Vacant

Find an empty classroom near you at Ohio State, free for as long as you need it.

enesyilmazcode.github.io/Vacant

It is a web page. No account, no search box, nothing to sign up for. It finds you, asks one question, and hands you rooms you can walk to, nearest first.

One question.	The answer.	Where it is.

Yours for, not free until

Every other tool answers "is this room free right now". That is the wrong question, because the room is not where you are standing.

Vacant answers how long the room is yours once you get there. It takes the gap in the room's schedule, subtracts the walk, and leaves ten minutes at the end so you are not packing up while the next class files in. Walk time is straight line distance times 1.3 for the fact that campus paths bend, at 78 metres a minute.

Read the third row of the middle screenshot. Psychology Building 217 says free till 1:50pm. The next class in that room starts at 2:00pm, you are three minutes away, and 1:50pm is when you have to be packed up.

Tap it and the room screen says the same minute, then spells the rest out: Yours for 3h27 once you get there. The two screens agreeing is the point. They did not for a while: the room screen printed 2:45pm, the raw class start, handing back the ten minutes the row had already taken off (#77).

A row that says no class rest of today instead of a time means no class is coming at all, and the timeline behind it ends where the building locks.

Drag the sheet up for the rest.	Tap a room twice for its whole day, doors included.

Put it on your home screen

You do not have to. But it is built to be installed, and installing it is what makes it answer in a stairwell.

On iPhone, open it in Safari and tap Share, or ... then Share if your tab bar sits at the bottom, then Add to Home Screen. iOS 26 defaults to that Compact layout, which is why the app offers you both. On Android, Chrome has Install app in its menu.

Installed, the whole app is 70 KB of shell and 63 KB of schedule, gzipped, and none of it is fetched again to answer a question. Turn the network off, open it, and it still ranks rooms. That matters because the moment you want it most is the moment you are in a basement with one bar.

What it refuses to guess

Vacant reads the class schedule. A class schedule is not a reservation calendar and it is not a door. Three things are true and the app says all three on screen:

Doors get locked. This is the failure every other tool in this category ships with, and at Ohio State it is avoidable, because the Registrar publishes an open and close time per building per weekday. Measured against the committed index, 424 of the 425 rooms have no Saturday class at all this term. A tool that stops at the schedule calls all 424 of them free on a Saturday. 367 of those sit in a building the Registrar publishes as closed that day, and 57 are in a building that is genuinely open.

A door nobody documents is not offered at all. The Registrar's table covers 47 buildings. The index touches 46 of them, and 0 of the 425 rooms sit in a building whose hours are unpublished, because a room in one does not ship.

That used to be a label. 90 rooms rode along in their own tier reading hours not published, which was honest and was still the wrong answer: "here is a room, and we cannot tell you whether you can get into the building" is not an answer, and it cost four blocks of explanatory text across three screens to say. Over 5,040 ranked rows measured from four origins across a week, not one of them ever reached a top ten. They were paying for themselves in prose and returning nothing.

Clubs book rooms. A club meeting, a review session or a departmental event is invisible to every public source, so it is invisible to Vacant too. Every screen carries that caveat, and #26 is the plan to go and measure how often it bites.

How it works

Ohio State publishes, for every class, the room it meets in and the minutes it occupies. Nobody publishes which rooms are empty. But empty is the complement of busy, so the whole product is one inversion of a public dataset. A script walks the class API, drops everything that is not a real Columbus room, and writes a room-keyed list of busy intervals. The page downloads that file, subtracts today's intervals from the building's published opening hours, and ranks what is left by walk time. There is no server, no database, no build step and no dependencies.

Everything the page fetches to produce a ranked list is fourteen files, 472 KB, or 108 KB over the wire once gzipped. Measured with node:zlib over the tree as committed. The campus map is another 98 KB, 38 KB gzipped, and is warmed after the first answer rather than before it.

Where	What is in it
index.html	The whole shell. Markup and CSS, no framework.
js/app.js	Three screens in one sheet: the question, the list, one room.
js/engine.js	The ranking, and the formula that decides how long a room is yours.
js/map.js	The campus map, drawn as vectors on a canvas. No tiles, no key.
js/campus.js	Latitude and longitude into map grid space.
scripts/	The harvest, the inversion, and the screenshots.
data/	The committed artefacts the page reads.

