Show HN: Have fun betting virtual (not real) money on predictions from HN users

150 points by rose_ann_ 6 days ago

I wanted to see how difficult it would be to build a web app using a sub-$300 android smartphone. Decided to build a fun predictions website where you could bet virtual (not real) money on predictions made by others, and also make predictions of your own.

Building it turned out to be considerably easier and more fun than I anticipated.

Primary tools used were:

# QuickEdit as the mobile code editor (Note: the free version of the QuickEdit app is riddled with ads, it shows an advert each time you close a tab, but it unfortunately had the best UI of the 3 or so Android code editors I tested. Ended up using NetGuard to block it from retrieving & displaying ads),

# PHP for the Backend ( custom PHP microframework I've used and built on over the past few years ).

# jQuery for the frontend js (cringing) - it appears I'm simply too lazy to learn React/Vue/et al. Every once in a while, I pick one of them to learn, but I always end up returning to jQuery - or time-permitting - amateur level vanilla JS.

# Bootstrap for the CSS - Battle-tested. For a purely backend dev with minimal design skills, good ol' Bootstrap (and in a growing number of cases, Tailwind) is always a life saver.

# Whole thing is hosted on 2 VMs (1 hosting the web app, and 1 hosting Redis & MySQL).

# As to the site itself, it turned out to be pretty cool to play around with. Go there, view the predictions, bet on the predictions you believe will come true, or against the ones you think will not. You get $50,000 to bet with (not real money). No signup is required to bet, but a quick signup is required to make a prediction. Hope you guys like it, and please be ruthless in telling me of any bugs you've found.

So go on here =>

And Have Fun!

vagab0nd 6 days ago

Interesting site. How do you decide on the result of a bet? Where do you get the truth? What if the bet is described ambiguously? Or worse yet, something like "This prediction will be false".

  • quickthrower2 6 days ago

    I think the "market creator decides" works really well for play money markets. doe this. The risk of a "rug pull" is often discussed when assigning probabilities, and you can see people's history to decide if you trust them.

    A good market will have a well thought out process of deciding the truth. For stuff where there is a betting market or money market, it is easy to refer to that. Otherwise for something like "Will Russia invade Ukraine", at the time the definition of "have they invaded yet" had to be figured out, especially as no one knew how far it would go.

    • kqr 6 days ago

      Picking your brain for a slightly related question: how would you propose setting the initial odds, assuming the market creator can also bet?

      • quickthrower2 6 days ago

        Big question!

        (And sorry I might have been confusing. I am not the OP or creator of the Show HN, but I jumped in and answered how I would do it)

        First decide if you want the bets to be taken by an algorithmic market maker (so anyone who wants to place a bet can place it, but they get slippage, like Uniswap) or an order book (more like you say "Ill bet $500 at 33%" an then someone else says "I'll take the other side", like Betfair)

        Let's assume you use a AMM. Then the way to do it is let the market maker pick the probability, and provide the initial liquidity to the AMM at those odds. So they are incentivized to get it right. To derisk them a bit (after all they are taking bets with the least information, right at market open) you give them commission or something like that on bets placed.

        These are complex decisions. went though various iterations. They are erring on the side of simplicity for new users, so they fix the odds. You don't get a choice, it is 50%. Because it is an AMM you quickly revert to the right probability. Of course, since you time the creation of the market you could make those correcting bets yourself just in time.

        • kqr 6 days ago

          Setting all initial odds to 50 % seems like a great way to get people to propose bets that are very likely or very unlikely, and then immediately correcting, as you say. What does do to prevent that?

          I like the idea of the market creator providing the initial liquidity in exchange for commissions, though I am concerned that would leave the AMM short on capital to satisfy everyone's transactions. Maybe. I'd have to run some of the calculations. I hadn't thought about this approach. Thanks!

          (I'm well aware you aren't the OP or anything, I just thought your comment was insightful so I took the opportunity. No regrets!)

exabrial 6 days ago

There is _literally_ nothing wrong with your javascript on the page, FYI. stick with your toolset.

