Agents that get paid.

What is agents.u.cash?

The agent + merchant surface for the 402 Online Protocol - a non-custodial way for AI agents, humans, and merchants to pay and be paid over plain HTTP.

A buyer requests a priced resource; the server answers HTTP 402 with a list of every way to pay (accepts[]) - one entry per accepted coin. The buyer picks one, pays the seller's own wallet the exact amount. The platform detects the payment on-chain and settles automatically (within a few minutes). To settle instantly, the buyer can optionally POST the transaction hash to /v1/verify. No cryptographic proof is needed; the chain itself is the proof. No one in the middle holds funds.

Capabilities

Everything an agent or merchant needs to charge for - and pay for - digital goods, without custody.

System architecture

Agents is the interaction layer: API, SDKs, MCP, and the 402 door. Settlement runs through pay.u.cash, and funds always move direct buyer to seller - the platform never holds them.

Quickstart

Become a seller in four calls. Base URL: https://agents.u.cash

# register (free + instant; works at $0)
curl -X POST https://agents.u.cash/v1/signup \
  -H 'Content-Type: application/json' \
  -d '{"email":"me@agent.dev","password":"longpass","agreed_to_terms":true}'
# -> {"response":{"api_key":"…","activated":false}}

# your account works immediately at $0. (Verify your email any time
# for $5 free credit, up to $2,500 in transactions; POST /v1/top-up adds more later.)

# set your receive address (where buyers pay you)
curl -X POST https://agents.u.cash/v1/wallets \
  -H 'X-Api-Key: $KEY' -d '{"asset":"btc","address":"bc1q…"}'

# create a priced resource
curl -X POST https://agents.u.cash/v1/resources \
  -H 'X-Api-Key: $KEY' -d '{"amount":0.05}'
# -> {"response":{"res_id":"res_…"}}
# share:  https://agents.u.cash/r/{res_id}

3 · Buy (a buyer pays for a resource)

# fetch the 402 door (no key needed)
curl https://agents.u.cash/r/res_… | jq '.response.accepts[0]'
# -> {"scheme":"detect","asset":"btc","payTo":"bc1q…","amount":"16230","challengeId":"chal_…"}

# pay `payTo` exactly `amount` from your wallet. The platform detects
# the on-chain payment and settles automatically (GET /r/{res_id} ->
# {"settled":true} within minutes) - nothing else required.

# To settle instantly instead, POST the on-chain tx hash (optional):
curl -X POST https://agents.u.cash/v1/verify \
  -H 'Content-Type: application/json' \
  -d '{"challengeId":"chal_…","hash":""}'
# -> {"settled":true} | {"status":"pending","confirmations":0,"required":3}

4 · UCP checkout (a buyer agent creates a cart)

# buyer-side: create a multi-item checkout session (merchant from ?cloud=)
curl -X POST https://agents.u.cash/checkout-sessions?cloud=<merchant-token> \
  -H 'Content-Type: application/json' \
  -d '{"line_items":[{"item":{"id":"res_..."},"quantity":1}],"currency":"USD"}'
# -> {"id":"cs_...","status":"incomplete","line_items":[...],"ap2":{"merchant_authorization":"..."}}

# complete -> mints the per-coin payment challenges
curl -X POST https://agents.u.cash/checkout-sessions/cs_.../complete?cloud=<merchant-token>
# the buyer pays each challenge; the session auto-completes on settlement
# GET /orders/cs_... -> per-item fulfillment status

API reference

Auth: send api_key in the X-Api-Key header (from /v1/signup). Full machine spec: OpenAPI · llms.txt.

Account

Sell - the 402 flow

Buy - public

Rate limits (per IP): signup 10/hr, others 30–60/min, /r/ 120/min. Over → 429 uxc_rate_limited. Errors: {success:false, error_code, message}.

UCP checkout - public (?cloud= or custom domain)

UCP endpoints resolve the merchant from the host or ?cloud=<token>; no X-Api-Key. Responses are RFC 9421-signed (ES256). Rate-limited per IP (checkout 60/min, catalog 120/min, orders 60/min).

For AI agents

agents.u.cash is built for autonomous agents. Drive the whole seller surface as tools, or integrate from code with zero-dependency SDKs.

// claude_desktop_config.json
{
  "mcpServers": {
    "agents-u-cash": {
      "command": "php",
      "args": ["/path/to/agents/mcp/server.php"],
      "env": { "UXC_API_KEY": "your_key" }
    }
  }
}

# Python
pip install agents-u-cash

# JavaScript
npm install @ucash/agents

from agents_u_cash import AgentsUCash
agent = AgentsUCash(api_key="…")
agent.set_wallet("btc", "bc1q…")
res = agent.create_resource(amount=0.05)
acc = agent.create_challenge(res["res_id"])

LLM-friendly docs

• llms.txt - the full API, flows, concepts, and links in one plain-text file (point an LLM here).
• OpenAPI 3.1 spec - structured, for tooling / SDK generation.
• 402.onl - the vendor-neutral protocol spec (scheme families, accepts[], security model).