Run it

git clone https://github.com/EnesYilmazcode/Vacant.git
cd Vacant
python3 -m http.server 8000     # or any static file server

Then open http://localhost:8000. It has to be served rather than opened as a file, because the page is ES modules and it fetches JSON.

npm test                        # node --test, 589 tests, no network
node scripts/shoot.mjs          # redraw docs/media from the real app

Stand somewhere else, on a different day

Open http://localhost:8000/dev/. It asks the two questions first: what minute, and where are you standing. Tap the campus map to drop a pin anywhere, or pick a building, or take one of seven one-tap jumps to Thanksgiving, finals week, Saturday at 3am or winter break. Then it hands off to the real app.

Once you are in, ?dev=1 or three presses of D opens a panel that changes the same two things without leaving the screen you are on.

It is not a preview. It moves the same clock every screen reads and the same origin the ranking measures from, then repaints through the same code path a duration chip uses, so the answer on screen is the answer a student would get. The readout at the bottom of the panel says whether the clock is live or simulated, and it says which rooms came back and why the app refused if it did.

js/dev.js is loaded on demand and is not in the service worker's shell list, so a phone that never asks for it never downloads it.

Rebuild the data

Nothing here needs a key or an account. Each of these takes --dry-run.

node scripts/fetch-buildings.mjs        # OSU's GIS layer  -> data/buildings.json
node scripts/fetch-campus.mjs           # campus polygons  -> data/campus.json
node scripts/fetch-building-hours.mjs   # Registrar table  -> data/buildings-hours.json
node scripts/fetch-rooms.mjs 1268       # the class schedule -> data/harvest-1268.json.gz
node scripts/build-index.mjs 1268       # invert it        -> data/rooms-1268.json

The harvest itself is not committed, because it is regenerated weekly, so a fresh clone has to run fetch-rooms before build-index. One pass over the schedule is 136 requests against content.osu.edu, sent at about three a second. The committed Autumn 2026 harvest took four passes and 545 requests, because paging that API is not deterministic: the harvester repeats until two passes in a row turn up no meeting in a room it has not already seen. Pass two found thirteen of them. data/harvest-1268.manifest.json records what every pass saw.

data/raw/1262 and data/raw/1264 are committed and must stay. Those terms have already left the API and cannot be refetched at any price.

Not built yet

• The list is a room list where it should be a place list. Forty rows came back across thirteen buildings, and one of them took six of them. #62.
• Nobody has walked to a room the app called free and checked. That is the measurement the whole thing rests on and it has not been taken. #26 is the walk, and spikes/walk.html is the checklist to walk it with.

Roomix

Roomix is the incumbent at Ohio State and deserves an honest description. It is a maintained three platform product: a Flutter app with iOS and Android builds, a backend, accounts, bookmarks, themes, a nearest facility button and a vacancy search. Anyone calling it a toy has not looked at it.

Two differences are measurable rather than matters of taste. Both were taken off its own API and its own compiled bundle on 2026-08-26.

It downloads about 3.3 MB on first launch. Its API is eleven static JSON files and courses.json alone is 2.4 MB.

It has no building hours. Grepping the bundle for "building hours", "holiday" and "final exam" returns nothing, and api.roomix.app/hours.json is a 404. Its vacancy search also needs a building selected first and then stops at a 200 metre radius from it, and it prints raw metres rather than walk time.

The full teardown, with the commands, is in docs/research/prior-art.md. It also corrects an earlier draft of this README, which said Roomix was organised building by building and ignored the clock. Both halves were wrong.

Docs

• docs/BACKLOG.md is the thirty issues, in order.
• docs/DECISIONS.md is append only, and records what each decision was made against and which measurement settled it.
• docs/research/ is the measurement itself: the live API, OSU's GIS server, the Registrar's table, Roomix's bundle.
• docs/BLUEPRINT.md is the design note this README used to be, kept whole, with the places it turned out wrong marked at the top.
• scripts/shoot.mjs regenerates every screenshot above from the real app, on a pinned clock and a pinned location, and refuses to write a frame of a screen that has not stopped moving. Re-running it on an unchanged tree writes the same five files. It also writes down what each screen said, in docs/media/frames.json, and a test holds the alt text above to it.

Licence

The code is MIT, in LICENSE.

The data is derived from Ohio State's own public services: the class schedule at content.osu.edu, the building layer published by OSU Facilities Information and Technology Services GIS, and the classroom pool schedule from the Office of the University Registrar. Each file in data/ carries its source and attribution inside it. Vacant is not affiliated with Ohio State. How that gets stated on the site is #25.