AGI IS HERE

AGI is here, and it runs in your browser. It understands commands like LOOK AT CASTLE, it draws in sixteen colours, and if you ask, it will put an alligator in the moat while you are standing next to it.

This AGI is Sierra's Adventure Game Interpreter, the engine behind King's Quest, Space Quest and Leisure Suit Larry, rebuilt from scratch and paired with an AI co-author. Play the classics from your own copies, or describe a new adventure and play it while an agent builds the world around you. Ask for changes mid-game: give the guard a different personality, add a puzzle, or turn the courtyard into a swamp. Everything the agent makes is a real AGI game that you can inspect, download and play again.

One brief, five models. Each castle is a real AGI picture drawn in vector commands, with a working moat, a hero and a game behind it, for between three cents and two dollars. From the Genesis benchmark.

Try it

Open agi.monotio.com and click Play now on Adventure Department, a three-room tutorial about how these games are made: you repair a picture, wake up a sprite and sort out a clerk's priority. You need no account, no API key and no Sierra files.

• Play your own Sierra games. Add game takes a ZIP or a game folder. The files stay in your browser's storage. The app recognises the edition, picks the matching interpreter and checks that the game opens.
• Watch a playthrough. Verified releases come with a recorded completion that replays on the real interpreter, keystroke by keystroke, on the game's own clock. Pause it, scrub the timeline, or Take control whenever you like.
• Rewind. Every session records itself, so you can go back to any earlier moment and carry on from there.
• Get help. Help is a short guide to playing, creating and managing your games, on the home screen and in a running game's Help menu. Each topic can open the control it describes.

The games it plays

These editions are verified in this interpreter. The PC editions are checked with recorded walkthroughs; the Amiga and Apple IIgs editions boot into their first room under their own interpreters.

Game	PC (DOS)	Amiga	Apple IIgs	Recorded walkthrough
King's Quest I	Yes			Full game
King's Quest II	Yes	Yes		Full game
King's Quest III	Yes			Full game
King's Quest IV	Yes			Full game
Space Quest I	Yes	Yes		Full game
Space Quest II	Yes	Yes	Yes	Full game
Police Quest I	Yes	Yes		Full game
Leisure Suit Larry I	Yes			Full game
The Black Cauldron	Yes			Full game
Mixed-Up Mother Goose	Yes			Full game
Donald Duck's Playground	Yes			One chapter
Gold Rush!	Yes	Yes		Full game
Manhunter: New York	Yes			Full game
Manhunter 2: San Francisco	Yes	Yes		Full game
Sierra AGI demo pack 4	Yes

A few things worth knowing:

• Walkthroughs are recorded on the PC editions and tied to the exact release they were captured on. The KQ1 completion proof shows how one is made and checked.
• Sound follows the machine. Amiga editions play through emulated Paula, the IIgs edition through its own Ensoniq wavetable instruments read from the game's files, and PC editions through the Tandy sound chip or the PC speaker, under Settings → Advanced… → Sound chip.
• Mouse clicks walk the hero on the Amiga and IIgs editions, as they did on the originals.
• The picture fills a 4:3 frame, the way a monitor of the day stretched the 320 × 200 screen. Settings → Original 4:3 turns that off for square pixels.
• Text uses this project's own 8 × 8 font in the original character grid. It covers English text and the box drawing the Sierra games print; other characters show blank.
• Fan-made games run too. If the app cannot tell which interpreter a game needs, it asks. Testing lists the exact editions and builds.

Bring your own copies of commercial games; they stay in your browser. No copies? Fans have made over a hundred free AGI games since the late nineties, collected on the AGI Wiki's fan release list and in the SCI Programming community's game list. Their content varies, as fan works do.

Make your own adventure

Pick a template or describe your own hero, setting and trouble, connect an OpenAI or Anthropic API key, and click Create adventure.

Template	Your predicament
Knight's Trial	Find three impossible treasures before the kingdom runs out of time.
Badge of Millhaven	A rookie cop discovers that procedure is easier to follow on paper.
Mop Jockey	The station needs a hero. It has sent the cleaner.
Polyester Nights	A middle-aged lounge lizard tries his luck for one more night.

The agent plans the world and builds the opening room: artwork, characters and game logic. When you walk into a room that is still unbuilt, play pauses while the agent writes it. Along the way you can:

• plan on the world map in Create's World panel: rename rooms, edit their briefs and pin notes the agent reads when it builds that part of the world;
• use Ask in Play for hints and questions that leave the game untouched, or Remix in Create to change it, including any game you imported;
• attach reference images for rooms and character sprites: the agent gets a thumbnail of each and looks closer at the parts it needs;
• preview the game's sounds as WAV clips.