  • algo_trader 6 days ago

    Sure, for an mvp. Quick and clean output

    But what happens as you start adding stuff. Toaster notification, user badges, swipe actions.

    I an not a JS expert, but it seems a modern library will have these built in ?

    EDIT: would be interesting to hear the original poster's opinion

    • jsty 6 days ago

      > But what happens as you start adding stuff. Toaster notification

      Sounds like an amusing corollary to Zawinski's law. "Every program attempts to expand until it can notify you your toast is done..."

      • exabrial 6 days ago

        Npm would be a 1000x increase in codebase size… for notifications.

    • kqr 6 days ago

      Not original poster, but I also sort of don't understand the question. You do what you would do to evolve any MVP: swap out one part at a time to something that scales better. It's just a frontend.

dvh 6 days ago

It doesn't allow making prediction to 2030 so I just leave it here:

I predict that by 2030 none of the top 10 US car manufacturer will offer self driving in their cars (except for simple autobreaking). Even those manufacturers that offer some self driving now will stop offering it by 2030.

  • sircastor 5 days ago

    I think it’s unlikely we’ll see level 4 driving in fewer than 10 years, and I don’t think we’ll ever see level 5. It’s a really hard 80/20 problem. I think most peeler are going to be pretty happy with what you can get in a lot of vehicles today.

    Disclosure: I worked for an Auto OEM but didn’t have any knowledge or communications with any folks working in the space.

  • kqr 6 days ago

    ...and how likely do you think this outcome is? 60 %? 90 %? Somewhere in between?

  • szemy2 6 days ago

    I'm interested in the argument for this!

    • dvh 6 days ago

      When your neighbor Joe in his 1987 Buick run over your cat, you know he has 2 mortgages on his house and wife with cancer. When a self driving car runs over your cat or ding your fence post, you will gladly sue the multi billion dollar company, just for the settlement money. It will unleash the neverending stream of lawsuits and companies will be forced to stop offering self driving or go bankrupt. Yeah, they can afford best lawyers, but not 500 new lawsuits every day.

      • szemy2 6 days ago

        There was a case with Ford in the 70s were they calculated that a retribution cost per person would be around 200k - calculated the likely effect of the cars busting into flames because they had an design flaw. They realised they are still better off than to recall all vehicles.

        As the story illustrates, there might be situations were expecteded litigation is worth it. I'm not saying this is morally right, but companies will try to maximize their profit anyway, even if there are (calculable) risks involved.

        In the case of self-driving this might mean being a profitable car manufacturer vs becoming a niche, enthusiast car producer for people who still enjoy driving as a leisure.

        Here is one of essay on this:

      • leononame 6 days ago

        Wouldn't car companies just lobby for some law changes that would make the "drivers" responsible rather than the manufacturers?

        Or alternatively, allow self driving only on highways and such, where it's much safer?

        I don't think progress is stopped that easily

      • 972811 5 days ago

        I'm not sure the capability for FSD will be ready by 2030, but I don't think these reasons are compelling. Insurance will solve these problems

armchairhacker 6 days ago

What if someone posts a very likely or unlikely bet (e.g. "the next Mega Millions numbers will be ..."? Can everyone bet $30,000 against and then everyone gets $30,000?

You may want a system where, the more skewed a bet is, the less money gets paid out by the majority side and more money gets paid to the minority. That way, bets like those don't really get you anything, unless you bet the unlikely case and win, then you get a well-deserved jackpot.

  • tlyleung 6 days ago

    A parimutuel system would solve this. When settling the bet, the pool of money is divided among those that backed the winning combination, in the ratio they contributed. You can also display the odds based on how much money is behind each combination.

    • quickthrower2 6 days ago

      You lot discussing this would get a kick out of:

      I wish I could post a link, but in their Discord they had some really interesting chats and I think they pretty much invented a novel AMM for this. They are open source, so you can take a look here:

      I forget whereabouts in that repo the algorithm is though but have a hunt!

