Open-source alternative to sites/artifacts

Flats

Ask your AI agent for a web page, a shared document, a small app, a design or a whiteboard. Flats hosts it on your own machine and gives you a link.

Quick start · What you can make · How Flats compares · Documentation

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Each thing Flats hosts is a flat: one web page, document, app, design or board with its own name and link. Your agent creates and updates flats. You decide in the Flats console what goes live and who can open it.

1. Ask your agent: "Make a one-page report of our Q3 numbers with a chart and put it on Flats."
2. Approve it in the Flats console. The agent sends you the approval link.
3. Open the link. The page starts Private, on your machine. Share it on a private network such as Tailscale, or make it Public when you are ready.

What you can make

You want	Flats makes a	How it changes
A report or dashboard with charts you can send around	Page: one HTML document with its assets	You approve saving and publishing each version
Notes, a handbook or meeting minutes that people and agents edit together	Document: live, collaborative Markdown	Edits apply at once and are kept as revisions
A small internal tool with a database, such as a poll, tracker or form	Website: a static site, or a small JavaScript server app with SQLite	You approve saving and publishing each version
Screen mock-ups and click-through prototypes	Design: a canvas of HTML artboards	Edits apply at once and are kept as revisions
A brainstorm, retro or flowchart that people rearrange by hand	Board: an infinite whiteboard with sticky notes, shapes and connectors	Edits apply at once and are kept as revisions

Every flat starts Private. Making any flat Public, or Private again, always waits for your approval. How changes go live has the details for each type, and content types has the full reference.

How Flats compares

	Flats	Hosted AI artifacts and sites (for example Claude Artifacts)	App hosting (for example Vercel, Netlify)
Where it runs	Your own Mac or Linux machine, or your own server	Usually the provider's cloud	Usually the provider's cloud
Where your data lives	Files and SQLite databases on that machine	Usually your account with the provider	Usually your account with the provider and the services you add
Which agents can use it	Any MCP client; a plugin for Claude Code, Codex and Cursor	Often the provider's own assistant	Usually any tool that can deploy there, such as a CLI or a Git push
Server code and a database	JavaScript server apps with SQLite and persistent files (details)	Varies by product	Often available through the provider's functions and add-ons
People and agents editing together	Documents, designs and boards, with history	Varies by product	Usually outside the hosting itself
Who decides what goes live	You approve every publish and visibility change in your console	Varies by product	Varies with your deployment setup

Other products change often; check their current documentation for details.

Quick start

1. Install Flats

On macOS or Linux, with an amd64 or arm64 machine:

curl -fsSL https://raw.githubusercontent.com/gosuda/flats/main/install.sh | sh

The installer verifies the release, installs flats to ~/.local/bin and starts it as a background service, without sudo. The console is at 127.0.0.1:7878. The default network is Local, so flats open only on this machine; other providers are off.

2. Connect your agent

Install the Flats plugin. In Claude Code:

claude plugin marketplace add gosuda/flats && claude plugin install flats@flats

In Codex:

codex plugin marketplace add gosuda/flats && codex plugin add flats@flats

Then restart or reconnect the agent. Connecting agents covers Cursor, other MCP clients and agents on another machine.

3. Ask for something

Try one of these:

• "Make a one-page report of last quarter's sales with a bar chart and put it on Flats."
• "Start a Flats document for our team handbook."
• "Build a lunch poll on Flats that saves votes."

4. Approve and open it

For a page or website, the agent saves a Private Draft and sends you a console link. Approve two requests there: saving the Draft as version 1, then publishing that version. Then open the link the agent gives you, such as http://coffee-report.localhost:7879. A document, design or board opens at once, without an approval.

Deploy without an agent, from the command line

mkdir -p hello
printf '<h1>Hello from Flats</h1>\n' > hello/index.html
flats save-draft hello ./hello

Run the exact flats create-version command printed by the save above; its --revision and --hash freeze the files you saved, even if someone edits the Draft afterwards. The command asks to save that Draft as version 1. Follow the approval URL it returns, or open the local console, and approve it. That creates v1 but puts nothing live yet. Deploy it with Publish v1 in the console, or request it from the CLI and approve that request too:

flats deploy --flat hello --version 1

Then visit hello.localhost:7879.

flats deploy returns exit code 3 while a request awaits approval, including with --json. Saving a Draft or a version does not make a site live; only deploying a version does.

