Why I Built an Open-Source, E2EE‑Synced Termius Alternative (and What Broke Along the Way)

Description and use

Shellit is a cross‑platform SSH client with zero‑knowledge self‑hosted sync and production safety guard, built on Dart/Flutter.

Problem

Developers relied on paid, closed‑source SSH clients that lock key management and server metadata in proprietary clouds, limiting cross‑platform performance and security.

Outcome

Shellit delivers a lightweight, cross‑platform SSH client with zero‑knowledge encrypted sync, production safety guardrails, and native AI integration, addressing the limitations of paid and heavy open‑source alternatives.

Workflow

• 1. Define core requirements: cross‑platform, lightweight, zero‑knowledge sync, safety guard, AI integration.
• 2. Choose Dart & Flutter for native UI and performance.
• 3. Implement production guard: tag environments, add red border, parse destructive commands, show confirmation modal.
• 4. Build self‑hosted sync relay: lightweight Docker image, encrypt data with Argon2id & AES‑256‑GCM, use HTTP over Tailscale/WireGuard.
• 5. Create MCP server for AI assistants to run commands safely.
• 6. Add matrix tiling and broadcast input for multi‑terminal workspaces.
• 7. Enforce contract‑first monorepo structure with core foundation, storage vault, SSH core, terminal UI, plugin SDK, and sync server.
• 8. Resolve platform bugs: Windows IME focus, tab destruction, Argon2id re‑keying, Android key sync.
• 9. Test extensively: 200+ unit/widget tests, 24 documented bug post‑mortems.
• 10. Release under GPLv3 and open source on GitHub.

Evidence

Shellit is a cross‑platform SSH/SFTP client, server management hub, and terminal workspace built from scratch using Dart & Flutter.

Source

All server entries, SSH keys, snippets, and directory mappings are derived and encrypted on-device via Argon2id and AES-256-GCM.

Source

The terminal pane receives a distinctive pulsing red warning border.

Source