      • akrolsmir 6 days ago

        Hey! Austin from Manifold here, thanks for the links! I wanted to note that our novel mechanism which we've termed "Maniswap" is indeed pretty cool, but for most intents and purposes a simpler Uniswap constant product market maker would already do quite well as a mechanism, with the advantage that it's really simple (explainable on the back of a napkin!)

        Happy to chat more about prediction markets/AMMs, feel free to reach out to

    • kqr 6 days ago

      One characteristic of a parimutuel system for a relatively illiquid market is that the odds can swing quite drastically whenever anyone bets. In fact, even the amount one person bets is going to affect the odds they will get, so you need to display a table of odds for various bet sizes.

      This may or may not be a problem, but I've found it requires more... infrastructure (notifications etc) for people to avoid being confused by it, and give people a chance to withdraw their bet if the odds are no longer favourable (alternatively put in stops, but that also complicates the system.)

    • armchairhacker 6 days ago

      The issue is that this discourages popular bets, not just heavily-biased ones.

      If you divide by ratio, and add a fixed number (e.g. 2) to the "for" and "against", there aren't really false positives, and true negatives (e.g. a reasonable bet where people just happen to all bet one side, or a biased one that doesn't get much attention) are unlikely - unless there are too many bets or people are gaming the system, that is.

      • oehpr 6 days ago

        I don't think I understand.

        This pari-mutuel system (I always knew the system but did not know the name) seems near canonical to me. And the incentives seem clear cut. It seems to me that if you feel the odds for or against any prediction are wrongly calculated, then if you submit money to push those odds towards the correct ratio, then you should, on average, expect a return.

        ... I maybe should actually run simulations to check that, that's just what my intuition is telling me as to how it would work.

        I'm trying to understand what you are proposing and the motivations for it.

        By ratio, I assume you mean the ratio of the pool for and the pool against? So if prop A has $100 and prop B has $10, then the ratio would be 110/10, or 11:1. So your procedure would be to add a fixed number to this? Either 112/12 or 13:3? or perhaps you meant Prop A $100/(110/10)+2 and Prop B $10(110/10)+2

          So Prop A is ~11.1
             Prop B is  ~2.9
        Am I understanding this right? What do we do with these numbers?
      • danielmarkbruce 6 days ago

        This assumes no one is trying to make money. In practice, this is virtually never the case.

  • rose_ann_ 6 days ago

    That's a pretty good point, though in this case the 'winnings' are simply a fixed multiple of the virtual amounts bet.

  • kqr 6 days ago

    A quick way out of this issue is to ask users not for how much to stake, but how confidently they believe something to be true, and then reward/penalise based on a score function derived from this and the actual outcome.

aliljet 6 days ago

I can't not make this joke: Where do I send my BTC?

aoeusnth1 6 days ago

Is there a good reason to use this over Manifold (

  • c0balt 6 days ago

    The difference afaict is that Manifold both requires a google account and is effectively just using cents as an abstraction over USD. In comparison the bets in the submission are "truly" based on virtual, nin-exhangable money. Additionally, the submission is focused on HN in comparison to general bets like Manifold.

    • remram 6 days ago

      You can't get the money out, it all goes to charity. So while you're not betting free money, you are not betting your money either, it is consumed before you bet either way.

  • glotchimo 6 days ago

    Seems like Manifold requires a Google account which is definitely a mark against it for many

echelon 6 days ago

This is awesome! Kudos (no pun)!

I'd really like to wager real money. Due to gambling laws, I'd be fine if this went to charity, in a similar vein to longbets.

It's more about vision and narrative than winning money, anyway. Building esteem for sometimes contrarian viewpoints. (If you can predict where the world is moving, you can make money on that regardless.)

An internet track record would be amazing.

habibur 6 days ago

Order by most active bets at the top.

Right now the page starts with dead claims and you find pretty active and good ones while scrolling down.

IIAOPSW 6 days ago

I predict this platform of yours will still be up and running in a year from now.

alwillis 6 days ago

Can't count the number of times I've wanted something like this for Hacker News!

