Guide
Play D&D with ChatGPT in Foundry VTT.
Connect ChatGPT to your Foundry VTT game and it runs the dungeon master's side of the table. ChatGPT reaches Familiar through Codex, the agent your plan already includes, so your subscription drives the game with no per-token bill on top. Or bring a key: paste an OpenAI API key into the built-in chat instead. Either way you talk to your game in plain language, and it runs the published adventure you brought.
Can ChatGPT run your Foundry game?
Yes. ChatGPT drives Familiar, the Foundry module that puts an AI on the dungeon master's side of the table. You ask in plain language and it acts in your world: it rolls initiative, plays the monsters, looks up a rule, voices an NPC, and keeps a record of the campaign. You stay the player.
What decides how well it plays is what you feed it. ChatGPT does not invent your campaign. You import a published adventure, the maps someone painted and the NPCs someone wrote, and it reads that work and runs the table on it, from a single scene to a whole campaign. The story stays the one you brought.
ChatGPT runs the adventure you imported. It does not improvise a plot from nothing, which is the line between Familiar and a weekend AI-DM app.
Connecting ChatGPT to Foundry
ChatGPT connects a step differently from Claude. There is no ChatGPT app to add as an MCP connector; you reach it through Codex, the coding agent OpenAI ships with a ChatGPT Plus, Pro, or Team plan. Codex speaks the Model Context Protocol, so it is the piece that talks to Familiar, driven by the same account you already pay for.
Two flavours of Codex work, the CLI and the desktop app, and Familiar's in-app wizard writes the config for whichever you use. The click-by-click for each lives in the connect guide, so this page does not restate it.
- Codex CLI: one command adds Familiar to Codex.
- Codex Desktop: the wizard writes the config block for you.
Playing D&D with ChatGPT
Once Codex is connected, you play by talking to your game the way you already talk to ChatGPT. Ask it to open the scene, run the fight, or catch you up on last session. It reads the situation, works the Familiar tools, and Foundry does the rest: a token crosses the map, a status effect lands, the right journal page opens.
The rules run in code, out of ChatGPT's hands, so a fight cannot be fudged; ChatGPT's job is the language and the judgement calls.
On a direct OpenAI key, the built-in chat gives you a reasoning dial too, down to the fastest off setting for quick lookups. Which model to pick, and how hard to let it think, is its own guide.
Combat & AIJournals & Notes
What ChatGPT costs to run
Codex or a key, and they cost differently. Drive ChatGPT over MCP through Codex on a plan you already hold and nothing is billed per token on top; you spend that plan's normal quota. Or paste an OpenAI API key into the built-in chat and pay per token for what you use. One thing trips people up: a ChatGPT plan and an OpenAI API balance are billed apart, so a subscription does not hand you API credits. You pick one route or the other.
Connect ChatGPT and play
Install Familiar in Foundry, connect ChatGPT through Codex or paste an OpenAI key, and import the first chapter of a published adventure you own. That is enough to run a session and see how it feels.
More in Get started
How to add AI to Foundry VTT
NewInstall Familiar, connect the AI you already pay for, and let it run the published adventure you import. The on-ramp to an AI co-pilot in Foundry.
Connect Claude, ChatGPT, or Gemini
NewConnect the Claude, ChatGPT, or Gemini you already use to your Foundry game, over MCP. No API key, no per-token bill, just the assistant you know.
Play D&D with Claude in Foundry
NewConnect Claude to your Foundry game and it runs the DM's side of a published adventure. Claude Desktop and Claude Code speak MCP, so your Anthropic plan drives it with no per-token bill.
Play D&D with Gemini in Foundry
NewConnect Gemini to your Foundry game and it runs the DM's side of a published adventure. Reach it over MCP through Antigravity on any Google plan, including free, or bring a Google API key.
Choosing an AI model
NewWhich model, and how hard should it think? A capable model with reasoning headroom is the second lever behind good prep. Turn thinking up for fiddly rules, down to keep replies fast.
The rules I give my AI DM
NewA copy-paste rules pack that makes any AI a disciplined Game Master. Roll only when it matters, run the adventure you prepared, never decide for the players. Every rule in it was paid for at a real table.
MCP vs API: which to choose
NewSubscription or API key? MCP subscription versus a pay-per-token key, and which is cheaper for how your table actually plays.
New to Familiar? I'm Ryan, the person who built it. The Discord is small and brand new, so if you join now I'll help you get set up myself.