Everything the agent writes is a standard AGI resource: logic, vector pictures, animated sprites, vocabulary, inventory and sound. The heroes above walk because the agent drew each frame of each direction, then compiled them into the same kind of view file Sierra's artists made:

An AGI room is also more than its picture. Behind it the game keeps a second, invisible layer: how far away each part of the scene is, and where the hero may and may not walk. The agent paints that layer too, so the knight walks around the notice board and the chest, stops at the water's edge and crosses by the drawbridge:

The agent checks its own work with rendered previews, compiler messages and playtests of its own. It can still get art, puzzles or writing wrong, so play it, and ask for revisions when something is off.

Your key, your provider, no server. The app talks to your provider directly from the browser. Your key is saved in browser storage and sent only to the provider you choose, along with the game content each request needs. Requests are billed to your account; each task starts with an estimated $5 budget that you can change. Each request extends the one before it, so the provider's prompt cache serves the conversation so far at its lower cache-read price. What the agent writes comes from your provider's model and is not reviewed by the app, so play a game through before you share it, especially with children. Security covers storage and data flow, and adventure briefs covers writing your own templates.

Edit every room by hand

A running game has two modes, switched in the top bar. Play is the game as its players see it. Create docks the tools around it: the world map and its rooms on the left, the assistant on the right. From a room in the World panel, its picture opens in Room Studio and its views in Sprite Studio. Room Studio and Sprite Studio need a larger screen than a phone; games play on phones too.

Left to right, top to bottom: Room Studio with the velvet rope selected, a test walk across the Sprite Lab, a proposal from Ask, and Sprite Studio on the waving robot.

• Room Studio shows a room's picture under three lenses: Art for what the player sees, Depth for what stands in front, and Walk for the lines that steer the hero. A scrubber replays the draw order command by command, the scene list names what the picture draws, and clicking a pixel shows the command that put it there.
• Editing works on items: click one to select it, or drag a box to select the items wholly inside it; drag the selection, or its points with the Point tool, nudge it with the arrow keys (a move stops at the picture's edge), change its colour, priority or draw order, duplicate or delete it. Alt+click, or Alt+Enter from the keyboard, adds a point to a selected line. A box, Shift+click, a group row or Shift+Alt+arrows select several items, which then move, copy and delete together as one step, so an imported bush's outline and fill stay together; Group (⌘G) names neighbours as one item without changing a byte, and Ungroup (⇧⌘G) splits it again. The tool rail draws lines, rectangles, polygons, fills and brush strokes at the scrubber's point in the draw order, and a ghost actor shows whether a character would stand in front of the scene or behind it.
• Keep saves the picture into the game. Each lens locks painting on the other planes until you unlock them, while a whole item moves with all its planes; every change can be undone, even after Keep, and leaving with unkept changes asks first.
• Test walks and doors live in the Walk lens. A test walk runs the real game in a throwaway copy and reports Reached, Blocked at whatever was in the way, the room it went to, or the message that stopped it. A goal on a door box or an edge walks through it (to the edge, then one step across), and a door a walk went through is marked tested. Door boxes and edge exits lead to other rooms; a door can follow its doorway art, so moving the art moves the door in the same Keep. Exits written in the room's own logic stay read-only. Right-click any spot and Play here jumps into the game there.
• Ask has your connected AI change only the selected items: "make this bridge walkable without changing the art". Attach reference art (a file, a drop or a saved image) and the AI can look at it while it works. Its proposal shows on the canvas, Before or After, with the changed cells outlined. The app's own checks hold it to the selection and the lens's locks, and Accept makes it one undo step.
• Sprite Studio edits a view's loops and cels. Open it from a room's views, the Resources tab or a staged character sheet, draw with the pixel tools, and reorder, duplicate and flip cels on a loops × cels timeline. The previews play the loop at the game's speed and stand it in a room at its real depth. Editing a loop that mirrors another makes it a separate copy, so fixing one facing leaves the other as it is unless you ask. Ask works here too, on the selected cel or its whole loop, with every other loop protected.
• Explainers sit beside the Studios' terms: each ⓘ says in one sentence what the control does and links to its Help topic. Each Studio shows a three-step tour the first time it opens, and Tour in its ? key list plays it again.

Save and share

Games, saves and history live in your browser. The game's own Save and Restore use the authentic AGI save format, with twelve named slots per game, and the app saves as you play, so Resume picks up where you left off.

Settings → This game	What you get
Export game…	A ZIP of the playable resources and public metadata: description, author, license and remix provenance.
Download game…	A ZIP of the game plus its authoring conversation, images, source descriptions, world notes, stored tests, map, session history, saved games and autosave.

