I love TTRPGs. The storytelling, the improvisation, the moment when a table really clicks. However, I've only recently started GMing, and I love it.
But I also noticed something odd:
GMing is a performance role, and we’re expected to perform… without ever really being able to rehearse.
Actors rehearse. Musicians rehearse. Developers practise in sandboxes.
Game Masters? We just… show up and hope for the best.
That gap is why I built GMprentice.
Prep ≠ Practice
There are plenty of tools for GMs:
- Worldbuilders
- Encounter generators
- NPC name generators
- AI tools that spit out lore or dialogue
They’re all about prep.
But prep doesn’t teach you how to:
- Handle players going off-script
- Make rulings under pressure
- Manage spotlight and pacing
- Recover when an encounter falls flat
- Improvise when the party surprises you (which they always do)
Those are performance skills, And performance skills need practice.
The Real Problem: There’s No Safe Place to Fail
Most GMs I know don’t struggle with rules knowledge.
They struggle with confidence.
You can’t really practise:
- Emotional scenes
- Awkward rulings
- High-stakes moments
…without real people at the table, and failing in front of friends can feel awful.
So most of us just learn by doing — publicly, imperfectly, sometimes painfully.
I wanted a private, judgement-free space where GMs could practise first.
Why AI (and not just “ChatGPT for D&D”)
GMprentice isn’t a single chatbot.
The core idea is:
Simulate a party, not an assistant.
That means:
- Multiple AI “players”
- Distinct personalities and playstyles
- Disagreements, misunderstandings, bad ideas
- The kind of chaos that makes GMing… GMing
The goal isn’t to generate content for you.
It’s to push back, derail plans, and force you to react.
In other words it is a sandbox for training, not shortcuts to running a campaign.
What GMprentice Is (and Isn’t)
It is:
- A rehearsal space
- A sandbox to test encounters, rulings, and roleplay
- A way to build confidence before game night
It isn’t:
- A replacement for real players
- A replacement for the real creativity and art which is created in a real session
- A rules engine
- A content mill
If anything, it’s closer to a flight simulator than a writing tool.
Building It as an Indie Maker
From a technical perspective, the interesting challenge wasn’t “AI output quality”.
It was:
- Maintaining consistent personalities across multiple agents
- Balancing unpredictability without turning things into nonsense
- Making failure feel useful, not frustrating
- Keeping the GM firmly in control
I’ve been deliberate about avoiding the trap of “AI does everything”.
GMprentice works best when it resists you a little.
I built this app using Cursor, with extensive use of GPT 5.2 in 'Plan Mode' in Cursor, and Opus 4.5 for implementation and iteration of features.
I made extensive use of the Cursor Browser feature to work on finer details of styling and layout, with implementation assistance from Opus 4.5 working as a pair programmer.
This is the first time I've truly been shocked by coding LLMs. GPT 5.2 was planning for edge cases and scenarios that I had not initially considered and that would've only emerged in end-to-end testing. Opus 4.5 implemented features and styling changes almost flawlessly. The only major missteps were around Auth0 configuration and creating a middleware.ts instead of the newer proxy.ts expected in a NextJS 16 app.
This was a genuinely awe inspiring build, and I urge anyone cynical about AI coding agents, or who doesn't believe in their abilities to give them a try. You won't be disappointed.
I have also found the cognitive load of building an app like this is like nothing else I have experienced. I'm no longer laser focused on styling and feature execution, but I'm thinking about the core user experience more, I'm thinking about user journeys, conversion opportunities, and product vision more than nuanced detail which is really just noise. Using LLM coding agents this way frees you and empowers you to ship faster than ever, and deliver real production code that without LLM involvement - I probably wouldn't have had time to build something like this.
Why I Think This Matters
Tabletop RPGs are growing faster than ever.
More people want to GM — but GMing is still intimidating.
If we want more confident, inclusive, creative tables, we need better tools for learning the craft, not just preparing notes.
Practising privately shouldn’t be a luxury.
It should be normal.
What’s Next
GMprentice just launched, and it’s very much a work in progress.
I’m especially interested in:
- Feedback from experienced GMs
- How different playstyles feel in simulation
- Where AI helps — and where it absolutely shouldn’t
If you’re curious, you can check it out here:
👉 https://gmprentice.app
And if you’re a GM:
What’s the one thing you wish you could practise before a session?
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