Call of Cthulhu 7e
An AI Keeper's assistant for Call of Cthulhu 7e
The CoC7 system already rolls your percentile checks, offers the push, prompts you to spend Luck, and takes Sanity off the sheet for you. None of that is the hard part of running horror. The hard part is the handout that has to land on the right beat, and an investigation that has to stay coherent for as long as the campaign runs.
What is left once the dice look after themselves
Percentile checks at Regular, Hard and Extreme. The push button on the roll card, and the prompt to spend Luck when a failure lands one point short. Sanity checks that roll the loss, watch the daily limit, and set the insanity status on the token. A Bout of Madness drawn from whichever table you pointed the setting at. Chases with a sheet of their own. CoC7 does every bit of that by itself, and none of it is Familiar's business.
What that leaves is the Keeper's other job. Chaosium's own advice for Keepers names three parts of it outright: preparation, the non-player characters, and the props. Not one of the three is a dice problem. Give Familiar the scenario you imported and it reads the journals in your own world, so the location description arrives as you wrote it, the handout lands at the moment you planned for it, and the witness has the reason to lie that you gave him.
Atmosphere is the part Foundry still makes you build by hand. Chaosium's canvas tools can dim a light, play a sound, or reveal a map note, but each one is a region behaviour you attach per scene, wired to document ids and permissions, and only a GM can set it up. Familiar takes the same request as a sentence: "kill the lamps in the library, bring the rain up, hold it there until they leave".
- Lighting, weather and the ambient track set from one sentence, with no region behaviour to wire per scene
- Witnesses voiced in turn, each wanting something different and each willing to lie about it
- A journal entry written up after the session, so what the party learned stays searchable instead of living in your head
- The clue thread carried between sessions, kept in your own world rather than in a context window
- Handouts and journal pages read back as you wrote them, not paraphrased into something safer
What a Keeper is doing while nobody is rolling
These are the jobs between the dice. They are also the ones that decide whether the evening lands.
- A campaign like Masks of Nyarlathotep ships forty-five clue handouts, and the one you need now is the one you cannot lay a hand on
- Four witnesses in a single evening, each of whom has to sound like a different person and lie in a different direction
- Session nine, and a player asks precisely what the antiquarian said about that seal back in session three
- The room has to feel wrong before anybody thinks to roll Spot Hidden, and it has to feel wrong in specifics rather than adjectives
- A Sanity roll fails and the table wants to know what they saw, put into words that earn the loss
One ask, and what Familiar does with it
"They reach the shipping office after dark. Set the scene, and give me the night clerk." That one request reaches for four different things, and not one of them is a die.
Familiar reads the journal page you wrote for that location and narrates it as written. It sets the lighting and brings up an ambient track. It voices the clerk from the notes you left about him, with the want you gave him and the thing he would rather not say. Ask for a session note afterwards and it writes one into your world.
Every roll in that scene stays on CoC7's own cards: the percentile check, the push, the Spend Luck prompt, the Sanity call. Familiar does not reach for any of them. What it covers is the prep you would otherwise be doing at two in the morning.
Install Familiar from Foundry's package browser, connect your assistant, and it is at your Call of Cthulhu 7e table.
It arrives already speaking Keeper
On a CoC7 world the vocabulary is right from the first request. Investigators, not characters. The Keeper, not the DM. A pushed roll, Bonus and Penalty dice, a Bout of Madness. Ask a rules question and it looks in the compendium and the journals your world actually has, then leaves the call where it belongs.
The starter below then sets the table culture, and it is not shaped like the others in the set. Where they hand rules adjudication to the game system, this one points it at the Keeper and leaves it there. That is an accurate description of this game, and once you paste it in, it is the brief Familiar works from.
The starter leaves two slots deliberately blank, era and tone, because a 1920s Arkham game and a Pulp Cthulhu game want very different things out of the same scenario.
Where the rules engine stops
On Call of Cthulhu 7e, Familiar runs everything around the rules, and the rules are the one thing it does not touch.
Refereeing the rules is D&D 5e (2024) only. In combat the tracker, the turns, and the tokens still work; the rulings stay yours.
One setting to change: turn the combat auto-pilot off in Familiar's settings. It drives NPC turns through the 5e engine, so it does not know your system; the monsters' turns stay yours to run. Playing solo, that is the part you will feel.
This table is read from Call of Cthulhu 7e's own data model and Familiar's shipped code. It has not yet been run at a live Call of Cthulhu 7e table, so nothing here is described as observed.
| What you are asking for | On Call of Cthulhu 7e |
|---|---|
| Story, NPCs, scenes, audio, memory | Yes, all of it: scenes, lighting, weather, audio, NPC voices, images, transcription, journals, campaign memory, and your own compendia |
| Reading a character | Your system's own sheet, passed through untranslated, with items grouped by their own type names |
| Hit points | Read from your sheet's own attribs.hp. Applying damage stays with your system |
| Refereeing combat | No. Call of Cthulhu 7e resolves it, and the rulings stay yours |
| Rolling initiative | Familiar declines it out loud and points at Call of Cthulhu 7e's own initiative, before anything touches the combat |
| Conditions | Can be toggled on a token from chat |
| Table Rules starter | Written for Call of Cthulhu 7e, offered first when Familiar sees your world |
| Foundry system id | CoC7 |
The starter your table begins from
Familiar carries a Table Rules field per world, under Settings, System Rules. Whatever you put there is appended to every request, and it reaches your MCP client too.