There have been quite a few hot takes (especially about Apple) where I would have bet against that person's prediction happening. Glad it's an option now.

euphetar 2 days ago

No way to assign probabilities? I prefer metaculus

sc90 6 days ago

Consider letting users add an explanation for each prediction so that we know the reasoning behind it.

pbhjpbhj 6 days ago

It's this just mining HN hive mind for "insider" information?

  • quickthrower2 6 days ago

    The insider information being the wisdom of the crowd. "Outsider information" would be a better description.

  • giansegato 6 days ago

    even if it was, everyone would benefit from the information (it being public)

algo_trader 6 days ago

Interesting. Why a 300$ phone?

Can u share how long it took to build and what is your day job ?

  • rose_ann_ 6 days ago

    Took roughly 2 weeks from start to finish. Work as a web dev in an accounting firm. As to the choice of the phone, got a Samsung Galaxy A23 on a while back and decided to use it to build a site

    • quadrature 6 days ago

      Now you have a second job updating the prediction outcomes :P. I was thinking it would be cool to sync them from github so folks could contribute an outcome.

      • rose_ann_ 6 days ago

        Lol, a second job? I sincerely hope not.

        I don't think the site'll garner much interest though. Betting virtual money doesn't really seem like a mainstream activity.

        Just wanted to put it out in the wild and get critiques.

    • olalonde 6 days ago

      Did you type the code on the phone's touch screen or using an external keyboard?

      • rose_ann_ 6 days ago

        I used the phone's touchscreen

        • nnoitra 6 days ago

          This may seem like a dumb question but why not use a laptop?

          • yjk 5 days ago

            From the OP:

            "I wanted to see how difficult it would be to build a web app using a sub-$300 android smartphone"

            I guess a fun challenge of sorts.

oumua_don17 6 days ago

I predict that your site will be renamed as HNLadsBroke in 2023!!!

hathym 6 days ago

It would be more fun if you can bet your real HN points :)

texaslonghorn5 6 days ago

if I click "View the Latest Predictions & Bets on Kudotap" on the homepage and then go back to the homepage, the button is unclickable the second time

demarq 6 days ago

This is a banger!!

I already know I’m going to like it

jtvjan 6 days ago

My preferred way of editing text on Android is to run Vim in Termux. If there's a terminal editor that you like (nano, emacs, joe, ed are all available too), try running it through there.

kaputmi 6 days ago

Without odds/probabilities this is much less interesting!

codetrotter 6 days ago

> Please fill out the 'Last Name' field (ensure it contains a least 2 characters (and does not contain any unusual special character)).

Please allow a wide range of Unicode characters. I am not able to sign up, because the site does not allow me to type my last name, it seems.

The letter “ø” is not an unusual special character..

  • cbhl 6 days ago

    Requisite pointer to "Falsehoods Programmers Believe About Names" ( from 12 years ago; use HN search if you want to see the more recent threads).

    If you've ever seen "FNU" as an Uber driver's name, that's a consequence of the _US gov't_ enforcing rules like this; it stands for "First Name Unknown".

  • shakna 6 days ago

    Also, just because it's a pet peeve - Last and/or Family names are not universal. Plenty of people with only one name.

  • michaelnoguera 6 days ago

    Friendly reminder that if op decides to allow more special characters in the name fields, they should check it does not open a stored XSS vulnerability. (Names are displayed to all site viewers on the predictions page.)

  • laserbeam 6 days ago

    Normally, that's a good idea. But based on OP's description this is a prototype or exersice in building /delivering an mvp. I don't feel that full unicode support is usually part of an mvp.

    • kqr 6 days ago

      I agree, but I also think it's a shame, because we should have libraries that make Unicode easy at this point.

sshine 6 days ago

Behavioural economists as well as poker players know that people make very different decisions when the money is real. The psychology is different.

  • Tenoke 6 days ago

    While generally true, for what is worth the recently popular play money prediction site Manifold Markets, as well as the general predictions site Metaculus both seem to do well and reflect what you see elsewhere quick.

