Grass vs Happy Coder: Two Mobile Clients for Claude Code Compared

Grass and Happy Coder both let you monitor and control Claude Code from your phone — during sessions that, at the 99.9th percentile, now exceed 45 minutes per turn according to Anthropic's research on agent autonomy. Grass connects directly from your phone to your machine over local WiFi or Tailscale — no relay, no third-party server, no external dependency. Happy Coder routes session data through an encrypted relay server, which removes the need for Tailscale but means data leaves your local network. If you want a fully local connection, OpenCode support, or a native iOS app, Grass is the stronger fit. If you specifically need Codex support or want an open-source encrypted relay, Happy Coder is worth a look.

TL;DR

• Both support Claude Code from mobile with QR-code pairing and permission approval
• Happy Coder routes data through an encrypted relay server; Grass is local-only by default (no relay)
• Grass supports Claude Code and OpenCode; Happy Coder supports Claude Code and Codex
• Happy Coder is open source and cross-platform; Grass has a native iOS app with an Android PWA
• Both support voice input; Happy Coder has a dedicated voice agent (subscription for extended use); Grass uses the phone's native voice keyboard

What is Happy Coder?

Happy Coder is an open-source mobile and web client for Claude Code and Codex, built by a team of engineers who wanted to monitor their AI coding sessions away from their desks. It works by replacing the claude or codex command with happy — the CLI wraps your agent session, encrypts the data, and syncs it to your phone via Happy's relay server. The encryption uses the same approach as Signal (TweetNaCl), and the zero-knowledge architecture means Happy's servers never see your data in plaintext. The Happy Coder GitHub repository and documentation are publicly available.

What is Grass?

Grass is a native iOS app (with an Android PWA) for monitoring and controlling coding agents running on your own machine or a transient dev server like Daytona. You run grass start in your project directory and scan the QR code — no relay server is involved. Agent output streams directly from your machine to your phone over HTTP and SSE, either over local WiFi or via Tailscale for remote access. Grass supports Claude Code and OpenCode. It is free for local use.

Head-to-head: Happy Coder vs Grass

The most significant architectural difference is the connection model. Happy Coder's relay approach means your session data can reach your phone regardless of network topology — you do not need your phone and machine on the same network, and you do not need to configure Tailscale. The trade-off is that data leaves your local network, even if it is encrypted in transit. Grass's direct connection approach means no data leaves your network at all; the agent output goes from your machine to your phone and nowhere else. For remote access, Grass requires Tailscale or a public IP.

The agent support difference is also meaningful. Happy Coder wraps Claude Code and Codex (OpenAI's coding agent). Grass supports Claude Code and OpenCode. If your workflow involves Codex, Happy Coder is the only option of the two. If you use OpenCode, Grass is the only option.

When to use Happy Coder

Happy Coder is the right choice when encrypted relay access is a priority — particularly if you work with sensitive codebases and want an open-source, auditable solution with formal end-to-end encryption guarantees. It is also the better fit if you primarily use Codex rather than Claude Code, or if you want voice coding as part of your mobile workflow. The open-source nature of Happy Coder gives security-focused developers full visibility into the relay architecture and encryption implementation, which is a meaningful advantage for those who want to audit the code themselves.

When to use Grass

Grass is the right choice when you want a fully local connection with no relay involved, or when you use OpenCode alongside Claude Code:

No relay, no external dependency. Grass connects directly from your phone to your machine over local WiFi or Tailscale. There is no cloud relay to depend on, no third-party server in the path, and no account required on the server side. The connection works identically whether or not Happy Coder's infrastructure is operational.

OpenCode support. If your workflow includes OpenCode, Grass supports it natively. Happy Coder does not.

Native iOS app. Grass is purpose-built for iOS — it is not a port of a web or desktop app. The native implementation means tighter system integration, and the app is distributed through the App Store rather than requiring a PWA install or web browser.

Daytona and remote server integration. Grass has built-in support for connecting to remote coding sessions on Daytona workspaces using grass start --network tailscale or grass start --network remote-ip. This makes it straightforward to run mobile coding agent access for agents running entirely in the cloud.

The bottom line

Grass and Happy Coder are genuine alternatives for the same core use case, unlike most of the other comparisons in this space. The choice comes down to architecture preference and agent support. If you want an open-source, encrypted relay with Codex support and a cross-platform app, Happy Coder is a solid choice. If you want a fully local connection, OpenCode support, a native iOS app, or tight Daytona integration, Grass fits better. For most developers, the right answer depends less on features and more on which architectural model matches their security posture and which agents they actually run.

Frequently asked questions

Does Happy Coder support OpenCode as well as Claude Code?

Happy Coder supports Claude Code and Codex (OpenAI's coding agent). It does not support OpenCode. Grass supports Claude Code and OpenCode — you choose per-session in the agent picker. If your workflow uses OpenCode, Grass is the only mobile client of the two that covers it.

Is Happy Coder open source?

Yes. Happy Coder is available on GitHub under an open source license. Grass's CLI (@grass-ai/ide) is also open source. The Grass native iOS app is closed source.

How do Grass and Happy Coder each handle agent approval gates?

Both surface Claude Code approval gates on mobile. Grass uses a global permission manager that queues gates from all connected servers and shows them as native modals regardless of which screen you're in — including when the app is in the background. Happy Coder also handles permission requests in its mobile interface. The key structural difference is that Grass aggregates gates across multiple concurrent servers, which matters if you're running more than one agent session simultaneously.

Which is easier to set up — Grass or Happy Coder?

Both follow a similar setup pattern: install a CLI on the machine running Claude Code, scan a QR code from the mobile app, and connect. Grass CLI is installed via npm install -g @grass-ai/ide and started with grass start. Happy Coder replaces your claude command with happy. Both tools are designed for a fast first-connection experience. Neither requires an account to get started.

Can I use Grass or Happy Coder with a remote server, not just my local laptop?

Grass explicitly supports remote connections: grass start --network tailscale or grass start --network remote-ip generates a QR code with the correct external address for Tailscale or public IP access respectively. Grass also has first-class Daytona integration for cloud-based transient dev server setups. Check Happy Coder's documentation for its current remote access support.

Which tool should I use if I'm just getting started with Claude Code on mobile?

Either is a reasonable starting point. Grass is the right choice if you want to run OpenCode alongside Claude Code, need to manage multiple concurrent sessions, plan to use Daytona for remote agent runs, or want a native iOS app rather than a cross-platform client. If you're exclusively on Claude Code and want to explore an open-source option with encrypted relay access, Happy Coder is worth trying. Both are free to use locally.