What is a hackathon?

the short definition

A hackathon is a competition with a deadline. Organisers set a theme and a time limit, participants form teams, and every team spends that time turning an idea into something that runs. At the end each team demonstrates what it built, judges score the entries against published criteria, and prizes go to the strongest.

Four things make an event a hackathon rather than a workshop or a conference: it is time-boxed, work happens in teams, the output is something built during the event, and it is judged. An event missing any of the four is usually called something else on its own listing — a workshop, a bootcamp, a meetup — and this directory follows whatever the organiser called it.

what the word means, and how it is written here

“Hackathon” joins hack and marathon. “Hack” is used in its older engineering sense — solving a problem quickly and inventively — and not in the sense of breaking into systems. “Marathon” describes the format: one continuous, fixed block of time rather than a series of sessions. So the word literally describes a long, uninterrupted stretch of inventive building, which is what the event is.

Japanese writes it in katakana as ハッカソン, and the English hackathon appears alongside it on many listings. The two are the same word, and this site reads both: the search box matches either script, and an event is listed under the name its organiser gave it, in whichever script they used. Japanese has no spaces between words, so the matching that other editions do on word boundaries is done here by substring instead.

how a hackathon runs

The order is close to the same everywhere:

• Kickoff — the organiser sets out the theme, the rules, the judging criteria and the deadline.
• Team formation — people either arrive as a team or form one on the spot.
• Building — the bulk of the time, usually with mentors on hand.
• Submission — work stops at a hard deadline and teams submit whatever state their project is in.
• Demos — each team presents, typically in a few minutes.
• Judging and prizes — judges score against the criteria set at kickoff and announce winners.

the kinds of hackathon run in Japan

The one word covers several quite different events here, and working out which kind you are looking at tells you most of what you need to know before registering — who else will be in the room, how long you will be there, and whether anything is at stake beyond the prize.

• University and kosen hackathons — run by a laboratory, a student circle or a university's entrepreneurship arm, normally over a weekend and normally the largest by headcount. The University of Tokyo, Tokyo Tech, Waseda, Keio, Tsukuba and Osaka run their own, and the technical colleges (kosen) have contest traditions of their own. Campus events are where the beginner-friendly listings cluster.
• Corporate hackathons — a company sets a challenge tied to its own business and runs it over a day or two, sometimes with a cash prize and a recruitment pipeline attached. The telcos, the banks, the manufacturers and the platform companies all run them, and API- and SDK-themed “developer” editions are the visible ones.
• Government and civic-technology events — ministries, prefectures, municipalities and public research bodies run open-data and public-service hackathons, usually with a policy brief rather than a commercial one, often with a Code for community running the room.
• Community and startup hackathons — organised by a meetup group, a coworking space, an accelerator or a technology vendor. Usually shorter, usually free, and usually announced only a few weeks ahead, which is why a calendar is worth checking more than once.
• Game jams — the same format applied to making a game rather than an application, most visibly around Global Game Jam each January. “ゲームジャム” is the single largest filter term in this market after the head term itself, which is why it has a page of its own.

The name shifts with the subject matter. A hackathon over datasets is usually a データソン (datathon); one that stops at the idea and the pitch, with nothing built, is an アイデアソン (ideathon); and a weekend of building a game is a game jam. They are all the same shape — a brief, a clock, teams, a demo — and this site lists each under the name its organiser used.

// the formats named above are examples of the KINDS of hackathon run in Japan, described by what the format is rather than by any organisation's record. Nothing there is a claim about a specific edition, its dates, its size or its outcome — every event this directory lists has its own page, with the organiser's own description and a link to their listing.

how long they last

There is no standard length — the organiser sets it. Of the 10 hackathons listed on this site right now, 8 run inside a single day and 2 run across two or more. The longest currently listed is Tokyo AI (TAI) | OpenAI : 100-Hour Game Builder Challenge, which runs 7 days (11–17 Sep 2026).