  • leobg 6 days ago

    Kant knew this, too:

    > The usual touchstone, whether that which someone asserts is merely his persuasion — or at least his subjective conviction, that is, his firm belief — is betting. It often happens that someone propounds his views with such positive and uncompromising assurance that he seems to have entirely set aside all thought of possible error. A bet disconcerts him. Sometimes it turns out that he has a conviction which can be estimated at a value of one ducat, but not of ten. For he is very willing to venture one ducat, but when it is a question of ten he becomes aware, as he had not previously been, that it may very well be that he is in error. If, in a given case, we represent ourselves as staking the happiness of our whole life, the triumphant tone of our judgment is greatly abated; we become extremely diffident, and discover for the first time that our belief does not reach so far. Thus pragmatic belief always exists in some specific degree, which, according to differences in the interests at stake, may be large or may be small.

    • kqr 6 days ago

      There is a limit to this reasoning, though. As the wagered amount starts to become a significant fraction of your wealth, you should not make the bet even on very certain matters. Because that's the way you go broke in the long run, even on very sure bets. (Expose yourself to a 1 % loss often enough and eventually you will suffer it.)

      In other words, we might be "diffident" at the prospect of "staking the happiness of our whole life" but that does not mean that "our belief does not reach so far." It just means we are rationally evaluating the risk of ruin in the long run.

    • cookie_monsta 6 days ago

      Geez, people in the olden days took a long time to say simple things like "put your money where your mouth is"

  • phailhaus 6 days ago

    If you "charge" people by requiring them to spend time doing something in order to reset their supply, then that's sufficient to give the money some value.

  • netsharc 6 days ago

    OP should've called it Kudocoin and started with the price of, let's say, $2 for 50000 Kudocoins, [s]he'd be rich!

    Oh wait, it's 2022 and crypto has imploded...

    Edit: corrected gender, I don't know why your reply got downvoted to death, sorry OP.

    • rose_ann_ 6 days ago

      Building the site was more of an intellectual exercise to see how easy or difficult building using a low priced smartphone would be.

      P.S. OP's a "she"

TheCowboy 6 days ago

One ever underrated challenge with prediction markets is creating clear and concise rules for interesting questions, while the easy part is the tech powering the exchange.

For example, "James McIntyre is predicting that: There will be a global stock market crash in 2024." What constitutes a crash here? Or "Patricia Davenport is predicting that: An absolutely massive natural gas discovery will be made by a Southern African country before the end of 2023." has no clear meaning.

  • Waterluvian 6 days ago

    Didn’t this issue loosely arise with the 2020 US election and all the people trying to argue that the authority on who won was not legitimate?

    Most bets cannot be discretely quantified because there’s always something to argue about (such as the measurement methods). I think all it requires is for all parties to agree on an authority that makes the call.

  • soared 6 days ago

    Probably impactful for real money websites, but I can’t imagine anyone really cares for this fun money website where a good judgement can be applied pretty easily.

    • gpm 6 days ago

      It's obviously more impactful for real money websites, but realizing that two people mean different things by the same statement is pretty common. I think even fake money prediction markets are much more interesting if you largely avoid that.

  • bogota 6 days ago

    If you can’t measure it based on some agreed upon data source you can’t bet on it. Well you can but just have fun getting your money

mwint 6 days ago

Oh how I wish this existed a couple years ago, when everyone was making various shades of "the world is going to end" predictions. I would be a virtual billionaire!

  • madrox 6 days ago

    I actually built this as a startup two years ago. There's quite a few "prediction market" website out there which can be both for karma and real money. We tried to combine predictions with social media to allow users to build authority. The hard scale problem here is the reputation of the artibers of the challenge.

    We ended up pivoting when we realized to make this compelling at scale we'd essentially become a news site, and we didn't want to do that.

  • netsharc 6 days ago

    There were real life betting markets for all events, and people were even using it to predict the state of the world based on "wisdom of the crowd". But IIRC they mostly got outlawed, so they just exist for closed circles now.