Obolus

An MCP server that gives an AI agent a disposable Algorand wallet, so it can pay for x402 resources without a human provisioning anything.

The name is the coin paid to the ferryman for passage: small denomination, one purpose, spent and gone.

agent → x402_fetch(url) → 402 → sign → pay → body

x402 has over a thousand listed resources and almost no buyers — a handful of wallets account for nearly all volume, and they are scripted loops rather than agents. The rail exists; nothing can reach it. Obolus is the buyer-side piece: account setup, opt-in, signing and sweeping handled invisibly, so an agent just spends.

Install

uv tool install obolus

uv tool install rather than uvx: uvx re-resolves dependencies on every invocation, which is the wrong trade for something an agent calls constantly. pipx install obolus works too.

Add it to Claude Code

claude mcp add obolus -e OBOLUS_NETWORK=testnet -- obolus-mcp

Add it to any other MCP client

{
  "mcpServers": {
    "obolus": {
      "command": "obolus-mcp",
      "env": { "OBOLUS_NETWORK": "testnet" }
    }
  }
}

It starts on testnet. Mainnet is never disabled — Obolus is meant to make real payments — but it is never what you get by forgetting to choose.

Fund it

A new vault holds nothing, and the order is forced by the chain:

obolus vault          # says which of the three steps you are on
obolus vault qr       # scannable codes for the two things you can send

Step 3 before step 2 fails. An Algorand account cannot receive an asset it has not opted into — the transfer is rejected outright, it does not sit pending. That is why the QR codes encode the asset id and not just the address, and why wallet_funding_info tells you which step you are on every time rather than only on error.

The QR codes carry no amount. You type that into your own wallet, where you see it before confirming.

Use it

Three tools, deliberately:

There is no tool for any particular merchant. Everything is reached through x402_fetch, because the moment a wallet grows first-class verbs for one seller it stops being a wallet.

What bounds a loss

The session balance, enforced by the chain. Payments come from a short-lived session account funded from your vault, never from the vault itself. A session cannot spend what it does not hold, and that is true regardless of what any code here does.

Everything else is in-process and configurable in config.toml inside your data directory:

[caps]
session_balance_micro = 5000000   # $5 per session
per_call_micro        = 500000    # $0.50 per call
daily_micro           = 2000000   # $2 a day, resets 00:00 UTC
allowlist             = []        # payTo addresses or hostnames; empty = any

[session]
idle_timeout_seconds  = 600       # close and sweep back after this

[files]
# root = "/path/you/choose"       # off unless set - see Safety

Some refusals are not caps and have no config key: paying an address we control, a non-https resource on mainnet, an asset the wallet does not hold, and any challenge that is not a well-formed x402 v2 402.

Safety

Your seed is the only way back to your money. It lives in your data directory. Pointing OBOLUS_DATA_DIR at a new location creates a new wallet; it does not move the old one. Back the directory up.

File access is off by default. x402_fetch can send a file to a paid endpoint and write the response back, which is how you get an image signed or a document processed. Both are disabled unless you set [files] root, and confined to that directory when you do. This is deliberate: moving bytes off your machine is not something a spend cap can bound.

Approval is per tool, not per payment. Most MCP clients ask once and remember. That means the caps above are your real spending boundary, not the prompt — see DESIGN.md §7.1, which documents what was measured rather than what was assumed.

A settled payment proves settlement and nothing else — not that the resource was correct, honest, or worth its price.

Documentation

• CLAUDE.md — orientation, and the x402 facts that cost real debugging time to learn.
• DESIGN.md — architecture, the security model, and the limitations stated plainly.
• IMPLEMENTATION_PLAN.md — build order and what each phase actually proved.

Status

Working on testnet: payments settle, sessions open and sweep themselves, and an unclean exit is recovered on the next start. The first mainnet payment is the next milestone.