, macOS, Windows, and Android

> Mozc is the open-source version of Google Japanese Input, a multi-platform Japanese input method editor (IME) that covers Android, macOS, Chromium OS, GNU/Linux, and Windows. It originates from the same codebase as the proprietary Google Japanese Input product, released without Google's official QA process or user support, and has no stable release concept.

**google/mozc** — Mozc - a Japanese Input Method Editor designed for multi-platform

- Repository: https://github.com/google/mozc
- Stars: 2,992 · Forks: 544
- Language: C++
- License: NOASSERTION
- Published: 2026-09-24 · Updated: 2026-09-24 · Language: en
- Canonical page: https://hysenlabs.com/projects/google-mozc

## The Open-Source Subset of Google Japanese Input

Google Japanese Input is a proprietary Japanese IME developed inside Google under the internal codename Mozc. The open-source project released to GitHub shares the same origin but is not the same product. The README is specific about this: Mozc is a subset of Google Japanese Input, released as source code under an open-source license, without any warranty or user support from Google. Google Japanese Input, the app available for Android and other platforms, includes features and data not present in the Mozc OSS release.

The README links to an About Branding document at `docs/about_branding.md` for a detailed list of differences between the two. The name Mozc itself has two meanings inside Google: the internal code name for Google Japanese Input generally, and the specific OSS project on GitHub. In the context of this repository, Mozc means the second.

## Platform Coverage and Build Status

Mozc supports Android (as a library, `libmozc.so`), macOS, GNU/Linux, and Windows. Chromium OS is also listed. The CI build status table in the README shows separate GitHub Actions workflows for Linux, Windows, macOS, and the Android library build. This means the codebase is tested continuously across all four platform categories.

The build instructions are split by platform: `docs/build_mozc_for_android.md` for the Android library, `docs/build_mozc_for_linux.md` for Linux desktop, `docs/build_mozc_in_osx.md` for macOS, and `docs/build_mozc_in_windows.md` for Windows. Each document covers the specific toolchain and dependencies for that platform. The source code is in C++ with the `src/` directory as the root. Docker configuration in the `docker/` directory provides containerized build environments for some platforms.

## Building Mozc from Source

Mozc does not provide pre-built binary packages through the repository. Installation requires building from source using the platform-specific documentation. On Linux, the typical path involves the build instructions in `docs/build_mozc_for_linux.md` and a tool like Bazel, though the exact toolchain requirements are specified in the build docs rather than the README.

For Linux desktop environments, Mozc is available through distribution package managers in many cases; for example, `fcitx-mozc` packages Mozc as a backend for the fcitx input framework. The README mentions fcitx-mozc in the context of related search terms but does not document the packaged installation path directly. Users who want to avoid building from source on Linux should check whether their distribution's package repository carries a Mozc package. The README explicitly states the repository is not an officially supported Google product, so packaged versions from distribution maintainers are independent efforts.

## The No-Stable-Release Policy

Mozc does not follow a stable release model. The README states this directly: "There is no stable version." The rationale is that Google does not promise official QA for the OSS project, so a concept of stability tied to a release tag would be misleading. Instead, the project increments the version number with each non-trivial change.

The practical consequence for packagers and distributors is that any version is considered as stable as any other in the absence of formal QA. The README explicitly invites packagers to pick any version. The Release History page at `docs/release_history.md` provides information about recent changes that would be relevant for version selection. This policy removes the usual expectation that tagged releases are more trustworthy than arbitrary commits, which is an unusual design choice and a genuine caveat for teams that rely on version pinning for reproducibility.

## Vocabulary Policy and Dictionary Coverage

Mozc's conversion quality depends on its dictionary data. The README links to a `VOCABULARY_POLICY.md` file that describes the policies governing what vocabulary and conversion results the IME includes and excludes. This is relevant for users who encounter unexpected conversion results or who need to understand why certain terms are not suggested.

The `src/data/dictionary_oss/` directory holds the open-source dictionary data, with its own README noting that the dictionary has mixed licensing from multiple sources. The test dictionary at `src/data/test/dictionary/` carries the same licensing terms. Third-party code under `src/third_party/` is governed by its own per-directory copyright notices. Teams integrating Mozc into a product should review the dictionary licensing section to understand the full licensing picture, not just the top-level BSD 3-Clause terms on the Google-written code.

## Alternatives, Maintenance, and License

ibus-anthy is a widely available alternative Japanese IME for Linux that uses the Anthy conversion engine. The key difference from Mozc is the underlying conversion technology: Mozc derives from Google Japanese Input's conversion model, while Anthy is a standalone open-source engine that has not been updated from a Google training base. For users who care about conversion quality on modern Japanese text including internet vocabulary and kanji, the difference between the two engines can be material.

The last push to the Mozc repository was on 2026-09-25. The repository is not archived. The project is maintained by Google and is listed as copyright 2010-2026 Google LLC in the README, though it is explicitly not an officially supported Google product. The BSD 3-Clause license on Google-written code requires only attribution; third-party components in `src/third_party/` carry their own licenses and should be checked before distribution.

## Conclusion

Mozc is the right choice for Linux, macOS, Android, and Chromium OS users who want a Japanese IME with the same dictionary and conversion technology as Google Japanese Input, and who can accept building from source. Packagers should note that there is no stable release version; any version can be used, and they are described as equally stable in the absence of official QA. The BSD 3-Clause license is permissive and imposes only attribution requirements. The last push to the repository was on 2026-09-25. Verify the build documentation for your specific platform in the docs/ directory before starting.

## FAQ

### What is Mozc?

Mozc is the open-source version of Google Japanese Input, a Japanese IME designed for multiple platforms including Android, macOS, Chromium OS, GNU/Linux, and Windows. It is developed by Google but is not an officially supported Google product and ships without warranty or user support.

### How to enable Japanese input using Mozc?

The README does not provide a step-by-step configuration guide. It points to platform-specific build documentation in the docs/ directory for Linux, macOS, Windows, and Android. On Linux, distribution packages like fcitx-mozc are available in many package managers as an alternative to building from source.

### What is the Google Japanese input app?

Google Japanese Input is the proprietary IME product from which Mozc originates. According to the README, Mozc is a subset of Google Japanese Input released as open-source code. The About Branding document at docs/about_branding.md describes the detailed differences between the two.

## Sources

- [google/mozc on GitHub](https://github.com/google/mozc)
- [Issues](https://github.com/google/mozc/issues)
- [README](https://github.com/google/mozc/blob/master/README.md)

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Hysen Labs editorial analysis, written from the project's own repository and release notes. Cite the canonical page: https://hysenlabs.com/projects/google-mozc