Verifiable randomness for AI agents: dice, coin flips, ranges, winners and shuffles, each one a VRF request on Arc with a proof anyone can replay. 0.05 USDC per draw, paid from your Circle Agent Wallet.

Setup

Wallet. Have your agent follow Circle's setup guide. It installs the Circle CLI, logs you in with an emailed code and creates an agent wallet. You accept Circle's terms yourself.

Funds. Fund the wallet with USDC and deposit some into Circle Gateway, for example on Arc:

circle gateway deposit --chain ARC --method direct --amount 1 --address <wallet>

Arc, Polygon, Avalanche, Base, Arbitrum, Optimism, Unichain and Ethereum balances all work.

Server. Add it to your client.

Claude Code:
```
claude mcp add d20dao -- npx -y @d20dao/mcp@0.1.0
```
Claude Desktop, Cursor and others (mcpServers in the client's MCP config):
```
{ "mcpServers": { "d20dao": { "command": "npx", "args": ["-y", "@d20dao/mcp@0.1.0"] } } }
```
On Windows, use "command": "cmd" with "args": ["/c", "npx", "-y", "@d20dao/mcp@0.1.0"] if the client cannot start npx directly. Pin the version, since the server runs with your Circle session.

Ask your agent to call setup_status; it names the next step until everything is ready.

Tools

Tool	Cost	Does
`draw`	0.05 USDC	`raw`, `coinFlip`, `dice` (up to 128), `range`, `chooseOne`, `chooseMany`, `shuffle` (up to 256 items). Returns the result with request, fulfillment and proof links.
`get_result`	free	Reads a draw by `paymentId` or a request by `requestId`.
`setup_status`	free	Checks the CLI, login, wallet, Gateway balance and today's spending.

An optional seed (up to 64 bytes) is bound on chain to the draw, so a raffle can name its round before the result exists. Give each separate draw its own seed: an identical draw within five minutes returns the earlier one without paying.

A draw usually answers in about ten seconds, but it can take longer. If your client's tool timeout is short (60 seconds is a common default), raise it; a retry after a timeout returns the same draw rather than paying twice.

Settings

Variable	Default
`D20_DAILY_LIMIT_USDC`	`1`	Spending cap per UTC day, shared by every server process of the user. `0` turns paid draws off.
`D20_NETWORK`	`mainnet`	`testnet` uses the Arc Testnet API and a testnet CLI login (`circle wallet login <email> --testnet`).
`D20_PAY_CHAIN`	first funded	Circle CLI chain code to pay from, such as `ARC` or `BASE`.
`D20_WALLET_ADDRESS`	first agent wallet	Agent wallet to pay from.
`D20_CIRCLE_CLI`	`circle` on PATH	Path to the CLI's `dist/index.js`.
`D20_MCP_HOME`	`~/.d20dao-mcp`	Where the spending record is kept.

Safety

The server holds no keys. The Circle CLI signs, and your Circle wallet limits apply. It never accepts Circle's terms for you: CIRCLE_ACCEPT_TERMS is kept out of the CLI it runs, and DO_NOT_TRACK is set so your item labels stay out of the CLI's telemetry.
It pays only api.d20dao.org (or api-testnet.d20dao.org) and never more than 0.05 USDC per draw. If the CLI ever reports another seller, that draw comes back with a warning and paid draws stop until you delete halt.json from the server's home folder.
Each draw reserves its price in the daily record before paying; if the record cannot be written, it does not pay.
A draw that is still pending is finished for free with get_result. If the answer is lost after payment, the server resends the payment the CLI signed, which the API honours at most once.
A result says charged: false only when that is known. When it says unknown, do not draw again; check with get_result or the wallet.
draw is marked as a tool with side effects, so clients ask before running it unless you allow it.

Verify

Every result links its request and fulfillment transactions and a proof page. Replay the proof yourself with @d20dao/vrf-sdk; see verification and the agent API guide.