Antigravity

Antigravity connects to ReUI through its MCP config, then you build UI by chat. ReUI requires an account, and Antigravity can do that two ways: the browser sign-in, which needs nothing but the server URL, or a personal token pasted into the config for setups that cannot open a browser. For the shared background (the tools, the plan limits, the sign-in flow) see the MCP server overview.

Connect ReUI

{
  "mcpServers": {
    "reui": {
      "serverUrl": "https://mcp.reui.io"
    }
  }
}

Headless and CI

For environments where no browser prompt is possible, create a personal token at Account → MCP (it looks like reui_pat_...) and send it as a Bearer header on the same entry instead of authenticating:

{
  "mcpServers": {
    "reui": {
      "serverUrl": "https://mcp.reui.io",
      "headers": {
        "Authorization": "Bearer reui_pat_your_token_here"
      }
    }
  }
}

Paste the token itself. Antigravity documents no variable substitution for mcp_config.json, and its own examples use literal header values, so a ${...} placeholder would arrive at the server as literal text and fail with a 401. Other clients differ on this, so do not carry the pattern across. This header is an alternative to the browser sign-in, not an addition to it. It is sent on every request and takes precedence over any OAuth credential the client has stored, so leave it out entirely on the sign-in path - otherwise authenticating appears to succeed while every call keeps failing.

Tokens expire after 90 days by default (30, 60, 90 and 180 are offered, plus No expiry for pipelines that cannot rotate). Nothing warns you beforehand, so an expired token simply starts returning 401 and has to be replaced.

The ReUI skill

Run the one-line installer in your project so Antigravity follows ReUI's build workflow:

curl -fsSL https://mcp.reui.io/install | node -

It writes the skill to .agents/skills/reui, which is exactly where Antigravity looks for workspace skills. With it in place, Antigravity knows the ReUI conventions and reaches for the right registry blocks, components, and icons as it builds. The same workflow is also available at runtime through the server's get_agent_skill tool, so nothing breaks if you skip the install.

Build with ReUI

Describe the interface you want in plain language and Antigravity pulls the right ReUI components, examples, and blocks from the registry, then wires them into your project.

Use ReUI to scaffold an admin app - the app-shell with a collapsible sidebar and top bar, and a dashboard page with stat cards and a chart.

Add a data-grid of orders with sorting, column filters, pagination, and row selection, wired to my /api/orders endpoint.

Build a multi-step "create project" wizard with the ReUI stepper and form components, with validation on each step.

Add a kanban board for support tickets with drag and drop, grouped by status, and a filters bar above it.

Unlock premium items

Free items (the 24 components and every c-* example) install with no license. To let Antigravity install premium blocks and icons too, grab a Pro or Ultimate license - one license unlocks the whole premium registry and removes the daily MCP request limit. Then add your key to the project - two quick steps:

REUI_LICENSE_KEY=your-license-key-here

{
  "registries": {
    "@reui": {
      "url": "https://reui.io/r/{style}/{name}.json",
      "headers": {
        "Authorization": "Bearer ${REUI_LICENSE_KEY}"
      }
    }
  }
}

That is it - Antigravity can now install any premium item the MCP returns, and free items keep working through the same config. See License Setup for the full guide, or compare plans on the Pricing page.

Troubleshooting

Most hiccups are the config shape or a stale credential. A browser sign-in can be renewed; a personal token has to be replaced.

• Tools missing, greyed out, or "not connected" - the server did not finish connecting. To fix it, confirm the reui entry uses serverUrl (not url or httpUrl), save the config, refresh the MCP servers list, then restart Antigravity.
• 401 and you signed in through the browser - your ReUI session expired. To fix it, open Agent Settings → Customizations, click Authenticate next to reui, and complete the flow again.
• 401 and you use a personal token - the token is missing, mistyped, expired, or revoked. Re-authenticating will not help, because the Authorization header is not a browser session. Generate a fresh token at Account → MCP and paste it into the header. The 401 body names which of the two it was.
• Requests hang or the session drops mid-build - long sessions can lose the connection. To fix it, refresh the MCP servers list and retry your last prompt.
• Sign-in appears to work but every call still 401s - check whether you have a headers.Authorization entry on the reui server. A configured credential is sent on every request and overrides the OAuth credential the sign-in stores, so while it is there opening Agent Settings → Customizations and clicking Authenticate cannot take effect. The two are alternatives, not layers: use the header only on the headless path, and remove it if you want the browser sign-in.
• "Your free ReUI MCP allowance ... is used up" in a tool result - the free plan has a daily MCP request allowance and today's is used up. It arrives as a normal tool result Antigravity shows you, not an HTTP error, so there is no status code to look for, and it resets at UTC midnight. For unlimited requests use a Pro or Ultimate license key, or a personal token from a licensed account, as your MCP credential, or wait for the reset.
• Every ReUI call fails and nothing asks you to sign in - the stored OAuth connection is dead (revoked, expired, or invalidated after a suspicious reuse), and the client is silently retrying a credential that can never work again. Account → MCP shows the connection as Disconnected when this is the case. Reconnect the same way as the 401 fix above; retrying without signing in again cannot recover it.