fa1.dev · Dart & Flutter

One agent harness.
Every device.

Fa is a coding agent with a real tool loop — a sandboxed shell, git, interpreters, and a file browser — built on a pure-Dart core that runs on iOS, Android, web, desktop, and in your terminal. Same harness, same tools, everywhere. This page is the proof: the app below runs entirely in your browser.

▶ Try it in your browser GitHub pub.dev

iOS
Android
Web
macOS
Windows
Linux
CLI

Live demo

Try it right here.

The full agent app as static files — no server, no account. Pick a provider, paste your own key, and put the agent to work. Its sandbox shell (curl, jq, rg, git, python3, sqlite3) runs in an in-memory filesystem on your machine.

Bring your own key: it is held in memory only — never persisted, gone on reload. OpenRouter works from browsers; some providers block cross-origin calls (see BYOK).

Install

Get the CLI.

Fa runs in your terminal on macOS, Windows, and Linux. The installer is non-interactive: it checks for the Dart SDK, activates the package from pub.dev, adds the pub cache to your PATH, and exits. Run the separate setup wizard afterward to configure your provider, model, and API key.

Install method

macOS / Linux / WSL — install

curl -fsSL "https://fa1.dev/install.sh?v=2" | sh

Fa mobile app

The full iOS / Android / desktop sandbox, from source.

git clone https://github.com/IstiN/flutter_agent_harness
cd flutter_agent_harness/flutter_app
flutter run

Web demo

No install at all — the full agent runs in your browser with your own key. Try it above ↑ or open it full screen ↗.

Capabilities

A real workbench, not a chat box.

A real shell in a sandbox

curl · wget · jq · yq · rg · sed · awk · find · xargs · diff · patch · tar · zip, plus nslookup/dig/whois. On web it is a pure-Dart memory shell; on mobile the same commands run as WASM (uutils coreutils + ripgrep).

git over HTTP/SSH

Pure-Dart git: smart-HTTP clone and push, SSH remotes, commits and diffs. No native binary — it works the same in a browser tab as on a phone.

python3 · qjs · sqlite3

Interpreters stream in from a CDN on demand: Python 3 (with pip installs into the sandbox), QuickJS, and SQLite via sql.js. The agent picks the right tool for the job.

Secrets redaction

Secret values never reach the model, the transcript, or session files. The agent references them as $NAME in shell commands; redaction hooks scrub tool output on the way back.

File browser

A live view of the exact filesystem the agent works in — browse, preview, and watch files appear as the agent writes them. No hidden state.

Sessions + compaction

Append-only JSONL session trees you can resume and fork, with automatic LLM-powered compaction when the context window fills up.

Runs everywhere

One core, every form factor.

The harness is pure Dart — no dart:io in the core — so the same agent loop, tools, and session format run behind any ExecutionEnv: browser memory FS, phone sandbox, or your host shell.

Capability	Browser	macOS	iOS	Android	Windows
Agent loop, tools, sessions, compaction	✓	✓	✓	✓	✓
Chat UI + file browser	✓	✓	✓	✓	✓⁴
Shell: curl, jq, rg, sed, awk, tar, zip, diff, patch…	pure-Dart builtins	host shell	WASI binaries	WASI binaries	host shell
python3 + pip (pure-python wheels)	pyodide CDN¹	host	CPython 3.14 WASI	CPython 3.14 WASI	host
sqlite3	sql.js CDN¹	host	WASI	WASI	host
JavaScript (qjs) / lua	qjs CDN¹ · lua —	host	qjs + lua WASI	qjs + lua WASI	host
git — local ops	✓ dart_git	✓	✓	✓	✓
git — clone / push (remote)	— CORS²	✓	✓ HTTP+SSH	✓ HTTP+SSH	✓
ssh / scp / sftp · dig / whois	~ DoH+RDAP³	✓ host	✓ builtins	✓ builtins	~ ssh⁵
File upload + persistence	IndexedDB (upload UI)	host FS	app sandbox	app sandbox	host FS
Secrets — env injection + redaction	✓ in-memory	✓ .env	✓	✓	✓ .env

✓ full support · ~ partial / host-dependent · — not possible on the platform.
¹ Web interpreters (pyodide, quickjs-emscripten, sql.js) lazy-load from jsDelivr on first use. ² Browsers can't reach remote git (CORS) — local repos work fully. ³ No raw TCP in browsers: DNS-over-HTTPS and RDAP whois work; ssh/scp/sftp report unavailable. ⁴ Windows and Linux share the tested desktop code path; manual testing happens on macOS + iOS simulator. ⁵ Windows has no stock dig/whois; ssh/scp/sftp work via the built-in dartssh2 client on platforms with the Dart builtins, or the host OpenSSH client on desktop.

BYOK

Your key never leaves your browser.

Straight to the provider

API calls go directly from your machine to the provider. This page is static files — there is no server, no proxy, and nothing in the middle to log your key.

In-memory only

The key lives in page memory: never persisted, never written to localStorage, cookies, or disk — and gone on reload. The app's web secrets store is in-memory by design.

CORS is the only catch

The provider must allow cross-origin browser requests. OpenRouter does. api.anthropic.com and Ollama Cloud do not — reach those models through OpenRouter instead. Self-hosted endpoints need CORS headers.

FAQ

Straight answers.

What is Fa?

Fa (Flutter Agent Harness) is an open-source coding agent for Dart and Flutter. It pairs a pure-Dart agent core (provider adapters, tool loop, session tree, compaction) with a real sandboxed workbench: shell commands, git, python3 and sqlite3 — running identically on iOS, Android, web, desktop, and as a CLI.

Is my API key safe in the web demo?

Yes. The key is held in page memory only — never written to localStorage, cookies, or disk, and gone on reload. API calls go directly from your browser to the LLM provider: this page is static files, so there is no server or proxy in between that could log it.

Which LLM providers does Fa support?

OpenAI-compatible endpoints (OpenRouter, Ollama Cloud, self-hosted llama.cpp / LM Studio / vLLM), Anthropic, and Google. Custom OpenAI-compatible providers can be added with a base URL — the model list, context window, and output limits are detected from the endpoint automatically.

Which platforms does Fa run on?

iOS, Android, web (as static files, no server), macOS, Windows, Linux, and a terminal CLI. The core library is pure Dart with no dart:io, so the same agent loop and tools run everywhere behind a small environment abstraction.

What can the agent actually do?

Run shell commands (curl, jq, rg, sed, awk, tar, zip, diff, patch), clone and push git repositories over HTTP/SSH, run python3 with pip, query sqlite3, execute QuickJS, edit files, browse the web, and keep long-running sessions with automatic context compaction. All of it inside a sandbox you can inspect live in the file browser.

Is Fa free?

Fa itself is free and open source (MIT license). You bring your own provider key and pay your LLM provider only for the tokens you use — there is no markup, subscription, or account.

How do I install the CLI?

One line: curl -fsSL "https://fa1.dev/install.sh" | sh (macOS / Linux / WSL) or the PowerShell equivalent on Windows, then run the setup wizard to pick a provider and key. Alternatively dart pub global activate flutter_agent_harness from pub.dev. Both give you the fa and fah commands.

One agent harness.Every device.