bitCaster 101

What is bitCaster?

bitCaster is a prediction market platform built on Bitcoin and Cashu. You buy and sell tokens that represent outcomes of real-world events — elections, sports, weather, anything. If your prediction is correct, the price of your tokens rises; if not, it falls.

At its core, it is fully open-spec and open-source. No user information is stored on the server side. Your tokens are yours — stored locally in your browser, settled instantly over Lightning or Cashu.

For an overview of Cashu itself, see the Bitcoin Design guide on ecash.

What you can do

Trade anything, any way you wish

Browse existing markets or place limit orders at any price. Markets can be binary (Yes/No), categorical (multiple outcomes), or even two-dimensional. You trade using Bitcoin via Lightning.

Categorical markets show primitive outcome books such as A / Not A, B / Not B, and C / Not C. Under the hood, settlement can still lock complementary multi-outcome legs such as B|C, but users trade through the primitive book labels. The first release supports markets with up to 8 outcomes.

Create your own market

Anyone can freely create a new market. Define the question, the possible outcomes, and the resolution criteria. There is no gatekeeper deciding which markets are allowed.

Become an oracle

In prediction markets, the value of a token depends on what actually happens in the real world. An oracle is the referee that determines that real-world outcome — which can sometimes be ambiguous. Anyone can become an oracle. The oracle is designated when a market is created and cannot be changed afterward. bitCaster’s protocol is designed to make oracle fraud as difficult as possible. See Resolution for details.

When a market’s oracle key is a Nostr public key, you should audit the oracle yourself before trading. Copy the market’s oracle npub from the market detail page and check that identity’s history and credibility in your preferred Nostr client.

Become a token issuer

Any user can run their own Cashu mint to issue prediction market tokens. The mint software is open-source, and the protocol specification is public. Multiple independent mints can coexist, each serving different communities or markets.

How it works

Every market outcome has a corresponding token. The price of a token reflects the market’s collective estimate of how likely that outcome is. The trade ticket asks for shares, not sats: if a market’s share value is D base units, buying n shares at price k costs n × k base units before the listed fee rows and pays n × D base units if that outcome wins. For example, in a market where one share is 100 sats, 50 shares at price 30 cost 1,500 sats before fees and pay 5,000 sats if they win.

When the event resolves, winning tokens are redeemable for their full share value, and losing tokens become worthless. Throughout this process, nobody — not even the token issuer — can know who holds which tokens or how many.

Your assets, your responsibility¹

Your tokens are just signed data. They live in your browser’s local storage, not on a server.

This means the server holds as little user information as possible. There is no account to create, no password to remember, and no personal information to hand over.

This completely eliminates risks such as personal information leaks or having only specific individuals’ assets frozen.

In return, like any other cryptocurrency wallet, you are responsible for managing your own keys. Back up your 12-word mnemonic and keep it safe.

When you start trading before completing setup, bitCaster can create a local wallet and a Nostr signing key for you. These are separate secrets. Back up both the wallet recovery phrase and the Nostr secret key shown in the app. If you already use a Nostr account, connect it instead of generating a new one.

Market detail pages

The market chart shows recorded trades for each primitive outcome. If only one outcome has traded, only that line is shown; bitCaster does not invent prices for outcomes that have not traded.

Trade comments are optional and public inside bitCaster. A comment is shown only after the attached order produces a settled trade, so the comment feed is limited to verified traders for that market. P20 comments are not published to public Nostr relays.

Getting started

Ready to try it? Head to the bitCaster app to start trading.

Note that ecash tokens are not strictly self-custodial. See https://iscashucustodial.com/ or https://bitcoin.design/guide/how-it-works/ecash/introduction/, https://stacker.news/items/793450 for details. ↩