# Solution

MindDuel is **trivia-gated PvP Tic Tac Toe on Solana**. Two players stake real SOL or USDC, then race to claim cells on a board. Every move requires a correct trivia answer. Wrong answer? The turn passes. Knowledge plus board strategy decides the winner.

The smart contract is the entire backend for anything that matters:

* It holds the escrow.
* It validates every move.
* It verifies the commit-reveal hash.
* It distributes the pot at settlement.

## The four pillars

### 1. Trustless escrow

Both players stake into a program-derived address (PDA). Funds can only leave through `settle_game`, `cancel_match`, or `resign_game` (and their USDC variants). Nobody — not the platform, not the developers, not the opponent — has a key that can move escrow funds outside those instructions.

### 2. Commit-reveal anti-cheat (no oracle needed)

The classic problem with on-chain trivia: how do you check the answer without a trusted server telling the chain "yes, that was correct"? Most games use a centralized oracle. MindDuel does not.

The flow:

1. The player picks an answer locally.
2. The client computes `SHA-256([answer_index, ...32-byte nonce])` and submits it on-chain via `commit_answer`.
3. After the commit confirms, the player calls `reveal_answer` with the raw answer and nonce.
4. The program recomputes the hash with `solana_program::hash::hash` and checks it matches the commitment.

The trivia backend never learns which answer the player picked, and has zero influence on whether a piece gets placed. The chain is the verifier.

### 3. Three live game modes

| Mode               | Twist                                                                                                             |
| ------------------ | ----------------------------------------------------------------------------------------------------------------- |
| **Classic Duel**   | Standard 3x3. Pure baseline.                                                                                      |
| **Shifting Board** | Every 3 rounds, the entire board rotates. Direction is `Clock::get()?.slot % 4` — deterministic from chain state. |
| **Scale Up**       | Board grows 3x3 -> 4x4 -> 5x5 as correct answers accumulate. Same win condition (3 in a row) at every size.       |

Two more are planned: [**Blitz**](/mindduel-docs/features/game-modes.md) (5-minute on-chain timer per turn) and **Ultimate TTT** (9x9 meta-grid). See the [Roadmap](/mindduel-docs/resources/roadmap.md).

### 4. On-chain hint micro-economy

Five purchasable hints, each priced 0.001-0.005 SOL. Every hint splits 80% to the platform treasury and 20% back into the active match's pot — so spending hints actually grows the prize you are competing for. Each hint type can only be bought once per player per game (enforced by a bitmask on a `HintLedger` PDA).

See [Hint Economy](/mindduel-docs/features/hint-economy.md) for the full price list.

## What is on-chain vs off-chain

| Concern                                  | Where it lives                        |
| ---------------------------------------- | ------------------------------------- |
| Player funds                             | Escrow PDA (on-chain)                 |
| Board state, turn, current commitment    | GameAccount PDA (on-chain)            |
| Hint usage tracking                      | HintLedger PDA (on-chain)             |
| Win/draw/timeout detection               | Anchor program (on-chain)             |
| Trivia question pool                     | Backend (off-chain, stateless)        |
| Match metadata for leaderboard / history | Postgres (off-chain mirror)           |
| Real-time UI sync                        | WebSocket relay (off-chain transport) |

If the backend disappears, in-progress games still settle correctly on-chain. The backend is a convenience layer — never a trust assumption.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mindduel.gitbook.io/mindduel-docs/overview/solution.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.