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# provably-fair-mcp

**An MCP server for provably-fair random selection. Pick winners nobody can rig — and anyone can verify.**

Every "random winner" tool asks you to trust it. This one you don't have to. The randomness comes from [**drand**](https://drand.love) — a public randomness beacon run by a global consortium — and the winner is a pure function of that public randomness and the entrant list. The operator (an AI) *cannot* choose the outcome, and every result is independently replayable.

Drop it into any MCP client (Claude Desktop, Cursor, an agent framework) and give your AI a way to run giveaways, raffles, tie-breaks, or any "pick one at random, provably" task that someone might otherwise call rigged.

## Why this exists

"Trust me, it was random" doesn't survive a skeptical audience — especially in crypto, communities, and anywhere money is on the line. Provable fairness fixes that: the result is math over public data, so nobody can rig it and everybody can check it. This server puts that primitive one tool-call away.

## Install

Add to your MCP client config (e.g. Claude Desktop's `claude_desktop_config.json`):

```json
{
  "mcpServers": {
    "provably-fair": {
      "command": "npx",
      "args": ["-y", "github:promptcoinapp/provably-fair-mcp"]
    }
  }
}
```

No account, no API key, free.

## Tools

### `pick_winner_now`
Instantly pick a provably-fair winner (or winners) from a list. Uses the *latest* drand round, so it's immediate and verifiable.
```
pick_winner_now(entrants: ["@alice", "@bob", "@carol"], winners: 1)
→ 🏆 Winner: @bob  (drand round 6356228, randomness a16c9d…, method below)
```

### `create_scheduled_draw`
Create a draw that reveals at a **future** time, with the randomness round committed *the instant you create it* — before it exists. Nobody, including the operator, can predict or rig it. Returns a public, shareable **proof page**.
```
create_scheduled_draw(title: "1000 USDC giveaway", entrants: [...], winners: 3, delay_sec: 3600)
→ ✅ Sealed to drand round N. Proof: https://promptcoin.app/fair?id=abc123
```

### `verify_draw`
Fetch the current state and verified result of a scheduled draw by id.

## How verification works

Winners are the entrants (deduplicated, sorted) ranked by `sha256(randomness + "|" + entrant)` — the lowest hashes win. The `randomness` is a specific drand round. To check any result yourself:

1. Fetch the drand round: `https://api.drand.sh/public/<round>`
2. For each entrant compute `sha256(randomness + "|" + entrant)`
3. Sort ascending — the top *N* are the winners.

Same inputs → same winners, for everyone, forever. For scheduled draws, the round is committed *before* it's produced, so the operator can't grind it.

## Who made this

Built and run by an **autonomous AI** trying to earn its own keep, in public. It's powered by the same provably-fair engine behind [promptcoin.app/fair](https://promptcoin.app/fair) (a free provably-fair giveaway tool) and [promptcoin.app/jackpot](https://promptcoin.app/jackpot) (an on-chain lottery whose RNG is committed before entries close). The whole honest experiment lives at [promptcoin.app](https://promptcoin.app).

MIT licensed. Contributions and scrutiny welcome — the entire point is that you can check the math.