Developers

Build on open money infrastructure.

Non-custodial payment rails with a universal embed, a REST API and signed webhooks, SDKs across 12 language registries, an MCP server for agent runtimes, and open standards (HTTP 402, UCP). Your keys, your funds, your code.

Quick start Browse 125 integrations awesome-ucash ↗

Quick start

Three paths: drop in the embed, call the API server-side, or verify a webhook. All you need is a publishable Store Cloud Token from pay.u.cash Account then Stores.

1. Universal embed (no server)

<!-- drop anywhere; publishable token, browser-safe -->
<script src="https://pay.u.cash/embed.js"
    data-cloud="st_your_store_token"
    data-amount="10" data-currency="USD"></script>

2. Create a checkout (server-side)

$ curl -X POST https://pay.u.cash/payment/ajax.php \
    -d function=create-transaction \
    -d amount=10 -d currency_code=USD \
    -d external_reference=order_123 \
    -d cloud=st_your_store_token -d idempotent=1
 
# 200 OK
{ "success": true, "response": [ "https://pay.u.cash/checkout/...", 12345 ] }

The first value starting with http(s):// is the payment link; the first positive integer is the transaction id. Redirect the buyer to the link. The request is idempotent per external_reference.

3. Verify a settlement webhook

# header: X-Webhook-Signature: t=<unix-seconds>,v1=<hex>
expected = HMAC_SHA256( "<t>." + raw_request_body, webhook_secret )
# timing-safe compare against v1; reject if abs(now - t) > 300s

Every official SDK ships the same createCheckout + verifyWebhook pair, so this contract is identical across languages.

SDKs and libraries

Pick your language. Each SDK is a thin, zero-dependency client over the same API. Live packages are published to their registry; build-ready packages are complete and tested, awaiting a registry credential.

JavaScript / TypeScript npm · live

npm i @ucash/ucash-cli (CLI), ucashpay-react, vue, svelte, solid, preact, angular, next, nuxt, astro, deno. npm ↗

Python PyPI · live

mcp-ucashpay, langchain-ucashpay, crewai, llamaindex, agents-u-cash. autogen, langgraph, litellm, token-gate ship via OIDC once GitHub Actions is re-enabled. PyPI ↗

Rust crates.io · build-ready

ucashpay. Zero-dep, create_checkout + verify_webhook. repo ↗

Java Maven Central · build-ready

dev.ucash:ucashpay-java. Java 11+, HttpURLConnection only. Central-publishing plugin wired. repo ↗

.NET (C#) NuGet · build-ready

UdotCASH.UcashPay. .NET 6+, xUnit-tested. repo ↗

Elixir Hex · build-ready

ucashpay. Stdlib-only, mix-tested. repo ↗

Deno / TypeScript JSR · build-ready

@ucash/pay-deno. repo ↗

Flutter / Dart pub.dev · build-ready

ucashpay. repo ↗

Ruby / Rails RubyGems · build-ready

ucashpay. Stdlib-only, tested. repo ↗

PHP Packagist · build-ready

ucash/ucashpay-laravel, ucash/ucashpay-symfony. Auto-publish from git tags. repo ↗

Swift Swift PM · live

UcashPay, consumed from the git tag. repo ↗

Go pkg.go.dev · live

github.com/UdotCASH/ucashpay-go, git-indexed, go-test-covered. repo ↗

120+ more plugins, bots, and framework integrations in the full catalog: /integrations and awesome-ucash.

AI agents and HTTP 402

Put AI agents on the HTTP-402 protocol: they sell priced resources and buy services per request, in crypto or via their own Stripe. Non-custodial, multi-rail.

Agent SDKs

agents-u-cash on npm and PyPI. Detect a 402, pay it, retry with the X-PAYMENT receipt.

MCP server

mcp-ucashpay on PyPI exposes U.CASH Pay as MCP tools for Claude Desktop, Cursor, and any MCP client. repo ↗

Cursor and Claude skills

The ucashpay-skills pack: a Cursor rule and a Claude Code skill with the integration cheat-sheet. repo ↗

APIs and webhooks

create-transaction

POST /payment/ajax.php with function=create-transaction. Idempotent per external_reference. Returns the payment link and transaction id.

test-connection

POST /api.php with function=test-connection to validate a webhook URL end to end before going live.

X-Webhook-Signature

HMAC-SHA256 over t.raw_body, a 300-second replay window, constant-time compare. Retry-safe and tamper-proof.

Per-store credentials

Each store gets its own publishable Cloud Token and Webhook Secret. Store-level, not account-wide, by design.

Custom tokens

Self-serve any ERC-20, BEP-20, TRC-20, SPL, or token on the 22 supported networks via the API.

Full reference

The complete API, webhook, and SDK reference lives on the Pay app. pay.u.cash ↗

Open standards

HTTP 402

Any URL can return 402 Payment Required with an accepts list. Agents negotiate and pay automatically. Spec at 402.onl.

UCP

The Universal Commerce Protocol: checkout sessions, orders, multi-item mixed-currency carts. Spec at ucp.dev.

Web3 names

Interoperable ENS, Unstoppable Domains, and FIO resolution for human-readable payouts, on by default.

Agent discovery

A machine-readable /.well-known/ucp profile and /catalog.json let agents find and pay for your resources autonomously.

Resources

Everything is open source

125+ plugins, SDKs, and integrations under MIT (libs) and GPLv2 (WordPress plugins). Fork it, ship it, extend it.