Fa fa1.dev

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, in your terminal, in Chrome, and in Outlook. Same harness, same tools, everywhere. This page is the proof: the app below runs entirely in your browser.

▶ Try it in your browser Join the public beta on TestFlight Download for macOS (no sandbox) Chrome extension Outlook add-in GitHub pub.dev
  • iOS
  • Android
  • Web
  • macOS
  • Windows
  • Linux
  • CLI
  • Chrome
  • Outlook

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 detects your OS and architecture, downloads a prebuilt binary from the latest GitHub Release, puts it on your PATH, and exits. On macOS it also strips Gatekeeper quarantine and re-signs the binary ad-hoc so it runs without a manual security override. Run the separate setup wizard afterward to configure your provider, model, and API key.

macOS / Linux / WSL — install 
curl -fsSL "https://fa1.dev/install.sh" | 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

Chrome extension

Fa lives in your browser: it reads the page, drives tabs, takes screenshots and answers with the full tool loop. Download the zip, unzip it, then open chrome://extensions, enable Developer mode, Load unpacked → pick the unzipped folder and pin Fa from the puzzle-piece menu.

Outlook add-in

Fa lives in your mailbox: a taskpane chat that reads the open email, reads its attachments, and writes draft bodies — every mail tool approval-gated. Sideload it once: download manifest.xml, open aka.ms/olksideload (My add-ins), then Custom add-ins → “+ Add a custom add-in” → Add from file. Microsoft removed the manual “Add from a URL” entry — download-then-file is the only self-service path. Full guide: Outlook install guide.

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.

The full tool belt

Every platform ships the same core tools: read · write · edit · ls · bash · web_search · web_fetch · task subagents · lsp · memory_search · checkpoint/rewind · ask · request_secret — plus the mcp__ servers you configure. Hosts add their own: 34 browser tools in the Chrome extension, three mail tools in Outlook. Full list in llms.txt.

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 BrowsermacOSiOSAndroidWindows
Agent loop, tools, sessions, compaction ✓✓✓✓✓
Chat UI + file browser ✓✓✓✓✓⁴
Shell: curl, jq, rg, sed, awk, tar, zip, diff, patch… pure-Dart builtinshost shellWASI binariesWASI binarieshost shell
python3 + pip (pure-python wheels) pyodide CDN¹hostCPython 3.14 WASICPython 3.14 WASIhost
sqlite3 sql.js CDN¹hostWASIWASIhost
JavaScript (qjs) / lua qjs CDN¹ · lua —hostqjs + lua WASIqjs + lua WASIhost
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 FSapp sandboxapp sandboxhost 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.

Add-ons

The same agent, in your browser and your inbox.

Two hosts ship straight off this site, built from the same pure-Dart core. Both are static artifacts — no server, no account.

Chrome extension (MV3)

The side panel hosts the full Fa app; the agent runs in the service worker and gains 34 browser tools — tabs_*, windows_*, bookmarks_*, downloads_*, cookies_*, history_search, inject_js, cdp_eval, page_screenshot, and more. Reach it from the side panel, the omnibox (fa <query>), the Ctrl+Shift+1 hotkey, or the context menu on any selection. Every page-derived byte is quarantined as untrusted data; code injection prompts on every call by default — only an explicit yolo session drops that guard.

Download fa-extension.zip — install steps in Install ↑.

Outlook add-in

The same agent as an Office taskpane (Mailbox 1.8+). Three mail tools: outlook.read_current_item (metadata + body of the open email), outlook.read_attachment, and outlook.insert_draft_body — the latter two always prompt. Email bodies enter the context only inside a quarantine fence marked untrusted, so instructions in a message can never drive the agent. Ask about the open email, get attachments summarized, or dictate a reply straight into the compose pane.

Sideload: download manifest.xml, open aka.ms/olksideload → My add-ins → Custom add-ins → “+ Add a custom add-in” → Add from file (Microsoft removed the manual “Add from a URL” entry). In new Outlook (Windows) and OWA the «fa» button lives in a message's Apps flyout; classic Outlook shows it on the Home ribbon. Full guide: install + troubleshooting.

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 — plus a Chrome MV3 extension that hosts the full agent in your browser and an Outlook add-in that runs it inside your mailbox. 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, spawn task subagents, use LSP and MCP servers, keep persistent memory, and — through the Chrome extension — drive tabs, history, bookmarks, downloads, cookies, and screenshots with approval-gated injection. Inside Outlook it reads the open email and its attachments and writes draft bodies.

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. The installer downloads a prebuilt binary from GitHub Releases and, on macOS, removes Gatekeeper quarantine and re-signs it ad-hoc. Then run the setup wizard to pick a provider and key. You can also install via dart pub global activate flutter_agent_harness from pub.dev if you already have the Dart SDK.

How do I install the Chrome extension?

Download fa-extension.zip, unzip it, open chrome://extensions, enable Developer mode, Load unpacked → pick the unzipped folder, and pin Fa from the puzzle-piece menu. The side panel hosts the full Fa app; the agent gains 34 browser tools — tabs, windows, history, bookmarks, downloads, cookies, screenshots, and approval-gated code injection.

Does Fa run inside Outlook?

Yes — as an Office Add-in. Download fa1.dev/outlook/manifest.xml, open aka.ms/olksideload (My add-ins), then Custom add-ins → “+ Add a custom add-in” → Add from file → manifest.xml → Install — Microsoft removed the manual “Add from a URL” entry, so download-then-file is the only self-service path. Works in Outlook on the web, new Outlook for Windows, and classic Outlook. The taskpane runs the full agent with three approval-gated mail tools: read the open email, read attachments, and insert draft bodies. Full guide: Outlook install guide.