The two shapes you will meet most often in Japan are the weekend build of 24 or 48 hours, which starts on a Friday evening or Saturday morning and finishes with demos on the Sunday, and the single working day, which is what most corporate challenges and community events run. Shorter events are built around a narrow brief you can finish in one sitting. Longer ones leave room for a bigger build and normally put food, sleep and mentor sessions in the schedule.

what it costs to enter

Nothing currently listed here charges to enter. 8 of the 10 hackathons listed on this site publish a free ticket, and 2 have not announced one yet. Where an organiser has published a figure it is on the listing, so you can check before registering.What a ticket price does not tell you is capacity: free events at universities and coworking spaces routinely cap places and close registration early.

do you need a team

Almost always, and the organiser sets the size rather than leaving it open — it is one of the first things stated on a listing, because it decides how you show up. The limits vary more than people expect, from a pair to a room, so read the one on the event you are entering rather than assuming. If you arrive alone, most events run a team-forming session at kickoff.

in person or online

Worth checking before you plan around one. Of the 10 hackathons listed here, 9 are in-person and 1 is hybrid, which still means a session you attend in the host city. Nothing on the calendar right now is online-only.The practical question here is rarely which city — the calendar is Tokyo's — but whether you have to be there at all, which is what the format filter answers.

where they happen in Japan

Overwhelmingly in the Tokyo metropolitan area. Right now 8 of the 10 hackathons listed here are in Tokyo, and the other 2 are split between Osaka. The 23 wards, Kawasaki, Yokohama, Chiba, Saitama and Tsukuba together carry nearly the whole Japanese calendar, so this directory does not split listings across city pages: everything in the metropolitan area browses under Tokyo, and each event page carries the exact venue. Osaka, Kyoto, Nagoya, Fukuoka and Sapporo keep their own name on the card. The one split that does carry information is in-person against online, and that is a filter on the homepage rather than a separate page.

In practice the venues repeat. 8 of the 10 hackathons listed here name one — Datadog Japan Office; HACK.BAR（ハックバー）心斎橋; Kawasaki, Japan; Osaka Innovation Hub; Plug and Play Japan; SivanS株式会社; Startup Island Taiwan — Tokyo Hub and 渋谷サクラステージ — and the other 2 give Japan without a venue. The addresses behind them sit in a handful of places: the Shibuya and Shinjuku coworking floors, the Marunouchi and Otemachi innovation bases, the university campuses at Hongo, Ookayama and Tsukuba, and Minato Mirai in Yokohama. Each event page carries the exact venue and address; nothing in the metropolitan area is more than about an hour away by train, which is why they all browse under one label. You can see every listing in one place.

the types you'll see listed

Hackathons are usually named for their subject or their audience. These are the filters this directory keeps, with what is on each right now:

ai hackathons

A listing appears here when the organiser describes the event around AI or machine learning — the theme it is judged on, the tools teams build with, or the problem set it hands out. (8 listed)

game jams

A listing appears here when teams build a game inside a fixed time limit — video games or tabletop, solo or team, from a theme or a constraint handed out at the start. (1 listed)

Events are also split by format — in person, online or hybrid. You can filter every listing by format from the browse section on the homepage.

who can enter

Hackathons are open to more than programmers: teams that win are usually a mix of engineering, design and someone who can present the idea clearly. Plenty of events are aimed squarely at people who don't write code, and say so in their own description. 1 of the 10 listed here is built around vibe-coding, no-code or agentic tooling by the organiser's own description, which is a fair part of why the format has stopped being a programmers-only event.

what you can win

Prizes are set per event and published on the listing. They are not always cash — mentoring, cloud credits, hardware, an incubator place and introductions are all common — and the amount varies enormously between a community jam and a sponsored event.

faq

find one to enter

This site lists every upcoming hackathon it can find in Japan, updated weekly. Browse all 10 upcoming events, narrow to ai hackathons or game jams, or browse every upcoming listing.

Running one? Submit your hackathon — free to list.