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.

Installing it is one command from Google, and then two things catch people out. On Windows, PowerShell will not see the agy command until you open a new window, so close the one you installed from. Signing in is a menu rather than a button: run agy, arrow down to the Google OAuth entry, and finish in the browser it opens.

A green tick next to familiar in Antigravity's /mcp list is weak evidence. The CLI loads MCP servers in the background and does not check the process it started, so the tick can sit over a dead one; Foundry's own MCP tab is the honest read. If the server keeps dying on start, ask agy for its version: builds before 1.1.10 leaked the old process, and the leftover holds the local port the next one needs.

• Antigravity CLI: setup is a command that merges Familiar into your Google MCP config rather than overwriting it, so any other servers you keep in that file survive. Then you sign in with Google OAuth.
• Antigravity Editor: a separate desktop install, configured by pasting into its raw config, and it reads that file only at startup, so quit it fully and reopen. It 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.
• Antigravity says connected, Foundry says not?Bring what agy reports for its version and someone will work it through 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 Foundry's own sidebar. 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.