Either ZIP opens again with Add game, in any browser. A game without a declared license keeps an unknown license in its exports; the MIT license covers this repository's own code and assets.

Thirty years later

Around 1996, Lance Ewing, Peter Kelly, Martin Tillenius and I worked on MEKA, an early fan-made AGI interpreter. I was Joakim Möller then. We traded discoveries about how Sierra's adventures worked.

On 3 September 2026, Greg Brockman closed an OpenAI briefing with “Welcome to the AGI era.” I took him at his word. With OpenAI's GPT-6 Astra in Codex, I went back to AGI to rebuild the engine, and to let an agent change the game while I was playing it. Now I can ask for an alligator in the moat, and the agent rewrites the game's own bytecode to put it there. Thirty years on, that is still a very cool thing to be able to do.

Peter Kelly's agi-re behavioral specification is the foundation of this independent implementation. It documents the formats, observable behavior and interpreter versions, and is published under CC0. Thank you, Peter.

As close to the originals as we could get

Every Sierra AGI game shipped with its own build of the interpreter, and the builds do not quite agree. On a PC, a wandering guard whose countdown runs out walks 256 more steps before he turns; on an Amiga he turns every 7 to 51 steps. Details like that decide whether a puzzle is fair, so the engine keeps them.

It starts from Peter Kelly's CC0 agi-re specification, a clean-room description of how AGI behaves. Where a game needs more than the specification says, or where builds disagree, the original interpreter's machine code was read and often run in isolation with controlled inputs, on PC builds from 2.089 to 3.002.149 and on the Amiga and Apple IIgs interpreters. The random-number generator alone was executed from ten original executables for all 65,536 of its states. Each finding is written down with its evidence and held in place by a regression test, and full-game walkthroughs of thirteen games replay on the engine keystroke by keystroke. Interpreter compatibility tells the whole story, from that random-number generator to the Amiga sound driver.

Under the hood, the engine is a TypeScript AGI interpreter with no framework and no runtime dependencies. It reads AGI v2 and v3 game files, including the Amiga and Apple IIgs layouts, and picks each build's behaviour through interpreter profiles. Games made in the app are standard AGI 2.936 bytecode with no custom opcodes. The engine runs in a Web Worker; the Vue shell adds a GPU-rendered CRT display and an in-game command line, while game text stays on the original 40 × 25 character screen.

How it's built

Coding agents build this project, alongside the agent inside it, and the repository checks the work of both.

• A written agreement. AGENTS.md holds the conventions, boundaries and method every contributor follows, person or agent: evals before features, and a check nobody has seen fail counts as a comment.
• Authority in code. The in-app agent can only call the tools on its session's allowlist, and what it writes still has to get past the assembler, the resource checks and the Studio's pixel-level validators.
• Mistakes become evals. A model error that recurs is stored as a bad case, like this one, and replayed offline on every check.
• One gate. npm run check runs the typecheckers, ESLint, ast-grep rules, knip, dependency rules, a design-token ratchet, a contrast test, the engine and app tests, and the stored evals. CI adds Playwright in Chromium and WebKit.
• Budgets. The startup path, from Home to a game's first frame, has a bundle budget that also keeps Studio and the AI stack off it, and interaction budgets bound boot long tasks and Studio frame and input times.
• Tests that are tested. Mutation testing, run on demand, checks that the picture and Studio kernels' tests catch deliberate bugs.
• Paid runs by consent. An eval runner calls a provider only with both --live and --budget-usd on the command line, and npm run eval:cache checks offline that every request keeps the one before it as its prefix, so the prompt cache keeps working.
• Measured models. The Genesis benchmark gives five models the same briefs and publishes every run, its cost and the game it made.

How it fits together maps the code.

Run it yourself

Install Node.js 22.22 or newer, then:

npm ci
npm --prefix app ci
npm run dev

Open http://localhost:5199/. The site needs a connection to load; it is not an installable offline app yet. Exported games play offline in any compatible interpreter.

Document	For
Interpreter compatibility	How the original interpreters behave and how the engine matches
Contributing	Development setup, architecture, checks and pull requests
Testing	Game fixtures, walkthrough proofs and compatibility checks
Hosting	Running your own copy and adding games to its catalog
Evals	Measuring authoring quality
Media gallery	Screenshots of the app, the Studios and the agent's tools
Security	Keys, storage and data flow

License

Created by Joakim Riedel and published by Monotio. The engine, authoring tools, browser shell and original project assets, including the Adventure Department tutorial, use the MIT license. Dependencies and imported games keep their own licenses; no commercial game assets are part of this repository. The icons are a hand-picked Lucide set (app/src/ui/icons.ts), with ISC and Feather MIT notices included in the build.