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.

The browser serves casual participants and market creators. Professional and automated traders can use the CLI, daemon, and SDK. Every client uses the same CLOB and settlement protocol.

At its core, it is fully open-spec and open-source. Your live wallet and tokens stay local to your browser. The web app can store an encrypted recovery copy that the server cannot decrypt; see Encrypted wallet backup for its privacy boundary.

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) or categorical (multiple outcomes). The product uses sat ecash for ordinary wallet funding and msat conditional ecash for market positions. You can top up through a Lightning invoice or by pasting an existing sat Cashu token.

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.

Use the supported mint

The first release supports one Cashu mint operated by bitCaster. The app does not support selecting or using another mint. The mint software and protocol specification remain public.

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. Prices are shown as probabilities with two decimal places, such as 53.27%.

The trade ticket asks for whole shares and shows the cost before you submit. The breakdown separates Quote payment, Est. settlement fee, and Total, so you can see the order payment apart from the estimated mint fee. One categorical-market share pays 10 sats if it wins. Internally, categorical markets use msat collateral subunits with D=10000, so the smallest price move is 0.01%. For example, 50 shares at 30.00% quote 150 sats before any estimated settlement fee, and pay 500 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. The mint cannot selectively freeze an identified user’s ecash. It can stop service for everyone, so users must still assess the mint before they participate.

Your assets, your responsibility¹

Your tokens are just signed data. The live wallet database is in your browser’s local storage. The default web app also keeps an encrypted recovery copy whose contents the server cannot read.

This minimizes the wallet information held by the server. The encrypted-backup service can still observe limited account, size, and activity metadata. It cannot decrypt or spend your funds.

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 first open the portfolio page or try to trade, bitCaster asks you to set up a wallet. You can create a new wallet (auto-generated locally in your browser) or import an existing wallet using your 12-word recovery phrase. A Nostr signing key is also created or connected at this point. 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.

The order book shows asks (sell orders) above the spread and bids (buy orders) below it, with the best prices closest to the spread. Each row combines price, cumulative depth, and visual thickness. Longer bars mean more cumulative liquidity available at that price or better, normalized across both sides so you can compare bid and ask depth at a glance. Market cards and detail pages show Bot Budget for creator-funded AMM markets; this is the static budget deposited for the bot, not a live order-book liquidity number.

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. ↩