Run flats status to check the host. See installation and upgrades for installer options, upgrades and backups.

Other ways to run Flats: container, foreground or source

Container

A Linux image for amd64 and arm64 is published with every release. On Linux, use host networking so the console, CLI and agents reach it on loopback:

docker run -d --name flats --restart unless-stopped --network host \
  -v flats-data:/data ghcr.io/gosuda/flats:latest

From a checkout, you can instead use Docker Compose (including Docker Desktop, on a host with trusted local containers):

docker compose up -d --wait

This keeps the console and local flats on host loopback and persists data in a named volume. See the Compose setup for image pinning, configuration and upgrades.

Never publish the console port to your network: anything that reaches it can approve deploys. See Running Flats in a container for other Docker hosts and network modes.

Foreground

flats serve --config ./flats-demo-data/config.json

On first start, this creates a host with the defaults in ./flats-demo-data. It never does that over a directory that already holds Flats data. Each running host needs its own data directory and ports; see Configuration and storage.

From source

Requires Go 1.27.1 or newer:

go install github.com/gosuda/flats/cmd/flats@latest

Use @main for unreleased changes. This build does not include NetBird; see Serving through NetBird to build the release binary from a checkout.

How changes go live

Websites and pages follow the version model: you work on a Private Draft while the live version keeps serving, and previews use isolated data. Saving a version (v1, v2, ...) and deploying it are separate approved steps, so a version can exist without ever going live. Publication and rollback require console approval.

Documents, designs and boards are edited live by people and agents together: private visitors can edit while public visitors read, unless you approve guest editing for a Public board, and changes to an already Public flat are visible immediately. Documents merge agent saves into people's edits; designs keep every change as a whole-canvas revision. Boards record each agent write as one revision and group each person's edits into revisions. Changing visibility in either direction requires approval for every type.

Explore content types for the full lifecycle and agent tools, including save_page, update_document and save_design. The Boards guide covers get_board, update_board, live collaboration, imports and history. Choose a board for ideas people will move and connect; choose a design for HTML screens and prototypes.

Agent integration

Connect Claude Code, Codex or Cursor with the Flats plugin, which runs flats mcp (the flats CLI must be on the agent's PATH) to relay the selected host's MCP endpoint; any other MCP client registers http://127.0.0.1:7878/mcp directly. The install commands are in the Quick start.

Without the plugin, register the MCP endpoint yourself. flats mcp-config prints the commands for Claude Code, Codex and Cursor with your host's address:

claude mcp add --transport http flats http://127.0.0.1:7878/mcp

Restart or reconnect the agent and list its tools to check the connection. In a terminal, flats status checks that the CLI reaches the host. flats connect chooses which host the CLI and the plugin talk to (loopback by default). It does not register an agent.

Connecting agents covers the other clients, remote hosts (flats connect), client updates and llms.txt. The agent starts with read-only check_client, then reads the server's current guide. For the whole server contract in one document, read resource flats://docs/runtime-api/v1 or call get_runtime_reference with {}. The runtime API v1 reference is embedded in the host and available through MCP without an installed skill or source checkout.

Static and server flats

Static builds need an index.html. For a JavaScript app, add a flats.json:

{"kind":"server"}

Then create server.js:

export default {
  async fetch(request, env) {
    env.DB.exec("CREATE TABLE IF NOT EXISTS hits (n INTEGER)");
    env.DB.exec("INSERT INTO hits VALUES (1)");
    const [{ n }] = env.DB.query("SELECT count(*) AS n FROM hits");
    return Response.json({ hits: n });
  }
};

Save the directory with flats save-draft <slug> <dir>, create a version with flats create-version <slug>, then deploy that version after approval. JavaScript runs in QuickJS on WebAssembly, with SQLite (env.DB), persistent string files (env.FILES), Web Crypto and WebSocket callbacks. There are no Node.js APIs; bundle imports into the uploaded version. Server-side fetch can call exact operator-granted HTTP(S) origins; see Calling external APIs.

