Gemini connects to Foundry VTT through Antigravity, and a free Google account is enough.

The route that adds nothing to your AI bill

Antigravity ships in two surfaces, and they share one MCP config file, so setting Familiar up in either leaves it sitting in the other as well. A Google account connects both, a free one included; the limits follow your plan, so Pro and Ultra lift the ceiling rather than unlocking the feature.

Familiar's wizard card writes the entry for either surface. Nothing on this route is typed by hand; what differs is where the entry goes, and the bullets below carry that. The check that proves the link waits at the end of this page.

• Antigravity CLI: install, sign in with Google OAuth, then run the setup command from the wizard. It adds Familiar to your Google MCP config beside whatever is already in there.
• Antigravity Editor: a separate desktop install, configured by pasting the same entry into its raw config. The desktop app takes the whole tool set from the first message; the standalone IDE opens on the core tools and pulls the rest in as the conversation asks for them.

The free tier is real, and it is also the smallest allowance on this page. A long night of heavy asking can reach the end of it, and the fix for that is a paid Google tier rather than anything on Familiar's side.

• Antigravity CLI and Antigravity Editor: the setup stepsThe click-by-click for both surfaces, plus what to try when the link will not take.
• Install Familiar in FoundryThe module goes into your world first. Antigravity has nothing to reach until it is there.

Snags only Antigravity has

Most of what breaks an MCP link is not Antigravity's doing, and those cases have a page of their own, linked below. What is left is short. Every entry on it sits between the install and the first answer.

• PowerShell says agy is not recognised, right after the install

  The window you installed from cannot see it yet. Close that window, open a new one, and type agy --version there; a version number means the install took. A Mac or Linux terminal behaves the same way.

• agy asks how you want to sign in, then will not give the window back

  The sign-in is a menu rather than a button. Pick Google OAuth, the first entry, press Enter, then open the URL agy prints in your browser. Once the browser says you are in, close that terminal window instead of pressing Ctrl+C, which does not reliably leave agy, and open a fresh one for the setup command.

• familiar is missing from /mcp after the setup command ran

  The command writes the file and prints nothing, so silence was the expected result. An older Antigravity build reads the previous config location instead, the antigravity folder under .gemini rather than the config folder; put the same entry there too. If you typed the entry by hand, leave out any type field, which Antigravity rejects.

• The tick beside familiar is green, and Foundry says Not running

  The tick is weak evidence. agy loads its MCP servers in the background and never checks on the process it started, so the tick can sit over one that has died; Foundry's own MCP tab is the honest read. Then ask agy for its version. Builds before 1.1.10 left the server process behind when a session ended, and an old enough leftover still holds the port against the new server. Update agy, end the leftover, and open agy again.

• The Editor shows no familiar under Installed MCP Servers after the paste

  The Editor reads that file when it starts. Click the refresh icon beside the list first, which re-reads it in place; on the standalone IDE that is Manage MCP Servers, then Refresh. If familiar still does not show, quit the Editor fully and open it again. Then start a new conversation before you ask anything.

• Your other MCP servers vanished from the file after the setup command

  The command only ever replaces the familiar entry and leaves the rest of the file alone. The one file it will not merge into is one it cannot read as JSON, and that one it copies to mcp_config.json.bak beside the original before writing. Open the .bak, fix what broke it, and paste your other servers back.

• The snags every client shares, answered onceThe browser choice, a hosted game, an antivirus in the way, a paste that will not take. One list, one page.
• Worked the list and still stuck?Bring agy's version and what Foundry's MCP tab says, and someone on the server will look at it with you.

The route with no agent app at all

Nothing gets installed on this route. You point Familiar at a Gemini model, hand it a Google API key, and the answers come back in a chat window inside Foundry, with Google metering what you use. It is the shortest setup on this page.

That window is also where Familiar's own conveniences live, the ones that need Foundry open in front of you. An outside agent has no way to reach them.

One Gemini-shaped detail, because it catches people arriving from another model. On this route you set the reasoning effort inside Familiar, and no Gemini family offers an off rung, so the lowest setting is the floor. A Gemini model always thinks a little before it answers.

• Install Familiar and connect your first modelWhere an API key goes, and what the settings tab looks like once it lands.
• Model tiers and the Thinking dialWhich Gemini to point at, and what the effort setting actually changes.

Which of the two suits your table

The fork is not about power. It is about where you want the assistant to sit: in a terminal or an editor beside Foundry, or in Familiar's own window inside Foundry. Answer that and the route picks itself.

• You already have a Google account and want no new metered spend: Antigravity.
• You want the whole setup done in a settings tab, with no second app installed: the key.
• You want live transcription, the combat auto-pilot for NPC turns on D&D 5e, or the model answering inside Foundry: the key is the only route that reaches those.

• Where the money goes on each routeA plan you already hold against a key metered per token, and which suits how often you play.
• Running the model on your own machineThe third answer to who pays, with no provider in the path at all.
• A different game system at your table?The hub for the systems covered so far.

What you bring, and what Gemini brings

The adventure is the part no machine made. Someone drew those maps, wrote that cast, and laid out the rooms and the journals. You import their work into your world, and Gemini plays from the pages in front of it.

That is also why the free route holds up. Your Google tier decides how much you can ask for in one evening. It does not decide whether the story is any good, because the story arrived with the module. What Gemini adds is the voice, the read on a moment, and the bookkeeping while you play.

• Journals & Notes
• Characters & Items
• Knowledge & Memory

• Everything Familiar can doThe full tool list by domain, if you want to see what Gemini can reach in your world.
• Getting a published adventure into FoundryHow to lay a module in as journals and sheets, so there are pages to run from.
• The rules I give my AI DMStanding house rules for the model at your table, free to copy and cut.
• How to play D&D with AIWhat playing this way looks like, from the first import to a live session.

Short asks to open with

One line proves the whole chain, and both Antigravity cards in Familiar's wizard end on it. Before you send it, check that the link is up on the surface you chose. In the CLI, type agy, then /mcp, and look for familiar listed as connected; the first time a Familiar tool runs, Antigravity asks for approval, so allow it. In the Editor, the list under Installed MCP Servers shows familiar with a green dot and its tool count, and the ask goes in a new conversation. If the answer names your world, you are through.

The four under it are short on purpose. A narrow question answered from one page costs a fraction of a wide one, and that is the habit to start with on the smaller allowances. Each ask reaches one of the three things named above: a journal page, a sheet, or what the campaign has been told to remember.

• Confirm the link

  Use Familiar's get-world-info tool

  Copy Confirm the link
• Play from one page

  Open the journal entry for <location> and describe what the party sees as they arrive, using only what is on that page.

  Copy Play from one page
• Find who carries what

  Which party member is carrying <item>, and how many do they have? Read it off the sheets.

  Copy Find who carries what
• Save a fact for next time

  Save this as a campaign memory: <what just happened>.

  Copy Save a fact for next time
• Ask what the campaign remembers

  What does the campaign remember about <NPC or place>? Look in the saved memories and the journals first.

  Copy Ask what the campaign remembers