cinder

Cinder

A mobile Claude Code client. Run the real Claude Code CLI on an Android phone — not a reimplementation, not a remote shell, not a web wrapper. Anthropic's official claude binary executes inside a self-contained Linux sandbox that ships with the app, and a Jetpack Compose UI renders its output as a proper transcript.

Unofficial and unaffiliated with Anthropic. Sideload only. arm64-v8a.

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What it is (and what it isn't)

Cinder is a front-end. It does not contain, copy, or reimplement Claude Code. The claude binary is Anthropic's, published on the public npm registry, and the app downloads it at runtime from Anthropic's own servers — exactly as it would install on a laptop. You then sign in with your own Anthropic account through the CLI's own login. Cinder is the thing that presses "download," provides a Linux environment for the binary to run in, and draws the UI.

The analogy is a universal remote: it doesn't contain the TV, it talks to one you already own. What is bundled in the APK is open-source infrastructure (proot, an Alpine rootfs, small Termux libraries), each credited with its license below.

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Features

• Runs the real Claude Code CLI on the phone, in a bundled Linux sandbox
• Chat transcript in Claude Code's style — tool cards, Edit diffs, collapsible results
• Code canvas — fenced code blocks render as scrollable panels with a copy button
• Live file status per operation — a row says what it actually did: creating file · 84 lines written → file created · 212 lines, or file edited · +12 −3 lines, appended, file deleted
• Live turn marker — never blank while a turn is in flight: working…, then thinking… ~N tokens with a ticking clock and the effort level, then responding… ~N tokens as output streams
• Per-agent stop — spawned agents show a spinner while they run and a tick when they finish, each with its own stop wired to the CLI's stop_task
• Markdown and LaTeX rendering — headings, lists, tables, quotes, links and inline code, with maths in $…$ / $$…$$ / \(…\) form drawn as styled text (no WebView, no KaTeX)
• Permission prompts on the phone — in any mode that asks, the tool call parks with its actual command or path shown and an allow/deny card above the composer; all six CLI permission modes (plan, manual, acceptEdits, auto, dontAsk, bypassPermissions) are selectable
• Real context-window readout — the window is read from the CLI rather than assumed, and is tracked per conversation
• Subagent panel — a collapsible list of spawned agents with their names and output so far
• Ultracode toggle — the keyword is highlighted as you type it, with a one-tap skip for a single turn
• Voice input — dictate a prompt, optionally sent the moment the recognizer finishes
• Find in conversation and a searchable settings screen
• Survives being backgrounded — a foreground service and wake lock hold the process while a turn is in flight, since the CLI is a child of it
• CLI updater — checks the installed version and updates in place
• Back peels off one layer at a time — preview, then drawer, then find, then back to chat; at the root it backgrounds the app rather than finishing it, because the CLI is a child of this process and finishing would end a running turn
• Wake-up markers — a turn started by a background monitor, a finished task or a scheduled fire says so (woken by a background task · completed · …) instead of reading as a new session
• Sign in with an Anthropic account via /login in chat — the CLI's own OAuth over a real PTY
• Session history in a side drawer — resumes with --resume, reloading real context
• Live model picker — queries /v1/models with the stored OAuth credential
• Built-in terminal, file upload, tap-to-download for files the agent creates
• One-tap workspace cleanup — empties /workspace without touching the CLI, the musl rootfs, or any installed toolchain, so nothing has to be reinstalled
• Package management without root — apk add, npm -g, pip install, plus APK build/decompile tools

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The engineering: five problems worth writing down

Most of the work here was not UI. It was making a 250 MB Linux binary run on Android at all. Each of these first presented as something unrelated.

1. The CLI is dynamically linked against musl

Claude Code ships one prebuilt native binary per platform — no source to cross-compile, no Android target. The linux-arm64-musl build is the closest fit, but its ELF headers show it is dynamic: its interpreter is /lib/ld-musl-aarch64.so.1, a loader at an absolute path Android doesn't have and won't let you create without root. Hence proot with an Alpine rootfs — and because it's musl, that rootfs is 4 MB, not a 400 MB Debian.

2. targetSdk = 28, deliberately

Apps targeting API 29+ cannot execute binaries from their own writable data directory, which the sandbox depends on. Termux solved it the same way. This is why Cinder is sideload-only — the Play Store requires a current target API.

3. aapt silently renames .gz assets

The rootfs shipped as assets/rootfs.tar.gz, but the build tool gunzips and renames such assets, so it arrived as assets/rootfs.tar — and opening rootfs.tar.gz threw FileNotFoundException. Bootstrap failed on every launch while everything looked fine. Renaming to rootfs.tgz plus noCompress fixed it.

4. Login needs a real terminal

claude auth login puts the terminal in raw mode and reads keystrokes directly; given a pipe it never reads stdin, so a pasted code went nowhere — silently. The fix is a small JNI library (libptyexec.so, about 90 lines of C) calling forkpty. The code must end with a carriage return, not a newline.

5. Android has no SysV IPC — so apk needed a workaround

Alpine's minirootfs ships no /etc/resolv.conf, so every request died with a DNS timeout until nameservers were written in from ConnectivityManager. Then apk failed its database write: apk-tools v3 locks the DB with a SysV semaphore, and Android kernels are built without CONFIG_SYSVIPC. The workaround: run apk under a nested proot -0 (userspace fake root), which extracts the full dependency tree correctly — the only failure is the final DB bookkeeping, which happens after every file is on disk, so it's cosmetic and filtered from output.

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Installing packages inside the sandbox

Nothing runs as device root. proot's -0 is userspace fake root — no Magisk, no unlocked bootloader, no kernel involvement.

On the SDK/NDK: Google ships the Android SDK build-tools and NDK as x86-64 Linux binaries; they cannot execute on an ARM phone. Cinder installs the Termux aarch64 builds of aapt2, d8, apksigner and ecj, plus Google's architecture-independent android.jar and Gradle — a genuine ecj to d8 to aapt2 to apksigner pipeline. apktool and jadx run on Alpine's musl JVM.

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Building

git clone https://huggingface.co/SmallAICreator/cinder
cd cinder
./gradlew assembleDebug
adb install -r app/build/outputs/apk/debug/app-debug.apk

Requires the Android SDK with NDK 27 (for the PTY library) and JDK 17. arm64-v8a only.

First run: open setup (bundled runtime installs itself), then download claude (~250 MB from npm, wifi recommended), then in chat type /login, then optionally install the build or decompile toolchains.

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Licensing and attribution

Cinder bundles these open-source components. Sources are at the links, as their licenses require:

Claude Code itself is not included. It is Anthropic's software under its own terms (https://code.claude.com/docs/en/legal-and-compliance) and is downloaded at runtime by the user, from Anthropic's official distribution. Claude and Claude Code are trademarks of Anthropic PBC; this project is unofficial and not endorsed by or affiliated with Anthropic.

Application code in this repository is MIT licensed.