WASI, persistent data and environment variables

A .wasm server is a WASI preview1 command instantiated afresh per request: request JSON on stdin, response JSON on stdout, only the flat's configured environment variables and secrets, with no inherited host environment, plus clocks and randomness. It has no SQLite/FILES host ABI, filesystem mounts, outbound network or WebSocket API. See the capability table and response format.

Data survives deploys and ordinary rollbacks. flats rollback hello restores code; --restore-data requests a separately approved restore of the pre-deploy DB and FILES snapshot. Preview data is isolated from live data.

Ordinary environment variables (flats env set hello GREETING 'Hello') and encrypted secrets reach server code as env.NAME, or as environment variables for WASI. Saving a value leaves running workers on their snapshot. The live worker picks up current values at the next approved deployment, redeployment, rollback or data restore, or when the Flats host restarts; a newly created preview also loads them. See App environment variables and Secrets.

Private and public access

Start locally, then enable the providers you need in Settings → Network providers. Allow a provider for an individual flat under Networks on its Settings tab.

Access	Providers
Private	Local (always on), Tailscale (tailnet ACLs), NetBird¹ (access policies), your reverse proxy (its own access control)
Public	Portal, Tailscale Funnel, zrok, Cloudflare quick tunnel, NetBird Expose¹, your reverse proxy

¹ NetBird and NetBird Expose are in the release binary (install.sh and the container image) but not in go install; see NetBird setup.

Host permission alone does not grant a provider to a flat. Configured provider defaults can grant providers to new flats; changing those defaults does not retroactively change existing flats. Tailscale permission does not imply Funnel permission.

Making a flat Public requires an approved transition and a configured, permitted public route. Websites and pages also need a published version; documents, designs and boards run without publication. Configuration alone never publishes or changes visibility. Wait for a route to report ready and verify its endpoint before sharing it: relay availability and network connectivity are external dependencies.

See Private and public access for provider setup, tailnet consoles, serving flats behind your own reverse proxy and upgrades from older hosts.

Security

• Sandboxed execution. Server code runs in separate worker processes with WebAssembly memory and time limits, bounded request bodies and WebSocket connections, SQLite and FILES quotas, and restricted host capabilities. Each flat and preview gets its own origin.
• Privileged console. The management listener and console can approve deployments. Approval decisions require the console header and a same-origin browser request. That is CSRF protection, not authentication: a local process that sends those headers can decide approvals. Run only trusted agents on the host and restrict console access with tailnet ACLs. Autopilot, an opt-in experiment that is off by default, also lets agents decide approvals of the operations the operator allows, over MCP (Autopilot).
• Local secrets. Secrets are encrypted with the local secret.key; secret APIs expose names only. A flat can read and return its own secrets, so deploy code you trust with them. Anyone who can read the data directory can recover those secrets.
• Back up your data. Immutable code versions are not data backups. Back up the data directory, including secret.key; see what to back up.

Read the design and trust model for the details.

Under the hood

Flats is one Go binary built without CGO, for macOS and Linux. It serves a web console, a CLI, an HTTP API and an MCP endpoint. There is no hosted Flats service. By default the console and the Local flat listener bind only to loopback (127.0.0.1:7878 and 127.0.0.1:7879), so other networks reach your flats only through the providers you turn on. Binding either listener to another address (host.console_addr, host.local_addr or --local-addr) changes that: anyone who can reach it can open the console or Local routes, including Private flats. See config.json.

Documentation

Get started	Build and operate
Install and upgrade	Runtime API reference
Connect an agent	Content types and lifecycles
Configure a host	Call external APIs
Run in a container	Design and trust model
Set up networking	Verification gates

Browse the complete documentation index for contracts, internal design and verification guides, and the product specs for what Flats is meant to do, including targets that are not fully implemented yet.

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MIT licensed · Releases · Issues