Call of Cthulhu 7e has its own starter, offered first when Familiar sees your world. It is a starting point rather than a ruleset: the terms, the table culture, and slots for your setting, your tone, and your house rules. Paste it, then cut what does not match your table.
We play Call of Cthulhu 7th edition. Use its terminology: percentile skill rolls, Sanity, Luck, pushed rolls, Bonus and Penalty dice. Players are investigators and the GM is the Keeper, who adjudicates all rules. Look rules up in this world's compendium and journals. Standing guidance: - Never hide a needed clue behind one roll. If a search fails, another skill, scene, or pushed roll can find it. - Treat a fight as a last resort that can get an investigator killed. Reward stealth, talk, or escape. - Call for a Sanity roll before you describe what set it off, so the table dreads the reveal. - Pace the dread with cryptic detail and keep the monster offstage until the fear is earned. - Hand players the letter, the clipping, the diary page and let them read it for themselves. - Honor the table's lines and veils; when a subject is off-limits, steer the horror elsewhere. - Run the prepared scenario, and when the notes are silent ask the table rather than inventing. Setting: [era and location, e.g. 1920s Arkham or modern day]. Tone: [e.g. slow-burn cosmic dread, or pulp two-fisted action]. House rules: - [rule] Never speak or decide for the investigators.
Two places it stops short on a CoC7 sheet
Both come from one thing: CoC7 keeps its pools under field names of its own, and Familiar reads the one it recognises.
- Hit points come back in the character read, at the path the table above prints. They do not reach the scene and token listings or the GM screen, which look for a different field name.
- Sanity, Luck and Magic Points arrive as raw sheet fields rather than as pools Familiar keeps an eye on. Nothing is watching your Sanity for you; the number that counts is the one on the sheet.
That is the safer of the two failures. These are the pools that kill investigators, and a tool that wrote to them from chat on the strength of an untested field path is the one that would deserve your suspicion.
The two-handed table this game is known for
Call of Cthulhu has been played one Keeper to one investigator for as long as it has existed, and the published solo scenarios exist for exactly that. It is also the shape where the work shares out worst. There is nobody else to voice the coroner, and nobody to hand the clipping to but the one player in front of you.
Hand Familiar the imported scenario, the journals, and a character the two of you built in a prep session, and it plays the Keeper's side of the evening around your rulings. The calls are still yours. The dice are still on CoC7's cards.
The parts that are the same everywhere
Connecting an AI, choosing a model, and what it costs do not change with your game system.
- Everything Familiar can doThe full tool reference. Everything outside combat refereeing runs on your system too.
- Connect Claude, ChatGPT, or GeminiThe connection steps, identical on every game system.
- Choosing an AI modelWhich model, and how much thinking headroom a hard scene needs.
- AI voices for your NPCsTTS setup and voice pinning, the same on every game system.
- Campaign memoryThe record and the recall, unchanged by your game system.
Call of Cthulhu 7e questions
Does Familiar referee Call of Cthulhu rules?
No. The rules engine is D&D 5e (2024) only, and CoC7 is left to do what it already does well: percentile checks, pushed rolls, Sanity, the combat cards. Your rulings as Keeper never get second-guessed.
Can it read my investigators?
Yes, in the shape CoC7 stores them: the eight characteristics, the hit-point pool at the path in the table above, and your skills as the items they are on this system, grouped under their own type names. It then describes the investigator back to you in those terms rather than translating them into another game.
Will it run a published scenario, or make one up?
It runs what you imported, and that is the whole design. The maps, the handouts, the NPCs and the journal pages are the source, and the starter tells it to keep to the prepared scenario and to ask the table when the notes fall silent. An original scenario off a blank page is the one thing it is not for.
Does it handle Pulp Cthulhu, or a Gaslight or modern era?
Yes, because the era is yours to set rather than something to detect. The starter keeps a slot for it, and what Familiar reads is whatever your world actually has installed. A Down Darker Trails table and a modern-day one get their own vocabulary out of the same starter.
Other game systems
- Pathfinder 2eThe system automates its own combat, and does it well. Familiar takes everything else: the story, the NPCs, the scenes, and a memory that outlasts the session.
- Savage WorldsOne set of rules and a shelf of worlds to run them in. SWADE keeps the trait dice, the action deck and the wound math; Familiar takes the world they happen in.
- Warhammer Fantasy 4eA setting people run for years, on a Foundry system that already counts everything the rules ask it to. Familiar works the other side of that: voices, scenes, and notes that still make sense forty sessions later.
Fourteen days free, and no key needed if you already pay for Claude, ChatGPT, or Gemini. Playing Call of Cthulhu 7e and want to try it? I'm Ryan, the person who built Familiar. The Discord is small, so come and tell me how it goes on your system.